Anatomy Past Papers PDF

Index 1.Developmental Timeline and Gametogenesis - Page 1 3.Germ Cell Derivatives, Placenta, Fertilization - Page 18 2.Developmental Period 1, 2, 3 & 4 - Page 59 4.Previous Year Questions (general embryology) - Page 87 Epithelial Tissue and Glands - Page 107 Connective Tissue - Page 130 General Histology - Page 143 Previous Year Questions Histology - Page 162 Arthology, Osteology and Joints - Page 178 Cerebrum & Nervous System Development - Page 195 Cerebellum; Ventricles and Brainstem - Page 226 Meninges; Limbic System; Basal Ganglia; White Matter - Page 255 Spinal Cord & Autonomic Nervous System - Page 274 CNS Blood Supply and Lesions of Brainstem - Page 290 Previous Year Questions (Neuro Anatomy) - Page 316 Scalp; Head and Neck; Vascular Supply - Page 362 Parotid Gland & Triangles of Neck - Page 374 Cranium; Cranial Cavity - Page 399 Cranial Nerves and Cranial Nerve Lesions - Page 420 Pharyngeal Arch - Page 436 Trachea; Pharynx and Larynx - Page 445 Eyes ; Ear and Nose - Page 463 Previous Year Questions (Head and Neck) - Page 484 Spinal Cord and Vertebra - Page 534 Previous Year Questions (Back Region) - Page 552 Embryology of CVS & AP Septum & Embryonic Veins - Page 558 Surface Landmarks - Page 586 Thorax - Vascular Supply - Page 609 Bronchopulmonary Segments & Thoracic Wall - Page 634 Previous Year Questions (Thorax) - Page 662 Brachial Plexus; Upper Arm Nerve Supply - Page 692 Bones of the Hand; Carpal and Metacarpals - Page 712 Scapula and its Movements; Upper Arm Muscles and Bones - Page 721 Cubital Fossa; Arm and Forearm Muscles - Page 757 Upper Extremity Arterial Supply, Venous and Lymphatic Drainage - Page 776 Upper Limb Nerve Lesions - Page 789 Index Previous Year Questions (upper limb) - Page 800 Diaphragm & Umbilical Cord - Page 848 Neurovascular Bundle and Mesentry - Page 865 Liver and Gallbladder - Page 878 Abdominal Wall & Embryology of Abdomen - Page 891 Inguinal Region & Abdominal Cavity - Page 914 Vascular Supply of Abdomen & Stomach - Page 931 Intestine & Colon - Page 954 Spleen; Pancreas; Kidney & Ureter - Page 967 Previous Year Questions (abdomen) - Page 984 Genitourinary System Embryology & Neurovascular Supply - Page 1018 Male Reproductive Tract - Page 1068 Female Reproductive Tract - Page 1088 Anal Canal & Rectum - Page 1110 Previous Year Questions(Pelvis and Perineum) - Page 1118 Lower Extremity Nerve Supply - Page 1129 Lower Extremity Muscles - Page 1144 Ligaments; Joints and Bones of Lower Limb - Page 1168 Vascular Supply and Canals - Page 1188 Previous Year Questions (Lower Limb) - Page 1204 Developmental Timeline and Gametogenesis 1. In a couple undergoing in-vitro fertilization for 4 years, which resulted in the birth of a female child today, if a sample is drawn for investigation, at which stage of meiosis would the oocyte be? (or) In which of the following meiotic stages can the oocyte wound be found in a newborn baby? A. Prophase I B. Metaphase I C. Anaphase I D. Telophase I ---------------------------------------- 2. When does a secondary oocyte complete its second meiotic division to become a mature ovum? A. At ovulation B. Before ovulation C. At fertilization D. At puberty ---------------------------------------- 3. Which of the following events occurs immediately following the completion of meiosis II? A. Degeneration of the zona pellucida B. Sperm penetration of the corona radiata C. Formation of a female pronucleus D. Appearance of the blastocyst ---------------------------------------- 4. Which of the following is the correct sequence of events in spermatogenesis? Spermatid Spermatocyte Spermatogonium Spermatozoa A. 3, 2, 1, 4 B. 2, 3, 1, 4 C. 3, 2, 4, 1 D. 4, 3, 2, 1 ---------------------------------------- 5. In which of the followingphase of spermatogenesis does reduction in the chromosomal number to half the original number occur? A. During mitosis B. Meiosis - I C. Meiosis - II D. None of above ---------------------------------------- 1 6. Which of the following statements is true about spermatogenesis? A. Occurs in the spermatic cord B. Spermatogonium forms sperm in 74 days C. Meiosis occurs only after secondary spermatocyte is formed D. Spermatid is formed from spermatozoa ---------------------------------------- 7. At which phase of the menstrual cycle is the first polar body extruded? A. Menstruation B. Ovulation C. Fertilization D. Menarche ---------------------------------------- 8. Primordial germ cells are themselves developed from which of the following embryological structures? A. Epiblast B. Neural crest C. Coelomic epithelium D. Genital ridge ---------------------------------------- 9. Which of the following statements is true regarding reductional division? A. Meiosis is needed to produce large number of eggs and sperms. B. Germ cell undergoes division to form haploid cell and increase their numbers. C. Occurs in germ cell, which results in diploid cells. D. One spermatocyte produces one sperm, and one oocyte produces one ovum. ---------------------------------------- 10. At which level of spematognesis does the independent assortment of chromosomes occur? A. Primordial germ cells to spermatogonia B. Spermatogonia to primary spermatocyte C. Primary spermatocyte to secondary spermatocyte D. Secondary spermatocyte to spermatids ---------------------------------------- 11. What is the expected fertilization window after ovulation for a 28-year-old woman with a regular 28-day menstrual cycle if her last period was between February 23rd and 28th, 2024, and she's aiming to conceive? A. 24 hours B. 12 hours Page 2 2 C. 36 hours D. 48 hours ---------------------------------------- 12. The Conceptus reaches the uterine cavity at which stage and on which day? A. 1 cell, Day 2 B. 2 cells, Day 4 C. 16 cells, Day 5 D. 32 cells, Day 4 ---------------------------------------- 13. At which stage is the oocyte retrieved during in-vitro fertilization treatment after a couple decides to undergo the procedure? A. Oogonia B. Primary oocyte C. Secondary oocyte D. Primordial germ cell ---------------------------------------- 14. Which of the following is responsible for the arrest of the primary oocyte in the diplotene stage of prophase-1? A. Oocyte maturation inhibitor B. Oocyte maturation stimulator C. Acetylcholine D. Oestrogen ---------------------------------------- 15. Regarding prophase of meiosis-I, which of the following is a true statement? A. Chromosomes separate B. Resultant cell is diploid C. Resultant cell is haploid D. Sister chromatids replicate ---------------------------------------- 16. In which phase of meiosis do Leptotene and Pachytene occur? A. Anaphase II B. Telophase II C. Prophase I D. Metaphase I ---------------------------------------- 17. Which of the chromosome responsible for determining the sex of the resulting fetus? Page 3 3 A. Metric B. Acrocentric C. Submetacentric D. None ---------------------------------------- Correct Answers Question Correct Answer Question 1 1 Question 2 3 Question 3 3 Question 4 1 Question 5 2 Question 6 2 Question 7 2 Question 8 1 Question 9 2 Question 10 3 Question 11 1 Question 12 4 Question 13 3 Question 14 1 Question 15 2 Question 16 3 Question 17 2 Solution for Question 1: Option A: Prophase I At the time of birth, the oocyte is dormant in the diplotene stage (resting stage during prophase I) in all females, regardless of the type of conception- natural/ IVF. Stages of prophase- I Leptotene Zygotene Pachytene Diplotene Diakinesis Leptotene Zygotene Pachytene Diplotene Diakinesis Page 4 4 Leptotene Zygotene Pachytene Diplotene Diakinesis Option B: Metaphase I In metaphase I, the homologous pairs of chromosomes align on each side of the equatorial plate. The secondary oocyte is arrested in the metaphase-2 stage of meiosis II, which is completed when fertilization occurs. Option C: Anaphase I Anaphase I is the 3rd stage of meiosis I & follows prophase I & metaphase I. Sister chromatids of every chromosome separate & start to move towards the opposite pole of the cell. The separation and the movement are because of the shortening of the kinetochore microtubules. Option D: Telophase I Telophase I is the last stage of meiosis I followed by meiosis II. Four daughter cells are formed Nuclear membranes form around each set of chromosomes & decondensation of the chromosomes occurs. Cytokinesis splits the sets of chromosomes into new cells, two haploid cells. Solution for Question 2: Option C: At fertilization The primary oocyte is arrested in the diplotene stage of Meiosis I. Only after the luteinizing hormone surge, it will form a secondary oocyte. The secondary oocyte is arrested in metaphase II of meiosis II The secondary oocyte completes its second meiotic division to become a mature ovum at fertilization. Option A: At ovulation A secondary oocyte begins meiosis II at ovulation, but this division is arrested at metaphase. The secondary oocyte will remain arrested in metaphase until a sperm penetrates it at fertilization. If fertilization does not occur, the secondary oocyte degenerates. Option B: Before ovulation Meiosis I is a reductional division during which the maternal & paternal chromosomes are separated. Please note that before ovulation, due to the LH surge, the primary oocyte completes meiosis I and releases the secondary oocyte and first polar body. Page 5 5 A Luteinizing hormone surge occurs 36 hours before ovulation, and a luteinizing hormone peak occurs 12 hours before ovulation (1 polar body released). Option D: At puberty The oocyte is resting in the diplotene stage of prophase 1 (meiosis I) at the time of birth. Meiosis I completed at the time of ovulation (puberty). A secondary oocyte & 1 polar body are released (at the time of ovulation). T he secondary oocyte is arrested in "Metaphase II" (meiosis II) till fertilization. After fertilization, 2nd polar body & ovum are released. Oocytes are protected by granulosa cells, and those not protected undergo atresia. Solution for Question 3: Option C: Formation of a female pronucleus The secondary oocytes stop in the metaphase of meiosis II and remain in this meiotic stage until fertilization. After fertilization, the secondary egg cell completes meiosis II and forms a mature ovum and a polar body. The nucleus of the mature egg cell is called the female pronucleus, which fuses with the male pronucleus to form a zygote. Incorrect otpions Option A: Degeneration of the zona pellucida Oocytes are protected by granulosa cells, and those not protected undergo atresia. Degeneration of the zona pellucida happens