Human Genetics and Chromosome Disorders

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Questions and Answers

What is the diploid number of chromosomes in humans?

46 (correct)

Which type of stem cells can differentiate into any other cell type?

Unipotent

Multipotent

Pluripotent

Totipotent (correct)

What is the primary function of karyotyping?

To analyze protein synthesis

To check DNA replication errors

To determine genetic mutations

To examine the number and structure of chromosomes (correct)

During which phase of cell division do homologous chromosomes align in pairs?

Prophase I Signup and view all the answers

What occurs at the chiasma during meiosis?

Interchange of chromatid segments takes place Signup and view all the answers

Which type of stem cells can produce cells of only a single lineage?

Unipotent Signup and view all the answers

What characterizes the structure of DNA?

Double-stranded with deoxyribonucleotides Signup and view all the answers

How many chromosomes are present in the haploid number in humans?

23 Signup and view all the answers

What is the only monosomy compatible with life?

45, X karyotype Signup and view all the answers

Which condition is characterized by the absence of ovaries and short stature in females?

Turner syndrome Signup and view all the answers

What is cri-du-chat syndrome caused by?

Partial deletion of chromosome 5 Signup and view all the answers

Angelman syndrome results from a microdeletion on which chromosome?

Chromosome 15 Signup and view all the answers

What occurs when a gamete with 23 chromosomes fuses with a gamete with 24 chromosomes?

The result is an individual with 47 chromosomes. Signup and view all the answers

Which syndrome is characterized by features such as mental retardation and a catlike cry?

Cri-du-chat syndrome Signup and view all the answers

What condition results from nondisjunction during meiosis?

An extra sex chromosome Signup and view all the answers

What is a common cause of structural chromosome abnormalities?

Environmental factors Signup and view all the answers

Which syndrome results from a defect inherited on the paternal chromosome?

Prader-Willi syndrome Signup and view all the answers

Which of the following features is associated with Down syndrome?

Congenital heart defects Signup and view all the answers

What is a characteristic feature of Klinefelter syndrome?

Presence of a Barr body Signup and view all the answers

Which of the following is true regarding Fragile X syndrome?

Males are affected more often than females Signup and view all the answers

What results from unbalanced translocation?

Loss of essential genetic material Signup and view all the answers

What is the incidence rate of Down syndrome for women under age 25?

1 in 2000 Signup and view all the answers

What is a feature observed in Trisomy 18 (Edwards syndrome)?

Flexion of fingers and hands Signup and view all the answers

What is the primary cause of Trisomy 13 (Patau syndrome)?

An extra copy of chromosome 13 Signup and view all the answers

What process enhances genetic variability during meiosis?

Crossover of genetic material Signup and view all the answers

How many chromosomes does each haploid germ cell contain after meiosis?

23 chromosomes Signup and view all the answers

What happens to the three polar bodies produced during oocyte formation?

They are eliminated and degenerate Signup and view all the answers

What is Turner syndrome associated with in terms of chromosomal abnormalities?

45,X Signup and view all the answers

What chromosome number is indicative of a normal human somatic cell?

46 Signup and view all the answers

What do the terms 'euploid' and 'aneuploid' refer to in genetics?

Chromosome number classifications Signup and view all the answers

What classification is given to a gamete containing 24 chromosomes resulting from nondisjunction?

Aneuploid Signup and view all the answers

How many homologous pairs of chromosomes do humans have in somatic cells?

23 pairs Signup and view all the answers

During which week do germ cells migrate from the yolk sac to the gonads?

Fourth week Signup and view all the answers

What process allows primordial germ cells (PGCs) to increase their cell number?

Mitosis Signup and view all the answers

What happens to PGCs that fail to migrate correctly?

They undergo apoptosis Signup and view all the answers

What is the primary function of PGC migration?

To reach the gonads for gamete formation. Signup and view all the answers

What is the term for the process by which a particular cell develops into its final cell type?

Differentiation Signup and view all the answers

How do PGCs respond when they encounter migration cues?

