Q2 Biology PhoTau Midterm Past Paper PDF

Biology - Q2 Midterm Date of Exam: December 3, 2024 Coverage: LGs 7.0 - 8.0 LG 7.0 - Chromosome Structure & Karyotyping Structure of Eukaryotic Chromosomes 1) Genes - Information containing elements that store instructions to make and maintain a living organism. Genes a...

Biology - Q2 Midterm Date of Exam: December 3, 2024 Coverage: LGs 7.0 - 8.0 LG 7.0 - Chromosome Structure & Karyotyping Structure of Eukaryotic Chromosomes 1) Genes - Information containing elements that store instructions to make and maintain a living organism. Genes are DNA or RNA sequences found in eukaryotic cell nuclei. 2) Deoxyribonucleic Acid (DNA) - The genetic material of all living things. - Measures about 2 meters in total length. - Must be contained within a nucleus with a diameter of less than 10 μm (micrometers) - Considered as the blueprint of life as it directs all cellular activities, therefore, it must be inherited by all descendants of a parent cell. Figure 1: Genes are segments of DNA that constitute a chromosome. Chromosomal Levels of Organization 1) DNA - Each chromosome consists of a single long molecule of DNA. 3 Parts of the DNA: a) Sugar b) Phosphate Group c) Base Adenine (A) Guanine (G) Thymine (T) Base-Pairing Rule: Cytosine (C) A-T G-C 2) Nucleosome (6 x 11 nm flat disc) - Basic unit of a chromatin structure. - Consists of DNA and a core of chromosomal proteins called histones. Q How are Nucleosomes formed? Nucleosomes are formed when the DNA makes a 1.7 [147 bp (base pairs)] turn around an A octamer core composed of two units of each histone H2A, H2B, H3, and H4. 3) Histones - A family of small, positively charged proteins capable of interacting with negatively charged DNA. 5 Major Types of Histone Proteins: a) Linker Histones - H1 b) Core/Nucleosomal Histones - H2A, H2B, H3, and H4 4) 30-nm (nanometers) chromatin fiber - Initially called a solenoid. - Formed when nucleosomes are further packed on top of one another. - This second level of coiling is achieved by the assistance of H1 histones. H1 is bound to the DNA as it enters and exits the nucleosome. It pulls adjacent nucleosomes together into a repeating array. 5) Solenoid - A secondary chromatin structure that helps package eukaryotic DNA into the nucleus. 6) Scaffold - A nonhistone protein to which solenoids that are arranged in loops are attached. Scaffold Attachment Regions (SARs) - Special regions along the DNA where the scaffold binds. - Responsible for the additional supercoiling of the DNA into succeeding levels of organization. ❖ During the prophase of mitosis, chromosomes: (1) condense into structures of much greater width and (2) decrease in length with several folds, generating the condensed chromosomes observed during metaphase. 7) Condensed Chromatin Fibe (300-nm) - Formed when the 30-nm chromatin fiber is further folded into a series of looped domains. 8) Metaphase Chromatid (700-nm) - One of the longitudinal subunits of the metaphase chromosome. - Formed when the 300-nm chromatin fiber coils further. - The DNA assumes this particular organization during cell division. 9) Sister Chromatid ❖ This highly condensed structure (chromatid) during mitosis reverts to its decondensed and uncoiled state (chromatin) as it enters the interphase of the cell cycle after chromosome separation and cell division. ❖ As it progresses into the cell cycle, these chromatins that are dispersed throughout the nucleus become visible chromosomes once again.  Figure 2: DNA organization into chromosomes. Karyotyping - The process of sorting and identifying to detect changes in its shape, size, and gene positions Types of Chromosomes 1) Autosomes - Any chromosomes that are not sex chromosomes. 2) Sex Chromosomes - Responsible for determining the sex of an organism. (X or Y) ★ XX - Female ★ XY - Male Humans have 46 chromosomes in their somatic cells. 22 pairs are autosomes, while the 23rd pair is the sex chromosome. Karyotype - An ordered display or diagram of the full set of an organism’s chromosomes. These are arranged in homologous pairs wherein two chromosomes (except sex chromosomes) are paired with respect to size, shape number, and banding pattern. Allows us to determine the sex and detect any chromosomal abnormalities that are associated with inherited defects such as diseases and certain types of cancer.  