on day 5 after fertilization Option B: Sperm penetration of the corona radiata After ejaculation, Sperms reach the posterior fornix of the vagina, and it takes 2 minutes to reach the ampulla of the fallopian tube. Acrosome breaks down and releases acrosin to fertilize oocyte (to disperse the corona radiata of zona pellucida of oocyte). Acrosin (Hyaluronidase) will soften the zona pellucida (Acrosome reaction). Sperm penetration of the corona radiata is a process leading to fertilization Option D: Appearance of the blastocyst Advanced morula enters the uterine cavity on Day 4 and changes to "Blastocyst." It contains Blast cells & cyst-like cavities. Contains: Outer cell mass-Trophoblast [helps in placental formation] and inner cell mass – Embryoblast The appearance of the blastocyst occurs on day 4 after fertilization Advanced morula enters the uterine cavity on Day 4 and changes to "Blastocyst." It contains Blast cells & cyst-like cavities. Contains: Outer cell mass-Trophoblast [helps in placental formation] and inner cell mass – Embryoblast Page 6 6 Solution for Question 4: Option A: 3, 2, 1, 4 Spermatogenesis is a process in which haploid spermatogonium undergoes mitotic division to form primary spermatocytes. The sequence starts from primordial germ cell - spermatogonium - primary spermatocyte - secondary spermatocyte - spermatid - spermatozoa (sperm). Solution for Question 5: Option B: Meiosis - I Meiosis is a process where a single cell divides twice to produce four cells containing half the original amount of genetic information. The first meiotic division is the reduction division, and each primary spermatocyte yields two secondary spermatocytes. Each secondary spermatocyte contains 23 (Haploid) chromosomes consisting of two varieties, 22+X and 22+Y. Here 22 are autosomes, and X & Y are sex chromosomes. Option A: During mitosis Mitosis is a process in which the cell undergoes division to produce offspring. In mitosis, daughter cells have the same chromosomes as the parent (diploid). During the initial phase of spermatogenesis, the spermatogonia undergoes continuous mitosis division until the formation of the primary spermatocyte. Option C: Meiosis - II Page 7 7 During spermatogenesis, the PGCs (Primordial germ cells or spermatogonia) undergo several mitotic divisions to form primary spermatocytes. Primary spermatocyte after meiosis I → two secondary spermatocytes (with 4 haploid chromosomes) → Meiosis II→ four haploid daughter cells. Solution for Question 6: Option B. Spermatogonium forms sperm in 74 days Spermatogenesis is a process in which spermatogonium undergoes mitotic division to form primary spermatocytes. Primary spermatocytes undergo meiosis I into two secondary spermatocytes. Each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II. Spermatids are transformed into spermatozoa(sperm) by the process of spermiogenesis. The duration of spermatogenesis, which is the formation of sperm from spermatogonia, is 74 days. Starting from primordial germ cell (2n) → spermatogonium(2n) → primary spermatocyte (2n)→ secondary spermatocyte(n) → spermatid(n) → spermatozoa(n) (sperm). Incorrect options Option A: Occurs in the spermatic cord Seminiferous tubules are the primary site of spermatogenesis. The spermatic cord is a paired structure whose main function is to suspend the testes in the scrotum. Option C: Meiosis occurs only after a secondary spermatocyte is formed Spermatogonium undergoes mitotic division to form primary spermatocytes. Primary spermatocytes undergo meiosis I and forms two secondary spermatocytes. Each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II. Option D. Spermatid is formed from spermatozoa Spermatozoa are formed from spermatids by a process of spermiogenesis. Solution for Question 7: Option B: Ovulation The oocyte is resting in prophase I (1st meiotic division) at the time of birth. Primary oocyte completes it's meiosis I at the time of ovulation (puberty) and releases secondary oocyte & 1st polar body. The secondary oocyte is arrested in metaphase II (meiosis II) till fertilization. After fertilization, 2nd polar body & ovum are released. Oocytes are protected by granulosa cells and those are not protected undergo atresia. Page 8 8 Option A: Menstruation At ovulation, the secondary oocyte begins meiosis II, but this division is arrested at metaphase. The secondary oocyte & 1st polar body are released (at the time of ovulation). Option C: Fertilization The primary oocyte is arrested in the diplotene stage of meiosis I. Only after luteinizing hormone surge it will form a secondary oocyte. The secondary oocyte & 1st polar body are released (at the time of ovulation). The secondary oocyte completes its second meiotic division to become a mature ovum at fertilization. Option D: Menarche Meiosis I completed at the time of ovulation (puberty). The secondary oocyte & 1st polar body are released (at the time of ovulation). Menarche is the first menstrual cycle until then arrested in the diplotene stage of meiosis I. Solution for Question 8: Option A: Epiblast Primordial germ cells are germ cells that are derived from the epiblast at the end of 2nd week. These primordial germ cells migrate to an endodermal layer of the yolk sac in the 4th week and further towards the genital ridge by the 5th week. Aberrant migration of these primordial germ cells leads to teratomas: sacrococcygeal teratoma & oropharyngeal teratoma. Page 9 9 Option B: Neural crest Neural crest derivatives are the peripheral nervous system (including ganglia). Option C: Coelomic epithelium The coelomic epithelium develops into the peritoneum, pleura & the surface of the ovary. Option D: Genital ridge. The gonadal/genital ridge has mostly mesenchyme and cells of underlying mesonephric origin. Mainly from the intermediate mesoderm. Solution for Question 9: Option B: Germ cell undergoes division to form haploid cell and increase their numbers. Meiosis is a process where a single cell divides twice to produce four cells containing half the original amount of genetic information. The first meiotic division is known as the reduction division, and each primary spermatocyte yields two secondary spermatocytes, each of which contains 23 (Haploid)chromosomes consisting of two varieties, 22+Xand 22+Y. Here, 22 are autosomes, and X & Y are sex chromosomes. Meiosis requires 2 divisions – meiosis I & meiosis II to reduce the number of chromosomes to a haploid number of 23. Page 10 10 Incorrect options Option A: Meiosis is needed to produce a large number of eggs and sperm. Meiosis is cell division that takes place in the germ cells to generate male & female gametes, sperm & egg cell, respectively. Meiosis is needed to produce haploid cells so that the equilibrium of the system is not disturbed and the female egg and male sperm contain the diploid number of chromosomes. Option C: Occurs in germ cells which results in diploid cells. The first meiotic division is known as the reduction division, and each primary spermatocyte yields two secondary spermatocytes. In meiosis, homologous chromosomes align themselves in pairs, a process called synapsis. Homologous pairs then separate into two daughter cells, reducing chromosome number from diploid to haploid. Page 11 11 Option D: One spermatocyte produces one sperm, and one oocyte produces one ovum. At the end of meiosis II, gametes are formed in which each contains 23 chromosomes. One spermatocyte produces 4 sperms (1:4) & one oocyte produces one ovum (1:1). Solution for Question 10: Option C: Primary spermatocyte to secondary spermatocyte Independent assortment: The separation of maternal & paternal chromosomes in a random manner is called an independent assortment. It occurs in meiosis-1, a reductional division. It occurs when the primary spermatocyte becomes a secondary spermatocyte. Each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II. Spermatids are transformed into spermatozoa(sperm) by the process of spermiogenesis. It occurs in meiosis-1, a reductional division. It occurs when the primary spermatocyte becomes a secondary spermatocyte. Each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II. Spermatids are transformed into spermatozoa(sperm) by the process of spermiogenesis. It occurs in meiosis-1, a reductional division. It occurs when the primary spermatocyte becomes a secondary spermatocyte. Each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II. Spermatids are transformed into spermatozoa(sperm) by the process of spermiogenesis. Option A: Primordial germ cells to spermatogonia During spermatogenesis, the primordial germ cells undergo several mitotic divisions to form primary spermatocytes. Primary spermatocyte undergoes first meiotic division to form a secondary spermatocyte, which further undergoes second meiotic division to produce four equal haploid cells. Option B: Spermatogonia to primary spermatocyte Spermatogonia to primary spermatocyte is a “mitotic” division. Spermatogenesis is a process in which diploid spermatogonium undergoes mitotic division to form primary spermatocytes. Option D: Secondary spermatocyte to spermatids Secondary spermatocyte to spermatids takes 74 days, and approximately 300 million sperm cells are produced Solution for Question 11: Option A: 24 hours The luteinizing hormone surge occurs 36 hours before ovulation & luteinizing hormone peak occurs 12 hours before ovulation (1st Polar body released). Page 12 12 Fertilization should occur within 24 hours of ovulation; otherwise, degeneration occurs if fertilization does not occur, resulting in menstruation. The window period for fertilization for females is 24 hours, and for males is 48 hours. This mature oocyte (ovum) remains viable for fertilization for ~ 24 hours. Incorrect options Option B, C, D: Fertilization should occur within 24 hours of ovulation; otherwise, degeneration occurs if fertilization does not occur, resulting in menstruation. The window period for fertilization for females is 24 Hours, and for males is 48 Hours. This mature oocyte (ovum) remains viable for fertilization for ~ 24 hours. Solution for Question 12: Option D: 32 cells, Day 4 Conceptus enters the uterine cavity on the 4th day in the “Advanced morula” at 32 cell stage. Morula (multicellular stage) is a solid mass of blastomeres resulting from several cleavages of a zygote formed after 3rd day of fertilization. Note: In in-vitro fertilization. The transvaginal insertion into the uterus is done at the 8-cell stage Option A: 1 cell, Day 2 Day 1 post-fertilization, the single cell is