They move actively towards the gonads. Signup and view all the answers

What is the significance of the negative selection process in PGCs?

To ensure only competent PGCs survive. Signup and view all the answers

Which of the following best describes the initial movement of PGCs during migration?

Initially passive, then active Signup and view all the answers

Which event occurs at the end of prophase during cell division?

The nuclear envelope is broken Signup and view all the answers

What is the role of the kinetochore during metaphase?

To control the entry into anaphase Signup and view all the answers

Which of the following best describes what happens during anaphase?

Sister chromatids split at the centromere Signup and view all the answers

What significant change occurs during telophase?

The nuclear envelope reassembles Signup and view all the answers

What results from the contraction of microfilaments during cytokinesis?

Formation of the cleavage furrow Signup and view all the answers

What happens to chromosomes during the process of telophase?

They revert to a less condensed state Signup and view all the answers

What prevents daughter cells from having unequal numbers of chromosomes?

Metaphase checkpoint influence of the kinetochore Signup and view all the answers

In what phase of the cell cycle does the mitotic spindle disaggregate?

Early G1 phase Signup and view all the answers

Study Notes

Course Outline

Primordial germ cells originate and migrate to the sex cells, colonizing presumptive gonads. Growth and differentiation occur.
Development and organization of testes and ovaries are detailed.
Oogenesis involves meiotic changes in oocytes, zona pellucida formation, follicular growth, and pre- and post-ovulatory atresia.
Spermatogenesis describes testis development before and at puberty, seminiferous epithelium, and spermatozoa formation, including spermatogenic cycle rotations.
Cycles, including puberty, oestrous, and menstrual cycles, and ovulation are detailed.
Fertilization, egg and sperm transport, and sperm penetration are described.
Pre-embryonic periods, trophoblast, inner cell mass, fetal membrane differentiation, and cell differentiation are covered.
Implantation, placental formation at birth, and its role in embryo nutrition and protection are detailed.
Embryogenesis details embryonic area differentiation, primary axial structure formation, intra-embryonic mesoderm differentiation, and embryonic germ layer derivations.

Embryology (Developmental Anatomy)

Embryology studies prenatal embryo and fetus development.
Structural changes from fertilization to adulthood, including embryology, fetology, and postnatal development are part of this study.
Teratology is a part of embryology and deals with abnormal development; includes birth defects.
Genetic and environmental factors affecting development leading to birth defects are part of teratology.

Cellular and molecular descriptions of human development in the womb.
Development of human gametes (spermatozoa and oocytes)
Stem cells and their progeny of cells and tissues
Birth defects
Assisted reproduction technologies (ART)

Stages of a Human Life

Stages of development from fertilization to death and corresponding ages
Prenatal (280 days) to extrauterine (75 years)
Embryonic period (1-8 weeks), Pre- and post-implantation.
Fetal period (9-38 weeks)
Key milestones like puberty, menopause, and andropause are noted.

Common Terms

Biogenesis: the formation of something.
Agenesis: absence of an organ due to the nonexistence of its primordium in the embryo.
Progeny: offspring or descendants of a person or a cell.
Induction: initiating an embryonic phenomenon.
Inducer: the molecular or cellular element initiating induction
Differentiation: specialized features acquired by cells, tissues, and organs during development.
Dedifferentiation: loss of differentiation and cellular orientation; anaplasia; return to a less specialized state.
Morula: tightly packed cells resembling a mulberry bush, a stage in cleavage.
Embryo: developing human from fertilization to 8 weeks.
Fetus: developing human from week nine to birth.
Primordium: first sign of an organ or body region development
Critical Length (CR) and Crown-Heel Length (CH) : different measurement units used for fetal growth.

Stages of Embryonic Development (1-8 Weeks)

Fertilization: fusion of male and female gametes.
Cleavage: cell division of an embryo.
Blastocyst formation: formation of a cystic structure during early embryonic development.
Implantation: attachment of the embryo to the uterine wall.
Gastrulation: process where the embryo forms three germ layers.
Tube formation: elongation of the embryo's body.