Figure 3: Karyotypes of normal male and female Figure 4: Karyotypes with abnormalities; (a) has an extra chromosome while (b) lacks a chromosome As shown in Figure 4 above, the karyotypes have abnormalities that influence the development of organisms, especially us humans. Figure 4.A consists of 47 chromosomes (XXY) or known as the Klinefelter Syndrome while Figure 4.B on the other hand is called the Turner Syndrome since it only consists of 45 chromosomes (X). Characteristics of the 2 Abnormalities: 1) Klinefelter Syndrome Referred to as Intersexuality due to its ambiguous (47, XXY) sexual development Tall stature, long limbs, large hands/feet Has male genitalia and internal ducts but their testes are rudimentary and fail to produce sperm Female sexual development is not entirely suppressed 2) Turner Syndrome Short stature and cognitive impairments (45, X) Has female external genitalia and internal ducts but the ovaries are rudimentary Skin folds on the back of the neck and underdeveloped breasts. Other Abnormalities 1) Super Female Referred to as the Trisomy X (47, XXX) Normal sexual development and fertility Tall stature, long limbs, large hands/feet Low muscle tone/muscle weakness (Hypotonia) Very curved pinky finger (Clinodactyly) Widely spaced eyes (Hypertelorism) 2) Jacob’s Syndrome Normal sexual development and sperm production (47, XYY) Tall stature, long limbs, large hands/feet Low muscle tone/muscle weakness Low muscle tone/muscle weakness (Hypotonia) Very curved pinky finger (Clinodactyly) Widely spaced eyes (Hypertelorism) 3) Down Syndrome Referred to as Trisomy 21 (Trisomy at #21) Short stature and shorter neck Almond-shaped eyes with an upward slant Low muscle tone/muscle weakness (Hypotonia) Males are reported to be infertile Females are fertile but with a higher risk of complications during pregnancy 4) Patau Syndrome Referred to as Trisomy 13 (Trisomy at #13) Presence of cleft lip and palate Low birth weight and poor growth Abnormal skin Small head and abnormal eye size Defects found in the heart and internal organs Life-limiting condition, most infants do not survive the first few weeks or months 5) Edwards’ Syndrome Referred to as Trisomy 18 (Trisomy at #18) Presence of cleft lip and palate Abnormally shaped or small head Smaller than average body size Clenched fists with overlapping fingers Small jaw and mouth Low-set ears Defects found in the heart and internal organs Life-limiting condition, most infants do not survive within days to weeks after birth Procedure to Generate a Karyotype 1) Isolate Somatic Cells 2) Stimulate cell division/mitosis using a drug 3) Arrest cells during metaphase for a clearer observation 4) Stain the chromosomes to enhance visibility under the microscope 5) Take an image of the chromosomes for digital analysis and comparison  LG 8.0 - Sexual Life Cycles and Meiosis Lesson 8.1 Cell Division: Meiosis 1) MEIOSIS: Produces FOUR HAPLOID (n) daughter cells from one diploid (2n) parent cell Gamete production is CRUCIAL for SEXUAL REPRODUCTION. It is also called a REDUCTIONAL DIVISION as it results in halving of the normal chromosome number. 2) PHASES of MEIOSIS: MEIOSIS 1 (Reduction Division) ❖ PROPHASE 1: LONGEST PHASE, divided into FIVE SUBSTAGES. - Leptotene: During this stage, chromosomes start to become visible and chromosomal ends converge towards the centrosome. - Zygotene: Homologous chromosomes are joined together in a process called synapsis. Sister chromatids are closely joined together by the synaptonemal complex in this stage. - Pachytene: The chromosomes or bivalents consisting of four chromatids are formed. There is an exchange or a random mixture of genetic material between homologous chromosomes, called crossing-over. This crossing-over of genes contributes to genetic variability and diversity of organisms. - Diplotene: Homologous chromosomes are pulled apart where a distinct split is visible between them, the split is called chiasma (chiasmata) where crossing-over occurred. The chiasmata appear to move toward the end in the process known as terminalization. - Diakinesis: Further chromosomal condensation and nuclear membrane breakdown occur.  ❖ METAPHASE 1: Homologous chromosomes align at the equatorial plate. ❖ ANAPHASE 1: Homologous chromosomes are pulled to opposite poles. ❖ TELOPHASE 1: Two haploid daughter cells are formed. MEIOSIS 2 (Equatorial Division): - Similar to mitosis but without DNA replication. - Results in four haploid cells, each with half the chromosomes of the original cell.  3) GENETIC VARIATION: Crossing-over during prophase I enhances genetic diversity by allowing the exchange of genetic material between chromatids. Recombinant chromosomes result from crossing-over, producing gametes with combinations of genes different from those of the parent. COMPARISON OF MITOSIS AND MEIOSIS Mitosis Meiosis I Meiosis II Occurs in somatic cells germ line cells germ line cells Otherwise known as somatic division reductional division equational division Start 2n 2n n End 2n n n Crossing-Over does not occur occurs in prophase I does not occur Function growth and repair sexual reproduction (with genetic variability) Lesson 8.2 Gametogenesis 1) GAMETOGENESIS: Production of gametes Process of producing haploid (n) cells from diploid (2n) cells through meiosis In Males: Spermatogenesis In Females: Oogenesis Both Spermatogenesis and Oogenesis processes involve meiotic divisions to produce gametes with half the number of chromosomes as each parent A. SPERMATOGENESIS (in males) : ○ It is the process by which mature spermatozoa are formed in males. ○ Leads to the formation of four sperm cells from each primary spermatocyte. ○ Occurs in seminiferous tubules of the testes and starts at puberty.  