known as a zygote. Fertilization occurs in the ampulla of the fallopian tube. The secondary oocyte undergoes ovulation. Ovum is fertilized by sperm and forms a single-celled zygote. This zygote undergoes several cleavages to form a morula on day 3, which is a 16-cell stage. The multicellular stage is called morula → 12,16,32 & >32 cell stage (Morula is 16-cell stage). Hence, the 1-cell stage is not a morula. Option B: 2 cells, Day 4 Day 2 is a 2-cell stage in the fallopian tube. The zygote undergoes mitotic divisions that increase the number of cells in the zygote. Each cycle of division takes about 24 hours. Option C: 16 cells, Day 5 Day 3 is a multicellular stage with 12,16,32 &>32 cell stage (Morula is 16 cell stage). Morula moves towards entering the uterine cavity. Advanced morula (32-cell stage) enters the uterine cavity on day 4, not day 5. On day 5, implantation begins, and the blastocyst is implanted on day 6. Solution for Question 13: Page 13 13 Option C: Secondary oocyte The secondary oocyte is retrieved from the female in the in-vitro fertilization process The Graafian follicle is aspirated just before ovulation to retrieve the secondary oocyte. Option A: Oogonia. At the stage of oogonia, germ cells have not undergone meiosis to become secondary oocytes. Option B: Primary oocyte At the primary oocyte stage, germ cells have not undergone meiosis to become secondary oocytes. Option D: Primordial germ cells At the primary oocyte stage, germ cells have not undergone meiosis to become secondary oocytes. Solution for Question 14: Option A: Oocyte maturation inhibitor Oocyte maturation inhibitor acts by increasing cAMP, which leads to the arrest of the oocyte in the diplotene stage of prophase- I. LH surge at puberty reduces cAMP, removing the oocyte from its arrested state. Option B: Oocyte maturation stimulator LH surge at puberty reduces cAMP, removing the oocyte from its arrested state. Option C: Acetylcholine It is the main neurotransmitter of the parasympathetic nervous system responsible for cholinergic actions. Acetylcholine has no role in oogenesis. Option D: Oestrogen Any circulating estrogen comes from Theca interna cells Local estrogen comes from Granulosa cells On the 14th day, the ovum with surrounding Cumulus oophorus extruded from follicle collected by the fallopian tube fimbriae. Oestrogen stimulates the development and maturation of ovarian follicles and also regulate FSH release. Solution for Question 15: Option B: Resultant cell is diploid Prophase-I of meiosis I: Is a long and complex phase that is different considerably from mitotic prophase and is customarily divided into four sub-stages: Leptotene: Chromosome condensations Page 14 14 occur. Zygotene: Homologous chromosomes appear as bivalent; sister chromatids are not yet evident. Pachytene: Chromosome appears as tetrad; sister chromatids are evident; chiasma (cross over) (exchange of genetic material). Diplotene: Maternal and paternal chromosome separation There is no change in ploidy status, which means the diploid cell remains diploid. Diakinesis: It is the last stage of prophase I of Meiosis I. It is the prometaphase of the first meiotic division. Leptotene: Chromosome condensations occur. Zygotene: Homologous chromosomes appear as bivalent; sister chromatids are not yet evident. Pachytene: Chromosome appears as tetrad; sister chromatids are evident; chiasma (cross over) (exchange of genetic material). Diplotene: Maternal and paternal chromosome separation There is no change in ploidy status, which means the diploid cell remains diploid. Diakinesis: It is the last stage of prophase I of Meiosis I. It is the prometaphase of the first meiotic division. Leptotene: Chromosome condensations occur. Zygotene: Homologous chromosomes appear as bivalent; sister chromatids are not yet evident. Pachytene: Chromosome appears as tetrad; sister chromatids are evident; chiasma (cross over) (exchange of genetic material). Diplotene: Maternal and paternal chromosome separation There is no change in ploidy status, which means the diploid cell remains diploid. Diakinesis: It is the last stage of prophase I of Meiosis I. It is the prometaphase of the first meiotic division. Option A: Chromosomes separate In anaphase I chromosome separates. The chromosomes, still Bivalents, become even shorter and thicker. They gradually attach to the spindle & become aligned at a metaphase plate. Option C: Resultant cell is haploid The resultant cell is diploid. Cells become haploid after the anaphase (not prophase). Option D: Sister chromatids replicate Sister chromatids replicate in meiosis II. Solution for Question 16: Correct option : Option C: Prophase I Phases of Prophase 1 are Zygotene: Homologous chromosomes pair up to form bivalents, but sister chromatids remain distinct. Pachytene: Chromosomes appear as tetrads, with homologous chromosomes fully synapse, and sister chromatids still discernible. Crossing over, or the exchange of genetic material occurs at chiasmata. Page 15 15 Diplotene: Maternal and paternal chromosomes begin to separate, but chiasmata remain visible Diakinesis: It is the last stage of prophase I of Meiosis I. It is the prometaphase of the first meiotic division. Incorrect options : Option A: Anaphase II Sister chromatids of every chromosome separate and start to move towards the opposite pole of the cell. The separation and the movement are because of the shortening of the kinetochore microtubules. Option B: Telophase II Nuclear membranes form around each set of chromosomes and decondensation of the chromosomes occurs. Cytokinesis splits the sets of chromosomes into new cells, four haploid cells. It is the Final step of meiosis Option D: Metaphase I Alignment of paired chromosomes in the center Solution for Question 17: Option B: Acrocentric The centromere is present near the end of chromosomes. It forms a very short p arm & a very long q arm Cytogenetically, the Y chromosome is composed of two pseudoautosomal regions, a short arm and the long arm separated by a centromere, and is an acrocentric chromosome. The pseudoautosomal regions are euchromatic along with the long arm's proximal portion juxtaposed to the centromere, and a large portion of the long arm is heterochromatic. In humans, chromosome numbers 13, 14, 15, 21, 22, and Y are acrocentric. Option A: Metacentric The centromere is present in the middle part of the chromosome and is divided into two equal arms. The p & q arms are almost equal in length The shape of the metacentric chromosome is X because of the equal length of the p and q arms. In humans, chromosome numbers 1, 3, 16, 19 & 20 are examples of metacentric chromosomes. Sometimes fusion of two acrocentric chromosomes by translocation leads to the formation of one metacentric chromosome. Option C: Sub-metacentric The centromere is present near the middle part and divides the chromosome into two unequal arms. The shape of the submetacentric chromosome is L-shape. Page 16 16 In humans, Most of the chromosomes are sub-metacentric Chromosome numbers 2, 4 to 12, 17, 18, & X chromosome. Page 17 17 Germ Cell Derivatives, Placenta, Fertilization 1. Which cell, formed during oogenesis, can remain dormant for 12-40 years during a woman's reproductive lifespan? A. Primordial germ cell B. Primary oocyte C. Secondary oocyte D. First polar body ---------------------------------------- 2. The excretory system of the kidney is derived from the? A. Ureteric bud B. Metanephrons C. Mesonephrons D. None ---------------------------------------- 3. Which statement about somites, formed from the mesoderm during the 3rd week of development, is/are not true? 4th week is called the somite period Dorso-lateral part forms the sclerotome 44 pairs are present by the end of 1st month Post otic part of each paraxial mesoderm is subdivided into several cubical blocks known as somites A. 2 only B. 2 & 3 only C. 2, 3 & 4 only D. None of the above ---------------------------------------- 4. Which part of the mesoderm develops into the ribs? A. Endothoracic fascia B. Paraxial mesenchyme C. Lateral plate mesoderm D. Superficial intercostal fascia ---------------------------------------- 5. Which of the following layers form the buccopharyngeal membrane? A. Ectoderm + Mesoderm B. Ectoderm + Endoderm C. Mesoderm + Endoderm D. Ectoderm + Mesoderm + Endoderm ---------------------------------------- 6. Which of the following parts of the urogenital system is derived from the intermediate mesoderm? 18 A. Urethra B. Kidneys C. Peritoneal cavity D. Somites ---------------------------------------- 7. A newborn presents with bilious emesis, abdominal distension, and failure to pass meconium in 48 hours. The disease is associated with the failure of migration of a germ layer derivative. The nerves of the pharyngeal cleft are derived from? (or) The nerves of the pharyngeal cleft are derived from? A. Neural crest cells B. Mesoderm C. Neural plate ectoderm D. Notochord ---------------------------------------- 8. A 40-year-old woman, one month postpartum, presents with lactation failure, fatigue, amenorrhea, and loss of pubic hair. Diagnosed with gland dysfunction syndrome, the gynecologist identifies derivatives of the germ layer from which the affected gland develops. Which structure listed below is not a derivative of the same germ layer? (or) Which of the following is not a derivative of the germ layer responsible for Sheehan 's syndrome? A. Epidermis B. Parotid gland C. Neurohypophysis D. Arrector Pilorum ---------------------------------------- 9. A child presents with defects in skull bones, wide-set eyes, a murmur, poor muscle tone, respiratory difficulties, frequent infections, and feeding issues. Suspecting DiGeorge syndrome, which of the following is not associated with this condition? (or) Which of the following is not a feature of the DiGeorge syndrome? A. Skull defects B. CNS defects C. Pharyngeal arch bone defects D. Cardiac defects ---------------------------------------- 10. A 5-year-old boy with nystagmus, golden hair, and blue eyes, unable to see in sunlight due to a lack of melanin. Diagnosed with a genetic disease related to melanin deficiency, which structure listed Page 2 19 below is not derived from the same germ layer cells responsible for melanin production? (or) What is not derived from neural crest cells? A. Pharyngeal arch bones B. The dermis of the head and neck C. Pharyngeal arch muscles D. Odontoblasts ---------------------------------------- 11. All of the following muscles are derivatives of somites except? (or) All