Clinically Oriented Problems

Terms for developing human during its beginning.
Differences between conceptus and abortus.
Sequence of events in puberty.
Puberty differences between males and females.
Embryology and teratology differences,

Differentiation

Development of fertilized egg into a multicellular organism.
Mitosis: cell division creating two genetically identical cells.
Daughter cells specialization contributing to mature tissues like muscle and skin cells.

Cell Cycle

Alternation between mitosis and interphase,
known as Cell cycle.
DNA replication—occurring during interphase.
Two-stage division; mitosis and interphase.
Mitosis further broken down to four stages: prophase, metaphase, anaphase, and telophase. Interphase Go, S, G1, and G2.

Interphase

Resting phase of a cell cycle.
Cell prepares for division, including growth and replication.
Occupies 95% of cell cycle.
Three phases: G1, S, and G2 (each with specifics).
Go phase—quiescent phases for cells like nerve and muscle.

G1 Phase (Presynthesis)

Cell between mitosis and DNA replication initiation.
Metabolically active growth occurs without DNA duplication.
Duration varies based on cell type (e.g., 25 hours in bone tissue).
Restriction point (R): a checkpoint regulates cell cycle entry if favorable conditions present.
Synthesizes RNA and proteins.

Go Phase

Quiescent phase.
Cells (e.g., muscle, nerve) remain in a non-dividing state.
Cells might exit for indefinite times or enter the cell cycle again.

S Phase (Synthesis)

DNA replication during cell cycle - centriole division into two pairs in cells containing centrioles.
Synthesis duration is approximately eight hours.

G2 Phase

Energy accumulation for mitosis and synthesis of tubulin for microtubules formation.
Synthesis of cellular components needed prior to mitoses initiation.
Checkpoint to ensure DNA replication is complete and correct before mitosis.

M Phase (Mitosis)

Complete reorganization into progeny with equal chromosomes as the parent cell.
Cytokinesis: division of cytoplasm to create two daughter cells.
Four overlapping phases: Prophase, metaphase, anaphase, telophase.

Mitosis

Eukaryotic cell division generating similar daughter cells that match the parent cell.
Mitotic spindle: specialized structure with microtubules, pulling chromosomes apart.
Chromosomes duplication occurs before mitosis.

Prophase

Chromosomes become visible, within the nucleus and gradually condense.
Chromosomes shorten and thicken.
Chromatids are linked at centromere.
Centrosomes move to the opposite poles forming microtubules of the mitotic spindle.
Nuclear envelope breaks down.

Metaphase

Chromosomes align at the cell's equator and attach to microtubules forming the mitotic spindle.
Checkpoint ensures all chromatid pairs are properly oriented for division.

Anaphase

Sister chromatids separate at the centromeres and move towards opposite poles of the cell.
Pulling the separate chromatids is along the microtubules.
Mitotic spindle lengthens.
Centrioles also move apart and are drawn to the opposite cell ends.

Telophase

Nuclei reappear in daughter cells.
Chromosomes relax and disperse.
Nuclear envelope forms around chromosomes.
Cytoplasmic division begins with formation of cleavage furrow.
Mitotic spindle breaks down completely.

Chromosome Theory of Inheritance

Humans have approximately 35,000 genes in 46 chromosomes.
Somatic cells have 23 homologous pairs of chromosomes; 22 are autosomes, and 1 is sex chromosome.
XX—female, XY—male
Each gamete contains a haploid number (23 chromosomes).

Numerical Abnormalities

Normal human somatic cells contain 46 chromosomes. Normal gametes contain 23.
Euploid—exact multiples of n; Diploid/Triploid.
Aneuploid—not an exact multiple of n; Trisomy/Monosomy; results from non-disjunction.

Meiosis

Cell division forming gametes (male/female).
Two divisions—Meiosis I and II.
Meiosis I—reducing chromosome number to haploid.
Meiosis II—separating sister chromatids.
Homologous pairs separate resulting in two daughter cells.