PROCESS OF SPERMATOGENESIS: 1. Spermatogonia (diploid stem cells) undergo mitosis to produce more stem cells before puberty. 2. At puberty, follicle-stimulating hormone (FSH) stimulates spermatogonia division. 3. One daughter cell (Type A) remains a stem cell, while the other (Type B) becomes a primary spermatocyte. 4. The primary spermatocyte undergoes meiosis I to produce two equal-sized secondary spermatocytes (haploid). 5. Each secondary spermatocyte undergoes meiosis II to produce two spermatids (haploid), resulting in a total of four spermatids from one primary spermatocyte. 6. Spermatids undergo spermiogenesis. - A maturation process where they lose most of their cytoplasm and develop distinct regions: the head (containing the nucleus and acrosome*), the midpiece (containing mitochondria for energy), and the tail (flagellum for motility) *Acrosome - contains enzymes that enable the sperm to digest the membranous barriers that surround the egg The entire process of spermatogenesis takes approximately 64 to 72 days in humans. B. OOGENESIS (in females): ○ The process of producing a mature egg (ovum) in females. ○ Occurs in the ovary’s outermost layer  PROCESS OF OOGENESIS: 1. Primordial germ cells (diploid) migrate to the ovaries during embryonic development. Many of these cells undergo atresia, a process of cell death. 2. Once in the ovaries, the primordial germ cells are called oogonia. - The ovary of a newborn female contains only a few thousand oogonia. 3. Oogonia enter prophase I of meiosis and are then called primary oocytes. The primary oocyte grows for several weeks. 4. When cytokinesis I occurs following telophase I, two daughter cells of highly asymmetric size are formed. - The larger cell is designated as a secondary oocyte, receiving almost all the cytoplasm, and the smaller cell becomes the first polar body. 5. The secondary oocyte is released at ovulation. 6. The rapid completion of the second meiotic division takes place if the secondary oocyte is fertilised by a sperm cell, producing the second polar body plus the egg, sometimes called an ootid. 7. The polar bodies will soon degenerate, playing no further role in development. COMPARISON OF SPERMATOGENESIS AND OOGENESIS Spermatogenesis Oogenesis Start 2n 2n End n n Product 4 spermatids 1 ootid Meiosis I a testis produces new primary an ovary contains all primary spermatocytes oocytes Meiosis II produces sperm cells in an is not completed without a interrupted sequence sperm cell Timing begins at puberty, continuous begins before birth, cyclical throughout life from puberty Cell Size and Division equal division of cytoplasm unequal division of cytoplasm CONSEQUENCES OF MEIOSIS MEIOSIS I (REDUCTIONAL DIVISION) Chromosome pairs are distributed, resulting in daughter nuclei with different genetic contents. Reduces the chromosome number by half. MEIOSIS II (EQUATIONAL DIVISION) Chromosome number remains unchanged. Nuclei resulting from meiosis II are genetically identical except for recombined parts. CONSERVATION OF CHROMOSOME NUMBER Chromosome number remains consistent across generations in sexually reproducing organisms. SEGREGATION OF PAIRED GENES At the end of meiosis, each of the four daughter cells contains one representative of each chromosome pair from the start of meiosis. Provides the physical basis for the segregation of paired genes. CROSSING OVER AND GENETIC VARIABILITY Crossing-over between non-sister chromatids leads to genetic recombination. Results in a virtually infinite number of different gametes. Wide genetic variability is essential for evolution. Enrichment Videos: Introduction to Meiosis ( MEIOSIS - MADE SUPER EASY - ANIMATION ) Spermatogenesis and Oogenesis ( Oogenesis and Spermatogenesis | Reproductive ) Meiosis Square Dance ( Meiosis Square Dance ) TEST YOUR KNOWLEDGE! By: CLARK DE CASTRO , REMELOU JANAIA PIRANTE , & MA. ZOEPHIA VALAQUIO Q2_BiologyPT_PhoTau_Midterm Prepared by Reviewed by Frankie Dumlao KIERRA MARENETH PABALINAS RAFAELLA CONTESSA GERARDO KAIZYLLE JHAECA PRIX JUANITO MA. KRISTIANNE GAYLE MONANA