of the following muscles are derivatives of somites except? A. Masseter B. Diaphragm C. Biceps femoris D. Detrusor ---------------------------------------- 12. Which of the following muscles arises from visceral splanchnic lateral plate mesoderm? A. Myoepitheliocytes of skin glands B. Iris muscles C. Smooth muscles of the gut tube D. Detrusor ---------------------------------------- 13. Marked structure develops from which germinal layer? (or) In a 10-year-old boy with eye abnormalities, tall stature, and long slender hands, a marked structure in the photograph is observed displaced upward and outward. From which germinal layer does this structure develop? A. Endoderm Page 3 20 B. Mesoderm C. Surface ectoderm D. Neuroectoderm ---------------------------------------- 14. In a term newborn with poor feeding and lethargy, born to a 35-year-old with multiple congenital defects related to dysgenesis of neural crest cells, which type of cells is likely to be spared? A. Melanocytes B. Motor neurons C. Parafollicular cells D. Spinal ganglion cells ---------------------------------------- 15. A young woman enters puberty with around 40,000 primary ovum cells in her ovary. How many of these primary ova are ovulated during her reproductive life? A. 40,000 B. 35,000 C. 480 D. 48 ---------------------------------------- 16. What is the process known as, where genetic recombinations in meiosis result in the exchange of large DNA segments, leading to characteristics of an offspring differing from its parents? A. Crossing over B. Non-disjunction C. Alignment D. Synapsis ---------------------------------------- 17. In which stage is the secondary oocyte arrested right before ovulation? A. Prophase of meiosis I B. Prophase of meiosis II C. Metaphase of meiosis I D. Metaphase of meiosis II ---------------------------------------- 18. The extra-embryonic mesoderm is derived from which of the following structure? A. Primary yolk sac B. Secondary yolk sac C. Epiblast D. Hypoblast Page 4 21 ---------------------------------------- 19. The amnion and extra coelomic cavities are connected by the connecting stalk, which is the precursor of? A. Primary umblical cord B. Secondary umbliical cord C. Decidua parietalis D. Decidua capsularis ---------------------------------------- 20. The chorionic villi start developing by which of the following days? A. Day 28 B. Day 25 C. Day 17 D. Day 15 ---------------------------------------- 21. Which of the following make up the tertiary chorionic villi? A. The central core of cytotrophoblast covered with syncytiotrophoblast B. The central core of the extraembryonic mesoderm is covered by central cytotrophoblasts and peripheral syncytiotrophoblast C. Central maternal blood vessels surrounded by mesoderm and trophoblast D. Central fetal blood vessels surrounded by mesoderm and trophoblast ---------------------------------------- 22. During the second week of embryonic development, the bilaminar disc forms epiblast and hypoblast layers. The hypoblast cells give rise to a sac that matures further. Which type of cells line the secondary stage of this sac? A. Flattened endodermal cells B. Cuboidal endodermal cells C. Extra-embryonic mesoderm D. None of the above ---------------------------------------- 23. During a routine visit, a 14-year-old girl with recurrent upper respiratory tract infections is examined. A painless 1cm x 1cm swelling is found anterior to the left sternocleidomastoid muscle, not moving with swallowing and without drainage. What statement is true regarding this structure? (or) Which characteristic is true about the branchial cyst? A. It causes dysphagia and hoarseness B. It should always be operated C. It mostly arises from the 2nd pharyngeal arch Page 5 22 D. It moves with deglutition ---------------------------------------- 24. The Müllerian duct becomes which of the following structure in males? A. Trigone of bladder B. Prostatic utricle C. Paroophoron D. Gartner's duct ---------------------------------------- 25. Sertoli cells are derived from which of the following? (or) Sertoli cells are derived from which of the following? A. Genital swelling B. Epithelial sex cords C. Genital tubercle D. Primordial germ cells ---------------------------------------- 26. Which embryological structure gives rise to the commissure connecting the two cerebral hemispheres, facilitating the flow of non-olfactory information from the prosencephalon during brain development? A. Lamina terminalis B. Basal plate C. Alar plate D. B and C ---------------------------------------- 27. In a healthy 16-year-old girl with absent menstrual periods, normal breast development, coarse pubic and axillary hair, and a blind vaginal pouch on pelvic examination, ultrasonography reveals normal ovaries and an atretic uterus. What is the most likely underlying cause of her symptoms? (or) What is the most likely underlying cause of the symptoms in a 16-year-old girl presenting with absent menses, blind vaginal pouch, coarse pubic hair, normal breasts, and normal ovaries with an atretic uterus? A. Failure of the Mullerian duct to recanalize B. Agenesis of the paramesonephric duct C. Deficiency of 5-alpha-reductase D. End-organ insensitivity to androgens ---------------------------------------- 28. Ureter, renal pelvis, major calyx, minor calyx, and the collecting duct are derivatives of a single embryonic structure. That embryonic structure is a derivative of which of the following ? Page 6 23 (or) The ureter, renal pelvis, major calyx, minor calyx, and collecting duct are derivatives of a single embryonic structure which arises from? A. Mullerian duct B. Mesonephric duct C. Paramesonephric duct D. Mesonephric tubule ---------------------------------------- 29. Which of the following statements is true about vertebral development? A. The notochord forms the annulus fibrosis B. The sclerotome forms the nucleus pulposus C. The sclerotome surrounds the notochord only D. The sclerotome surrounds the notochord and the neural tube ---------------------------------------- 30. The rectum is derived from which structure? A. Hind gut B. Cloaca C. Urogenital sinus D. Allantoic remnants ---------------------------------------- 31. Among the following bones, which one is the skeletal derivative of the 2nd pharyngeal arch? A. Malleus B. Maxilla C. Incus D. Stapes ---------------------------------------- 32. When do testes reach the deep inguinal ring? A. 5 months B. 7 months C. 9 months D. 4 months ---------------------------------------- 33. Which among the following is a remnant of notochord? A. Nucleus pulposus B. Annulus fibrosus C. Intertransverse ligament Page 7 24 D. Ligamentum flavum ---------------------------------------- 34. Glomus type-I cells are derived from which structure? A. Surface ectoderm B. Neuroectoderm C. Endoderm D. Mesoderm ---------------------------------------- 35. What is the underlying cause of the transposition of the great vessels? A. Separation of tricuspid valve tissue from the myocardium B. Fusion of endocardial cushion C. Alignment of the infundibular septum D. Spiraling of the aorticopulmonary septum ---------------------------------------- Correct Answers Question Correct Answer Question 1 2 Question 2 2 Question 3 1 Question 4 2 Question 5 2 Question 6 2 Question 7 1 Question 8 4 Question 9 2 Question 10 3 Question 11 4 Question 12 3 Question 13 3 Question 14 2 Question 15 3 Question 16 1 Question 17 4 Question 18 1 Page 8 25 Question 19 1 Question 20 3 Question 21 4 Question 22 2 Question 23 3 Question 24 2 Question 25 2 Question 26 1 Question 27 2 Question 28 2 Question 29 4 Question 30 1 Question 31 4 Question 32 2 Question 33 1 Question 34 2 Question 35 4 Solution for Question 1: Option B: Primary oocyte Primary oocytes are formed from primordial germ cells. In the ovaries, the primary oocyte gets arrested in diplotene by the fifth month in utero. Each primary oocyte remains at this stage until the period before ovulation up to menopause. Page 9 26 The hormonal changes in the young woman stimulate the ovarian and menstrual cycles, 5 to 15 oocytes will then begin maturation with each ovarian cycle throughout the woman’s reproductive life. Option A: Primordial germ cell A primordial germ cell is isolated from Epiblasts at the end of week 2nd of embryonal development and migrates to the endodermal wall of yolk sac In week 4, migration towards the genital ridge starts and completes at the end of week 5 to form gametes. Primordial germ cell undergoes continuous mitotic divisions to form the primary oocyte. Primordial germ cells sometimes abnormally migrate to neck region causing Craniopharyngeal teratoma. Option C: Secondary oocyte During puberty, at the time of ovulation, meiosis I completed, and the primary oocyte is converted to a secondary oocyte and first polar body. The secondary oocyte is arrested in Metaphase II [meiosis II] till fertilization. After fertilization, the second polar body and ovum are released. Oocytes are protected by granulosa cells, and those not protected undergo atresia Option D: First polar body During puberty, at the time of ovulation, meiosis I completed, and the primary oocyte is converted to a secondary oocyte and first polar body. After fertilization, the second polar body and ovum are released. Solution for Question 2: Option B: Metanephrons Urogenital sinus forms pronephros, mesonephros, metanephros Kidney develops from metanephros Pronephros gets degenerated Establishment of the metanephric kidney is preceded by the formation of two other mesenchyme-derived kidney-like structures: The pronephros and the mesonephros. Both are transient kidney-like paired structures that do not contribute to the permanent kidney. Option A: Ureteric bud Kidney develops from metanephros Mesonephric duct gives rise to the ureteric bud Ureteric bud stimulates metanephros to form the kidney Option C: Mesonephrons Mesonephros leaves behind mesonephric duct and degenerates Mesonephric duct gives ureteric bud Page 10 27 Ureteric bud stimulates metanephros to form the excretory component of the kidney. Option D: None of the above Establishment of the metanephric kidney is preceded by the formation of two other mesenchyme-derived kidney-like structures: Pronephros and the mesonephros. Solution for Question 3: Option A: 2 only The mesoderm divides into intermediate mesoderm, paraxial mesoderm, and lateral plate mesoderm. The post-otic part of the paraxial mesoderm forms a solid bilateral cord of cells extending along the side of the notochord beneath the neural