Crossover

Critical event in meiosis I.
Interchange of chromatid segments between paired homologous chromosomes.
Segments exchange as homologous chromosomes separate.
Interchange points form temporary connections (chiasma).
Genetic variability enhancement occurs through crossover.

Polar Bodies

Results of meiosis in oocytes and spermatocytes.
Oocyte produces four cells; only one matures; the other three (polar bodies) are without cytoplasm.
Spermatocyte produces four daughter cells; two with XY and two with XX chromosomes.
Oocyte formation contrasts with spermatocyte formation.

Clinical Correlates (Birth Defects and Spontaneous Abortions)

Chromosomal abnormalities (numerical or structural) are causes of birth defects.
Common chromosomal anomalies include 45,X (Turner syndrome), triploidy, and trisomy 16.
7% major birth defects are due to chromosomal abnormalities. Gene mutations can potentially add 8%.

Trisomy 21 (Down Syndrome)

Caused by an extra copy of chromosome 21 (meiotic non disjunction, mostly oocyte formation).
Features include growth retardation, varied mental retardation, cranial facial abnormalities, facial features, small ears, cardiac defects, and hypotonia.
Incidence is approximately 1 in 2000 (under 25 yrs), 1 in 300 (age 35) and 1 in 100 (age 40).

Trisomy 18 and 13

Trisomy 18 (Edward syndrome) and trisomy 13 (Patau syndrome), caused by chromosomal errors; characterized by diverse physical and intellectual disabilities affecting various body systems and organs.

Klinefelter syndrome

Primarily in males.
Diagnosed during puberty.
Sterility, testicular atrophy, seminiferous tubules hyalinization.
Usually accompanied by gynecomastia.
Sex chromosomal abnormalities (XXY or XXXY types; with presence of Barr bodies).
Incidence is approximately 1 in 500 males
Nondisjunction of the XX homologous pair is common.

Turner Syndrome

Female monosomy (45,X karyotype), compatible with life.
Absence of ovaries (gonadal dysgenesis), short stature, webbed neck, edema.
80% cases are due to male gamete non disjunction.
Remainder are from structural X chromosome defects.

Triple X syndrome

Female (XXX karyotype), often with mild features; often has no visible symptoms, though potentially impacting neurobehavioral development and physical characteristics.

Structural Chromosome abnormalities

Involve one or more chromosome breakage, usually due to environmental factors (viruses and radiation).
Partial deletion can cause various syndromes.
Cri-du-chat syndrome (chromosome 5); well-known, characterized by distinct features like cat-like cry, microcephaly, mental retardation, and congenital heart disease, resulting from partial deletion on the short arm of chromosome 5.

Microdeletions

Microdeletion syndromes or contiguous gene syndromes arise due to missing gene segments.
Angelman syndrome (maternal chromosome 15 deletion) and Prader-Willi syndrome (paternal chromosome 15 deletion).
These conditions impact development, involving diverse symptoms and degrees.

Fragile X Syndrome

Fragile sites on chromosomes, showing high propensity to break during cell manipulation.
Fragile X syndrome is caused by an alteration in the X chromosome (primarily on the long arm).
Characterized by mental retardation, large ears, prominent jaw, and pale blue irides are some symptoms.
Males are often more commonly affected than females.

Gene Mutations

Birth defects caused by changes in single gene structure or function.
Genes exist as allele pairs, one from each parent.
Dominant mutation: abnormality caused by a single mutant gene copy.
Recessive mutation: abnormality caused by both allele copies mutated.

Diagnostic Techniques for Identifying Genetic Abnormalities

Cytogenetic analysis
High-resolution metaphase banding techniques
Fluorescence in situ hybridization (FISH)
Spectral karyotype analysis

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Description

This quiz explores key concepts in human genetics, including chromosome numbers, types of stem cells, karyotyping, and various genetic disorders. Test your knowledge on the characteristics of DNA, meiosis, and the implications of chromosomal abnormalities. Ideal for students studying genetics or related fields.