tube. It undergoes segmentation to form a series of paired somites. The intermediate mesoderm forms the kidneys and the gonads. The lateral plate mesoderm forms the pleura, peritoneum, and pericardium. The somites further divide into the ventromedial sclerotome and the dorsolateral dermomyotome. Sclerotome on each side forms half of the vertebrae, which fuse to form the vertebral column. The myotome forms the skeletal muscles, and the dermatome forms the skin. The somites first appear at 20th day. Then a pair is added after every three days The somites appear between 20-30 days of development, and by the end of the first month, 44 pairs of somites are laid down. Thus, the 4th week of development is known as the somite period. Out of 44 pairs of post-otic somites, 4 are occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 8-12 coccygeal. Option B: 2 & 3 only The somites are differentiated into the ventromedial sclerotome and the dorsolateral part that forms the dermomyotome. Statement 3 in the question is true about the somites. Option C: 2, 3 & 4. Statements 3 and 4 are true about somites. The somites appear between 20-30 days of development, and by the end of the first month, 44 pairs of somites are laid down. Solution for Question 4: Option B: Paraxial mesenchyme Mesoderm is divided into paraxial mesoderm, intermediate mesoderm, and lateral plate mesoderm. The paraxial mesoderm differentiates into the somites. Somites further divide into the ventromedial sclerotome and the dorsolateral dermomyotome. The sclerotome forms the vertebrae, ribs, tendons, and vertebral joints. The myotome forms the skeletal muscles, whereas the dermatome forms the skin. Page 11 28 The intermediate mesoderm forms the kidneys and the gonads (testes and ovaries). The dorsal somatic lateral plate mesoderm will form the parietal layers of the peritoneum, pleura, and pericardium. At the same time, the ventral visceral plate mesoderm (splanchnic lateral plate mesoderm) forms visceral layers of the peritoneum, pleura, and pericardium. Option A: Endothoracic fascia Endothoracic fascia is a layer of loose connective tissue between the pleura and the ribs. The dorsal somatic lateral plate mesoderm forms it. Option C: Lateral plate mesoderm The lateral plate mesoderm is formed by the lateral most of the mesoderm. It divides into a dorsal somatic layer and a ventral visceral layer, forming the pleura, peritoneum, and pericardium. Option D: Superficial intercostal fascia It is an incorrect option. The dermatome division of the somites forms it. Solution for Question 5: Option B: Ectoderm + Endoderm The buccopharyngeal membrane derived from ectoderm + endoderm represents the future opening of the oral cavity. Cells from epiblast invaginate to form primitive streaks, giving rise to ectoderm and endoderm. The primitive streak has 3 parts Primitive groove Primitive Knot Primitive Pit Primitive groove Primitive Knot Primitive Pit As epiblast cells proliferate to form primitive streaks, some epiblast cells jump into the primitive pit and go ventrally to replace hypoblast cells with endoderm. Ectoderm and endoderm fuse at some level towards the cephalic end, forming the buccopharyngeal membrane and the caudal end, forming the cloacal membrane Primitive groove Primitive Knot Primitive Pit Options A , C, D Ectoderm and endoderm fuse towards the cephalic end, forming the buccopharyngeal membrane, and the caudal end, forming the cloacal membrane. Both membranes do not have mesoderm because of the fusion of the dorsal ectoderm with the ventral endoderm. Page 12 29 Solution for Question 6: Option B: Kidneys The mesoderm is the germ layer between ectoderm and endoderm and is divided into many segments. These segments are intermediate mesoderm, lateral plate mesoderm, and paraxial mesoderm. The intermediate mesoderm is the subdivision of the intraembryonic mesoderm that forms a longitudinal dorsal ridge called the urogenital. The intermediate mesoderm gives a major portion of the genitourinary system, mainly kidneys, testes and ovaries. It also forms smooth muscles of the genitourinary system. Option A: Urethra The endoderm of the Urogenital sinus forms the epithelium of the urinary bladder, urethra, and lower vagina. Option C: Peritoneal cavity The peritoneal cavity is derived from the lateral plate mesoderm. Option D: Somites The somites develop from the paraxial mesoderm. Somites are composed of the sclerotome, myotome, and dermatome that form the vertebrae, skeletal muscles, and skin. Solution for Question 7: Option A: Neural crest cells Page 13 30 Hirschsprung disease is associated with RET mutations. This mutation leads to the failure of neural crest cell migration. The patient presents with bilious emesis, abdominal distension, and failure to pass meconium in 48 hours. Nerves of pharyngeal cleft – Pretrematic nerve (Pretrematic nerves run along the caudal border of the arch); Eg: chorda tympani, a tympanic branch of the glossopharyngeal nerve. Ganglia are derived from neural crest cells. Thus, nerves of pharyngeal clefts are derived from Neural crest cells. Option B: Mesoderm Mesoderm is not associated with Hirschsprung disease. Option C: Neural plate ectoderm It is not associated with Hirschsprung disease. Option D: Notochord Notochord or axial mesoderm stimulates the ectoderm of the nervous system; the Neural tube later forms the spinal cord. Vertebrae protect the spinal cord. Vertebrae are formed by the somite, which is divided into specific components; one of them is the sclerotome. This is not associated with Hirschsprung disease. Solution for Question 8: Option D: Arrector Pilorum The patient has been diagnosed with Sheehan syndrome This is a syndrome where pituitary becomes double its size, and the blood supply cannot compensate, leading to ischemia. The patient presents with an inability to lactate, fatigue, and loss of pubic hair in the early postpartum period. Anterior pituitary develops from oral ectoderm. The lateral plate mesoderm has two components Dorsal Somatic lateral plate mesoderm and the Ventral visceral lateral plate mesoderm. Ventral Visceral Mesoderm derivatives are Visceral layers of Pleura, Peritoneum, and Pericardium. Visceral Muscles, Cardiac muscles, CV tube, Smooth muscles, Gut tube, and RespiratoryTube. Arrector Pilorum is a Smooth muscle in the skin. Derived from Mesenchyme Option A: Epidermis Surface ectoderm derivatives include Epithelium and glands Skin epithelium Epithelium and glands Skin epithelium Epithelium and glands Skin epithelium Page 14 31 Option B: Parotid gland Surface ectoderm derivatives also include Rathke's pouch (most of the pituitary gland) Salivary glands Parotid, submandibular, and sublingual glands Rathke's pouch (most of the pituitary gland) Salivary glands Parotid, submandibular, and sublingual glands Rathke's pouch (most of the pituitary gland) Salivary glands Parotid, submandibular, and sublingual glands Option C: Neurohypophysis Neural plate ectoderm derivatives Iris muscles: Sphincter and dilator pupillae CNS Neurohypophysis(posterior pituitary gland) Iris muscles: Sphincter and dilator pupillae CNS Neurohypophysis(posterior pituitary gland) Iris muscles: Sphincter and dilator pupillae CNS Neurohypophysis(posterior pituitary gland) Solution for Question 9: Option B: CNS defects DiGeorge syndrome is also known as 22q11.2 deletion syndrome. Infants with DiGeorge syndrome are born without a thymus and parathyroid glands and have defects and cardiac outflow tracts. It occurs due to failure of third and fourth pharyngeal pouches differentiation. This results from a breakdown in signaling between pharyngeal endoderm and adjacent neural crest cells. It includes:- Cardiac defects Pharyngeal arch bone defects Skull defects And hypoparathyroidism and immunodeficiency due to the absence of the thymus. CNS defects are not part of DiGeorge syndrome. Cardiac defects Pharyngeal arch bone defects Skull defects And hypoparathyroidism and immunodeficiency due to the absence of the thymus. CNS defects are not part of DiGeorge syndrome. Cardiac defects Page 15 32 Pharyngeal arch bone defects Skull defects And hypoparathyroidism and immunodeficiency due to the absence of the thymus. CNS defects are not part of DiGeorge syndrome. Option A: Skull defects Cleft lip and palate, nasal dermoid, ethmoid encephalocele are seen. Option C: Pharyngeal arch bone defects Pharyngeal arch bone defects by having small mandible (Hypognathia) is seen. Option D: Cardiac defects Aortic and pulmonary septum anamolies are seen and the main cause of death in DiGeorge syndrome from the cardiovascular system. Solution for Question 10: Option C: Pharyngeal arch muscles This patient is suffering from oculocutaneous albinism. Due to a defect in an enzyme, there is a decrease in the production of melanin. Melanin is produced from melanocytes. Melanocytes are derived from neural crest cells. The somite derivative of the mesoderm includes; Dermatome [lateral part] → skin dermis Myotome [middle part] → skeletal muscles (on each side forms half of the vertebrae) Sclerotome [medial part], → bone [on each side forms half of the vertebrae]. The sclerotome on each side forms half of the vertebrae, which fuse to form complete vertebrae. Myotome mainly forms muscle (skeletal muscle), and Dermatome forms dermis (skin). Dermatome [lateral part] → skin dermis Myotome [middle part] → skeletal muscles (on each side forms half of the vertebrae) Sclerotome [medial part], → bone [on each side forms half of the vertebrae]. The sclerotome on each side forms half of the vertebrae, which fuse to form complete vertebrae. Myotome mainly forms muscle (skeletal muscle), and Dermatome forms dermis (skin). So pharyngeal arch muscles are a derivative of the somite mesoderm. They are not developed from neural crest cells Dermatome [lateral part] → skin dermis Myotome [middle part] → skeletal muscles (on each side forms half of the vertebrae) Sclerotome [medial part], → bone [on each side forms half of the vertebrae]. The sclerotome on each side forms half of the vertebrae, which fuse to form complete vertebrae. Myotome mainly forms muscle (skeletal muscle), and Dermatome forms dermis (skin). Option A: Pharyngeal arch bones Neural crest cell derivatives are peripheral nervous system [includes ganglia], Secondary Mesenchyme/ Mesoderm, and Most of the skull bones [head & neck anterior & lateral regions], Page 16 33 Most eyeball mesoderm, Pharyngeal arch bones [malleus, incus, stapes, mandible, hyoid bones], Aorta pulmonary septum, The dermis of head & neck and odontoblasts. Option B: Dermis of head and neck Neural crest cell (4th germ layer) derivatives include PNS (includes ganglia), secondary mesenchyme/ mesoderm - most of the skull bones (head and neck anterior and lateral regions), most of the eyeball mesoderm, pharyngeal arch bones, aorta pulmonary septum the dermis of the head and neck and odontoblasts. Option D: Odontoblasts Neural crest cell (4th germ layer) derivatives include PNS (includes ganglia), secondary mesenchyme/ mesoderm - most of the skull bones (head and neck anterior and lateral regions), most of the eyeball mesoderm, pharyngeal arch bones, aorta pulmonary septum the dermis of the head and neck and odontoblasts. Hence it is the incorrect option. Solution for Question 11: Option D: Detrusor Somites are the component of paraxial mesoderm which form the sclerotome, dermatome, and myotome that includes the skeletal muscles The detrusor is the smooth muscle of the genitourinary system. The detrusor is derived from the intermediate mesoderm that includes kidneys (pronephros, mesonephros, metanephros), gonads, and renal and genital excretory ducts. Option A: Masseter Somite derivatives components are Dermatome [lateral part] → Skin Dermis, Myotome [middle part] → Skeletal Muscles Sclerotome [medial part] → Bone [vertebra]. Dermatome [lateral part] → Skin Dermis, Myotome [middle part] → Skeletal Muscles Sclerotome [medial part] → Bone [vertebra]. The myotome includes the master muscle that is responsible for the action of mastication. Since the masseter is a skeletal muscle, it is a derivative of the paraxial mesoderm (somites). Dermatome [lateral part] → Skin Dermis, Myotome [middle part] → Skeletal Muscles Sclerotome [medial part] → Bone [vertebra]. Option B: Diaphragm Among somite derivatives, the diaphragm is a part of the myotome (skeletal muscle mostly) that plays a role in breathing. The diaphragm is also a skeletal muscle derivative of the paraxial mesoderm. Option C: Biceps femoris The biceps femoris is a skeletal muscle that's primary function is flexion of the knee. Page 17 34 It is a derivate of paraxial mesoderm that includes skeletal muscles. Solution for Question 12: Option C: Smooth muscles of the gut tube The parietal/ somatopleuric layer of lateral plate mesoderm forms appendicular skeleton Visceral layers of the peritoneum, pleura, and pericardium, Visceral muscles- cardiac muscles of the cardiogenic area, smooth muscles of the gut tube and respiratory tube Visceral layers of the peritoneum, pleura, and pericardium, Visceral muscles- cardiac muscles of the cardiogenic area, smooth muscles of the gut tube and respiratory tube So, Smooth muscles of the gut tube arise from the visceral splanchnic lateral plate mesoderm. Visceral layers of the peritoneum, pleura, and pericardium, Visceral muscles- cardiac muscles of the cardiogenic area, smooth muscles of the gut tube and respiratory tube Option A: Myoepitheliocytes of skin glands Myoepitheliocytes of skin glands is a derivative of the surface ectoderm. The surface ectoderm derivatives are Epithelium: Skin epithelium Glands: Sweat glands, Sebaceous glands, myoepitheliocytes of skin glands, and any external openings. Epithelium: Skin epithelium Glands: Sweat glands, Sebaceous glands, myoepitheliocytes of skin glands, and any external openings. This is an exception when coming to the derivative of the visceral layer, which forms from mesoderm. Epithelium: Skin epithelium Glands: Sweat glands, Sebaceous glands, myoepitheliocytes of skin glands, and any external openings. Option B: Iris muscles. Iris muscle is a derivative of neural plate ectoderm. It is also an exception because it is a visceral layer of muscle. Neural plate ectoderm derivatives are Iris muscles: Sphincter pupillae, dilator pupillae CNS Neurohypophysis, down word extension of the diencephalon Iris muscles: Sphincter pupillae, dilator pupillae CNS Neurohypophysis, down word extension of the diencephalon As Iris muscle is derivative of ectoderm, not the visceral mesoderm. Iris muscles: Sphincter pupillae, dilator pupillae CNS Neurohypophysis, down word extension of the diencephalon Page 18 35 Option D: Detrusor The detrusor muscle is a derivative of an intermediate mesoderm, not the lateral mesoderm. Axial mesoderm is a notochord that forms the nucleus pulposus in the intervertebral disc later. Paraxial mesoderm will form the somite. The intermediate mesoderm will form the kidney, testes, and ovary, a major portion of the genitourinary system. So, the detrusor is not a part of the lateral mesoderm. Solution for Question 13: Option C: Surface ectoderm The marked structure is the lens and it develops from Surface ectoderm This patient with features of tall stature, long slender hands, and upward and outward displacement of lens is diagnosed with Marfan's syndrome. Epiblast cells that are lying on the floor of the amniotic cavity undergo proliferation to form a primitive streak. The primitive streak has 3 parts Primitive groove Primitive Knot Primitive Pit Primitive groove Primitive Knot Primitive Pit As epiblast cells proliferate to form primitive streak, some epiblast jumps into primitive pit and they go ventrally to replace hypoblast cell into endoderm. Endoderm is more ventral; the dorsal layer in the middle known as mesoderm formed by epiblast cells. Epiblast in the dorsal will form a surface ectoderm. The lens develops from the surface ectoderm. The cornea is also a derivative of surface ectoderm Primitive groove Primitive Knot Primitive Pit Option A: Endoderm No part of the eye is develops from the endoderm Endoderm derivatives are Gut tube epithelium Lower vagina Most parts of the urethra Luminal epithelial derivatives (liver, gall bladder, lungs, pancreas, thymus, eustachian tube, parafollicular cells of thyroid, parathyroid) Gut tube epithelium Lower vagina Most parts of the urethra Luminal epithelial derivatives (liver, gall bladder, lungs, pancreas, thymus, eustachian tube, parafollicular cells of thyroid, parathyroid) Page 19 36 Gut tube epithelium Lower vagina Most parts of the urethra Luminal epithelial derivatives (liver, gall bladder, lungs, pancreas, thymus, eustachian tube, parafollicular cells of thyroid, parathyroid) Option B: Mesoderm Secondary mesoderm derivatives contributing to the structure of the eye are: Connective tissue All layers of cornea except 1st layer Vitreous Sclera, choroid Dura mater Connective tissue All layers of cornea except 1st layer Vitreous Sclera, choroid Dura mater Connective tissue All layers of cornea except 1st layer Vitreous Sclera, choroid Dura mater Option D: Neuroectoderm The derivatives of neuro ectoderm are as follows: Iris muscles Sphincter pupillae Dilator pupillae Sphincter pupillae Dilator pupillae CNS Neurohypophysis Downward extension of the diencephalon Downward extension of the diencephalon Sphincter pupillae Dilator pupillae Downward extension of the diencephalon Solution for Question 14: Option B: Motor neurons Motor neurons develop from neural tube (Neural plate ectoderm), hence may not be affected in dysgenesis of neural crest cells. Neural crest (also called 4th germ layer) derivatives are: Peripheral nervous system [includes ganglia] Most of the skull bones [head & neck anterior & lateral regions]. Pharyngeal arch bones Page 20 37 [malleus, incus, stapes, mandible, hyoid bones] Aorticopulmonary septum Dermis of head and neck Melanocytes Tracheal lining Enterochromaffin cells Adrenal medulla Leptomeninges Schwann cells Endocardial cushions Odontoblast Peripheral nervous system [includes ganglia] Most of the skull bones [head & neck anterior & lateral regions]. Pharyngeal arch bones [malleus, incus, stapes, mandible, hyoid bones] Aorticopulmonary septum Dermis of head and neck Melanocytes Tracheal lining Enterochromaffin cells Adrenal medulla Leptomeninges Schwann cells Endocardial cushions Odontoblast Peripheral nervous system [includes ganglia] Most of the skull bones [head & neck anterior & lateral regions]. Pharyngeal arch bones [malleus, incus, stapes, mandible, hyoid bones] Aorticopulmonary septum Dermis of head and neck Melanocytes Tracheal lining Enterochromaffin cells Adrenal medulla Leptomeninges Schwann cells Endocardial cushions Odontoblast Page 21 38 Option A: Melanocytes Melanocytes are derivatives of neural crest cells. The deficiency of melanocytes results in albinism and vitiligo. Option C: Parafollicular cells Parafollicular or C cells are derived from neural crest cells that fuse with the thyroid gland. These cells are distributed throughout the thyroid gland to secrete, synthesize calcitonin, and store it. Option D: Spinal ganglion cells Spinal ganglion cells are part of cranial and truncal neural crest cells. Solution for Question 15: Option C: 480 Page 22 39 During puberty, at the time of ovulation, meiosis I completed, and the primary oocyte is converted to a secondary oocyte and first polar body. After fertilization, the second polar body and ovum are released. A mature ovum is released from the ovary during ovulation. During her reproductive period, a woman will ovulate approximately 480 ova. A woman will ovulate 12 primary ova per year as long as she is not taking oral contraceptives, does not become pregnant, or does not have any anovulatory cycle. Assuming that a reproductive time of 40 years gives 40 x12 = 480 ova. Option A: 40,000 The hormonal changes in the young woman stimulate the ovarian and menstrual cycles; 5 to 15 oocytes will then begin maturation to form ova with each ovarian cycle throughout the woman’s reproductive life. All of the ova (40000) don't ovulate during the entire reproductive age. Option B: 35,000 Most of the ovum doesn’t ovulate during the entire reproductive age, as a woman will ovulate approximately 480 ova. Option D: 48 Although, all ovum do not ovulate during the entire reproductive age. Approximately 480 ova will be ovulated, whereas the number of 48 is significantly few. Solution for Question 16: Option A: Crossing over The process of genetic recombinations between two homologous chromosomes occurs during the Prophase-I of Meiosis-I. Page 23 40 Prophase-I is a complex phase entirely different from the mitotic prophase and is divided into five phases. Leptotene is the first phase where homologous chromosomes (maternal and paternal copies of the same chromosomes) begin to condense. Zygotene is the phase during which homologous chromosomes start pairing. This process of pairing is called synapsis. The homologous chromosome pairs are called Bivalent (two chromosomes) or Tetrad (having 4 chromatids). Synapsis is necessary for the exchange of DNA segments to occur during crossing-over. During Pachytene, the synapsis is complete for all chromosomes. During this phase, DNA segments are exchanged between two non-sister chromatids (chromatids belonging to different chromosomes) in a process known as crossing over. The point on homologous chromosomes where crossing over occurs is called chiasmata. Diplotene occurs after the crossing over of chromosomes. During this phase, pairs of homologous chromosomes separate except where crossing over has occurred (chiasmata). This process is called a disjunction. In the ovaries, primary oocytes get arrested in diplotene during the fifth month in utero, and each remains at this stage until the period before ovulation (up to 50 years). Diakinesis is the prometaphase of the first meiotic division. The condensation of homologous chromosomes reaches its maximum, and the nuclear membrane disintegrates, which starts the next process, i.e., Metaphase-I. Leptotene is the first phase where homologous chromosomes (maternal and paternal copies of the same chromosomes) begin to condense. Zygotene is the phase during which homologous chromosomes start pairing. This process of pairing is called synapsis. The homologous chromosome pairs are called Bivalent (two chromosomes) or Tetrad (having 4 chromatids). Synapsis is necessary for the exchange of DNA segments to occur during crossing-over. During Pachytene, the synapsis is complete for all chromosomes. During this phase, DNA segments are exchanged between two non-sister chromatids (chromatids belonging to different chromosomes) in a process known as crossing over. The point on homologous chromosomes where crossing over occurs is called chiasmata. Diplotene occurs after the crossing over of chromosomes. During this phase, pairs of homologous chromosomes separate except where crossing over has occurred (chiasmata). This process is called a disjunction. In the ovaries, primary oocytes get arrested in diplotene during the fifth month in utero, and each remains at this stage until the period before ovulation (up to 50 years). Diakinesis is the prometaphase of the first meiotic division. The condensation of homologous chromosomes reaches its maximum, and the nuclear membrane disintegrates, which starts the next process, i.e., Metaphase-I. Leptotene is the first phase where homologous chromosomes (maternal and paternal copies of the same chromosomes) begin to condense. Zygotene is the phase during which homologous chromosomes start pairing. This process of pairing is called synapsis. The homologous chromosome pairs are called Bivalent (two chromosomes) or Tetrad (having 4 chromatids). Synapsis is necessary for the exchange of DNA segments to occur during crossing-over. During Pachytene, the synapsis is complete for all chromosomes. During this phase, DNA segments are exchanged between two non-sister chromatids (chromatids belonging to different chromosomes) in a process known as crossing over. The point on homologous chromosomes where crossing over occurs is called chiasmata. Diplotene occurs after the crossing over of chromosomes. During this phase, pairs of homologous chromosomes separate except where crossing over has occurred (chiasmata). This process is called a disjunction. In the ovaries, primary oocytes get arrested in diplotene during the fifth month in utero, and each remains at this stage until the period before ovulation (up to 50 years). Page 24 41 Diakinesis is the prometaphase of the first meiotic division. The condensation of homologous chromosomes reaches its maximum, and the nuclear membrane disintegrates, which starts the next process, i.e., Metaphase-I. Option B: Nondisjunction: This occurs during anaphase of meiosis when the pair of homologous chromosomes fail to segregate. This leads to the formation of gametes with one chromosome extra or less than the average number. Examples include Down's syndrome, Turner syndrome, and Klinefelter's syndrome. Option C: Alignment The sequencing of two or more protein or nucleic acid chains to check the similarity of their amino acids is used to compare the identity of one protein to others and evaluate the conservation of evolution. Option D: Synapsis Synapsis is the pairing of homologous chromosomes that occurs only during meiosis I in the production of gametes. It takes place during the Zygotene phase. Solution for Question 17: Option D: Metaphase of meiosis II Oogenesis (development of oocytes) starts before birth in females. The primordial germ cell (oogonium) undergoes several mitotic divisions to form primary oocytes. Primary oocytes are arrested in the diplotene stage of the prophase of Meiosis I. This arrest in development occurs due to the action of an oocyte maturation inhibitor (OMI) that increases the levels of cyclic AMP. The increased cyclic AMP levels lead to the inactivation of proteins responsible for cell division. After puberty, secondary oocytes are formed from primary oocytes due to the LH surge. This LH surge at puberty reduces cyclic AMP levels and resumes the development of oocytes. The secondary oocyte is arrested in the metaphase of meiosis II about 3 hours before ovulation. It remains in this meiotic stage until fertilization occurs. The fusion of sperm with the secondary oocyte is the stimulus for the completion of meiosis, and the formation of the egg occurs. Option A: Prophase of meiosis I. The primary oocyte is arrested in the diplotene phase of meiosis-I. After puberty, the arrested primary oocytes undergo the completion of meiosis-I and are arrested in the metaphase of meiosis II until fertilization occurs. Option B: Prophase of meiosis II. The prophase of meiosis II is similar to the prophase of mitosis. Oocytes are not arrested in any stage of their development during the prophase of meiosis II. Option C: Metaphase of meiosis I. Oocytes do not arrest during the metaphase of meiosis I. After puberty, they start dividing until they become arrested in metaphase II of meiosis. Page 25 42 Solution for Question 18: Option A: Primary yolk sac Extra-embryonic mesoderm is formed by the cell lining of the primary yolk sac. Primary yolk sac > caudal region of the epiblast > parietal hypoblast > trophoblast. The extra-embryonic mesoderm is divided into two parts One towards the yolk sac is called visceral or splanchnopleuric extra-embryonic mesoderm. Beyond that lines, the amniotic cavity and outside are called the parietal or somatopleuric extra-embryonic mesoderm towards the body wall. One towards the yolk sac is called visceral or splanchnopleuric extra-embryonic mesoderm. Beyond that lines, the amniotic cavity and outside are called the parietal or somatopleuric extra-embryonic mesoderm towards the body wall. Between the somatopleuric and splanchnopleuric extra-embryonic mesoderm, there is the extra-embryonic coelomic cavity. One towards the yolk sac is called visceral or splanchnopleuric extra-embryonic mesoderm. Beyond that lines, the amniotic cavity and outside are called the parietal or somatopleuric extra-embryonic mesoderm towards the body wall. Option B: Secondary yolk sac During the division, cells from the mesoderm pinch off an area of the yolk sac; the remaining structure is called the secondary yolk sac. Option C: Epiblast Embryoblast consists of Hypoblast: Ventral, degenerate and contributes to extra-embryonic structures Epiblast: Dorsal columnar cells in the inner cell mass Amniotic cavity Yolk sac cavity Hypoblast: Ventral, degenerate and contributes to extra-embryonic structures Epiblast: Dorsal columnar cells in the inner cell mass Amniotic cavity Yolk sac cavity Although the extra-embryonic mesoderm is formed from the caudal part of the epiblast, option A is the more appropriate choice. Hypoblast: Ventral, degenerate and contributes to extra-embryonic structures Epiblast: Dorsal columnar cells in the inner cell mass Amniotic cavity Yolk sac cavity Option D: Hypoblast Hypoblast is a ventral structure of embryoblast. It degenerates and contributes to the formation of extra-embryonic structures. Page 26 43 Solution for Question 19: Option A: Primary umbilical cord The extraembryonic coelomic cavity is between the somatopleuric extraembryonic and visceral/splanchnic mesoderm. A somatopleuric layer of extraembryonic mesoderm with trophoblast form chorion. Amnion is formed by angiogenic cells lining the amniotic cavity and somatopleuric layer of the extraembryonic mesoderm. Connecting stalk is a precursor of the umbilical cord. It includes the allantois and vitelline ducts that form the primary umbilical cord. Option B: Secondary umbilical cord The secondary umbilical cord is not known to form by connecting stalk. Option C: Decidua parietalis The maternal placenta has three layers. Decidua basalis Decidua capsularis Decidua parietalis Decidua basalis Decidua capsularis Decidua parietalis Decidua basalis is the endometrium where the embryo implants and forms the maternal /uterine placenta, while decidua capsularis surrounds the embryo on the luminal side and doesn't form the placenta. Decidua parietalis forms the rest of the gravid endometrium, not the mesoderm part forming connecting stalk. Decidua basalis Decidua capsularis Decidua parietalis Option D: Decidua capsularis Decidua capsularis surrounds the embryo on the luminal side and doesn’t form the placenta. It is not related to connecting the stalk that forms the umbilical cord. Solution for Question 20: Option C: Day 17 During the second week of pregnancy, the rapid proliferation of chorion forms finger-like projections called chorionic villi. They are meant to increase the surface area of the placenta essential for nutrients transfer from maternal blood to the fetus. Primary chorionic villi are non-vascular that contain trophoblasts and are formed during 13 to 15 days of gestation. Page 27 44 Secondary chorionic villi contain trophoblasts and mesoderm formed during 16 to 21 days of gestation. Tertiary chorionic villi contain trophoblasts, mesoderm, and blood vessels derived from the umbilical artery and vein. They are formed between days 17 to 22. Solution for Question 21: Option D: Central fetal blood vessels surrounded by mesoderm and trophoblast. The embryo implants at the endometrium on day 5 or 6 after fertilization. The blastocyst forms the outer trophoblastic cells and the inner embryoblast cells. The outer trophoblast cells divide into cytotrophoblasts and syncytiotrophoblasts that are responsible for attaching the embryo to the endometrium of the mother (decidua basalis) The syncytiotrophoblast cells grow into the decidua basalis and cytotrophoblast cells to form primary villi. The primary villi are formed on the 12th day. After forming the primary villi, extraembryonic mesoderm cells migrate into the spaces formed by the trophoblastic cells. This forms the secondary villi containing a central core of extraembryonic mesoderm covered by cytotrophoblast and syncytiotrophoblast cells. At day 17, fetal blood cells start growing into the secondary villi, forming tertiary villi. Hence the tertiary villi contain fetal blood vessels invading the extraembryonic mesoderm and are covered by trophoblastic cells. During development, the maternal spiral arteries pass through the decidual plate to enter the junctional zone where the maternal and fetal blood is in cavities. This forms the maternal contribution of the placenta. The chorionic plate from the fetus forms the chorionic frondosum consisting of the chorionic villi. This forms the fetal contribution of the placenta. Option A: Central core of cytotrophoblast covered with syncytiotrophoblast A central core of cytotrophoblasts covered with syncytiotrophoblasts forms the primary villi, not the tertiary villi. Option B: Central core of extraembryonic mesoderm covered by central cytotrophoblasts and perip heral syncytiotrophoblasts Secondary villi contain a central core of primary (extraembryonic) mesoderm and are covered by cytotrophoblast and syncytiotrophoblast cells. This question is about the tertiary villi. Option C: Central maternal blood vessels surrounded by mesoderm and trophoblast The maternal spiral arteries are from the maternal side of the placenta, not the chorionic villi formed by the fetus. Solution for Question 22: Option B: Cuboidal endodermal cells Page 28 45 During week 3 of development after the formation of syncytio trophoblast, the other cells in 6-8 days divide to form: Dorsal epiblast (floor of amniotic cavity)- cells are columnar. Ventral hypoblast (at the roof of the yolk sac cavity)- cells are cuboidal endodermal Dorsal epiblast (floor of amniotic cavity)- cells are columnar. Ventral hypoblast (at the roof of the yolk sac cavity)- cells are cuboidal endodermal Epiblast cells will migrate towards the ventral side, to display the hypoblast cells to take their space for becoming endoderm (first germ layer). These hypoblasts cells are removed by the epiblasts, they will be lining the yolk sac cavity (forming extra embryonic endoderm). Embryonic endoderm is formed by the epiblast cells. The secondary yolk sac is lined by cuboidal endodermal cells. Dorsal epiblast (floor of amniotic cavity)- cells are columnar. Ventral hypoblast (at the roof of the yolk sac cavity)- cells are cuboidal endodermal Epiblast cells will migrate towards the ventral side, to display the hypoblast cells to take their space for becoming endoderm (first germ layer). These hypoblasts cells are removed by the epiblasts, they will be lining the yolk sac cavity (forming extra embryonic endoderm). Embryonic endoderm is formed by the epiblast cells. The secondary yolk sac is lined by cuboidal endodermal cells. Option A: Flattened endodermal cells Initially, the primary yolk sac is formed by the proliferation of hypoblast cells, which then undergo maturation into the secondary yolk sac. This primary yolk sac is lined by flattened endodermal cells Option C: Extra-embryonic mesoderm The extra-embryonic mesoderm is derived from the hypoblast cells. It protects and supports the amniotic epithelium and the yolk sac. It also forms the villi and also forms the chorionic cavity. Option D: None of the above This option is incorrect as the secondary yolk sac is lined by cuboidal epidermal cells. Solution for Question 23: Option C: It mostly arises from the 2nd pharyngeal arch A branchial cyst is the remnant of the embryological second branchial cleft or cervical sinus, which normally regresses before birth. It is located lateral to the midline and does not move with deglutition. 95% of all branchial cleft malformations are anomalies of the second branchial cleft. It is usually diagnosed in late childhood or adulthood. Page 29 46 It is mostly asymptomatic. When symptomatic, it leads to recurrent upper respiratory tract infections. It is treated with antibiotics when infected, but if medical management fails, it can be surgically excised. Option A: It causes dysphagia and hoarseness A branchial cyst is mostly asymptomatic. When infected, it presents with painful swelling, erythema, and fever, but there is no dysphagia and hoarseness. Option B: It should always be operated. Branchial cysts are usually asymptomatic. Therefore, no treatment is needed. If it gets infected, antibiotics are used first. Surgical excision is used when antibiotics fail or due to cosmetic reasons. Option D: It moves with deglutition Branchial cyst does not move with deglutition. The Thyroglossal duct cyst moves with deglutition as it is attached to the tongue. Solution for Question 24: Option B: Prostatic utricle Paramesonephric ducts develop from mesoderm by the end of the 8th week. In the embryo, these ducts drain the primitive kidneys. In females, these are precursors to the internal sex organs. Their differentiation is driven by estrogens and suppressed by Mullerian Inhibiting Factor. In males, these ducts regress and form some vestigial organs. They form prostatic utricles in males. The prostatic utricle is a small, blind, sac-like, midline pouch in the prostatic urethra. It is flanked by the openings of the ejaculatory duct. Option A: Trigone of bladder Mesonephric ducts develop from mesoderm by the end of the 6th week. These ducts give rise to the ureteric bud, stimulating metanephros to develop into kidneys. The tip of the mesonephric duct is absorbed into the posterior wall of the urogenital sinus and forms the trigone of the urinary bladder. Options C: Paroophoron The mesonephric ducts in males form most of the internal sex organs, but in females, they undergo regression. They form vestigial organs in females, including epoophoron, paroophoron, and Gartner's duct. Page 30 47 Epoophoron is usually found between the ovary and fallopian tissue. Paroophoron is found in the mesosalpinx below the epoophoron. Option D: Gartner's duct Gartner's duct is formed by the mesonephric duct, not the paramesonephric duct. Gartner duct cysts are located in the anterolateral wall of the proximal (superior) portion of the vagina. Solution for Question 25: Option B: Surface epithelium The specific cells mentioned here denote the Sertoli cells. A Sertoli cell (a kind of sustentacular cell) is a "nurse" cell of the testicles that is part of a seminiferous tubule and helps in the process of spermatogenesis, the production of sperm. These are columnar epithelial cells lining seminiferous tubules (non-germ cells). Their main function is to nourish the developing sperm cells through the stages of spermatogenesis. These cells are derived from the epithelial sex cords of the developing gonad These cells surround the germ cells in the seminiferous tubules and provide them with nutrients that help them in various stages of differentiation. Spermatogonia forms primary spermatocyte, which then forms secondary spermatocyte. These secondary spermatozoa form spermatids which then form spermatozoa. During all these stages of spermiogenesis, the Sertoli cells maintain the nutrition of and support the germ cells. Option A: Genital swelling Genital swelling develops from the dorsal somatic lateral plate mesoderm. In males, it forms the scrotum; in females, it forms the labia majora. Option C: Genital tubercle The genital tubercle is derived from the dorsal somatic lateral plate mesoderm. It forms the glans penis in males and the clitoris in females. Option D: Primordial germ cells Primordial germ cells can be isolated by the end of 2nd week from the primitive streak. These cells reach the endodermal wall of the yolk sac and later migrate to the genital ridge. Solution for Question 26: Option A: Lamina terminalis The right and the left halves of the hemispheres are connected by several fiber bundles called commissures. Page 31 48 The commissure that streamlines the flow of non-olfactory information across the two cerebral hemispheres of the brain is called the corpus callosum. It is essential for communication between the left and right hemispheres. The corpus callosum is a wide, thick nerve tract consisting of a flat bundle of commissural fibers beneath the cerebral cortex in the brain. Its development occurs between the 12th and 16-20th weeks of gestation from the lamina terminalis. The lamina terminalis also gives rise to the anterior commissure, which connects the two cerebral hemispheres and is involved in the transmission of non-olfactory information between them. The corpus callosum has four main parts; individual nerve tracts that connect different parts of the hemispheres. These are the rostrum, the genu, the trunk or body, and the splenium. Other commissures are anterior commissure, posterior commissure, habenular commissure, and hippocampal commissure. Option B: Basal plate The basal plate gives rise to the anterior and lateral horn cells. The anterior horn cells form the lower motor neuron fibers, which control the skeletal muscles of our body. The lateral horn cells form the sympathetic tracts of our body which control the cardiac and smooth muscles of the body. Basal plate does not contribute to the formation of the corpus callosum, which is more related to sensory and integrative functions. Option C: Alar plate The alar plate forms the posterior horn cells. These posterior horn cells form the sensory tracts of the body. These include spinothalamic tracts (pain, temperature) and the dorsal column tracts (fine touch, proprioception, vibration). Option D: B and C The basal plate and alar plate do not form the commissures. Hence, this option is incorrect. Solution for Question 27: Option B: Agenesis of the paramesonephric duct Agenesis of the paramesonephric duct, or Müllerian agenesis, results in an atretic uterus, cervix, and upper third of the vagina. Patients are asymptomatic until puberty when they present with primary amenorrhea. Development of secondary sexual characteristics normally occurs since the gonads are functional and the patient has a normal female karyotype. Option A: Failure of the Mullerian duct to recanalize Failure to recanalize the Müllerian ducts (paramesone

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