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Questions and Answers
What occurs during synapsis in meiosis I?
What occurs during synapsis in meiosis I?
- Crossover segments are exchanged.
- DNA replication takes place.
- Sister chromatids separate.
- Homologous chromosomes pair up. (correct)
What structure is formed by the pairing of homologous chromosomes?
What structure is formed by the pairing of homologous chromosomes?
- Sister chromatid
- Chiasma (correct)
- Chromatid
- Centromere
What is the role of crossover during meiosis I?
What is the role of crossover during meiosis I?
- It replicates centromeres.
- It prevents chromatid separation.
- It increases genetic variability. (correct)
- It creates identical daughter cells.
During which phase do homologous chromosomes separate?
During which phase do homologous chromosomes separate?
How many secondary spermatocytes are produced after meiosis I in males?
How many secondary spermatocytes are produced after meiosis I in males?
What occurs during meiosis II?
What occurs during meiosis II?
What is true about DNA replication in meiosis II?
What is true about DNA replication in meiosis II?
How many crossovers typically occur during each meiotic I division?
How many crossovers typically occur during each meiotic I division?
What is gastrulation primarily involved in?
What is gastrulation primarily involved in?
What defines a diploid cell in humans?
What defines a diploid cell in humans?
What occurs during the formation of the tube-within-a-tube body plan?
What occurs during the formation of the tube-within-a-tube body plan?
How many genes are approximately found on human chromosomes?
How many genes are approximately found on human chromosomes?
What characterizes linked genes?
What characterizes linked genes?
Which condition is an example of aneuploidy?
Which condition is an example of aneuploidy?
What is NOT a characteristic of euploid cells?
What is NOT a characteristic of euploid cells?
What does 'C value' refer to in genetics?
What does 'C value' refer to in genetics?
What is the primary stage at which most primary oocytes remain arrested before puberty?
What is the primary stage at which most primary oocytes remain arrested before puberty?
At what stage of prenatal development does the total number of germ cells in the ovary reach its maximum?
At what stage of prenatal development does the total number of germ cells in the ovary reach its maximum?
During which phase do most oocytes become atretic during childhood?
During which phase do most oocytes become atretic during childhood?
What is the estimated range of primary oocytes present at birth?
What is the estimated range of primary oocytes present at birth?
What defines a primordial follicle?
What defines a primordial follicle?
What initiates the process of cell death among oogonia and primary oocytes?
What initiates the process of cell death among oogonia and primary oocytes?
How long can some dormant oocytes remain in the diplotene stage before ovulation?
How long can some dormant oocytes remain in the diplotene stage before ovulation?
Which type of cells surround the clusters of oogonia during development?
Which type of cells surround the clusters of oogonia during development?
What is the purpose of mitosis?
What is the purpose of mitosis?
At which stage of mitosis do chromosomes first become distinguishable?
At which stage of mitosis do chromosomes first become distinguishable?
How many chromosomal sets are present in diploid cells before cell division?
How many chromosomal sets are present in diploid cells before cell division?
What is the main outcome of meiosis?
What is the main outcome of meiosis?
During which phase do the chromatids migrate to opposite poles of the spindle?
During which phase do the chromatids migrate to opposite poles of the spindle?
What restores the chromosome structure after mitosis concludes?
What restores the chromosome structure after mitosis concludes?
What initiates the formation of the mitotic spindle?
What initiates the formation of the mitotic spindle?
What differentiates haploid cells from diploid cells?
What differentiates haploid cells from diploid cells?
What is the primary focus of embryology?
What is the primary focus of embryology?
Why is studying embryology important for physicians?
Why is studying embryology important for physicians?
What percentages of live-born children are likely to have significant malformations?
What percentages of live-born children are likely to have significant malformations?
What are the two main periods of human embryology?
What are the two main periods of human embryology?
What process describes the conversion of germ cells into gametes?
What process describes the conversion of germ cells into gametes?
What is the primary event that follows fertilization?
What is the primary event that follows fertilization?
What characterizes the embryonic period of human development?
What characterizes the embryonic period of human development?
Which of the following is NOT a phase of human embryology?
Which of the following is NOT a phase of human embryology?
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Study Notes
Introduction to Medical Embryology
- Embryology studies developmental events before birth.
- Understanding embryology is crucial due to the incidence of birth defects (3-4% of live-born children).
- Knowledge aids in comprehending adult anatomy and connections between basic and clinical sciences.
Periods and Phases of Human Embryology
- Embryonic Period: First 8 weeks post-fertilization marked by rapid changes.
- Fetal Period: From the 9th week to birth; characterized by fetal growth and organ maturation.
- Key Phases:
- Gametogenesis: Formation of male (sperm) and female (egg) gametes.
- Fertilization: Fusion of gametes to form the zygote.
- Cleavage: Rapid cell divisions post-fertilization.
- Gastrulation: Formation of three primary germ layers (ecto-, meso-, endoderm) and body axes.
- Organogenesis: Development of organs and organ systems.
Chromosome and Gene Basics
- Humans possess approximately 23,000 genes across 46 chromosomes (23 pairs).
- Chromosomes include 22 pairs of autosomes and one pair of sex chromosomes (XX = female, XY = male).
- Ploidy indicates the number of chromosome sets: somatic cells (diploid, 2N) have 46 chromosomes, while gametes (haploid, 1N) have 23.
Mitosis
- Mitosis divides one cell into two genetically identical daughter cells, preserving the chromosome number.
- Phases include:
- Prophase: Chromosomes condense & become visible; each chromosome has two chromatids.
- Metaphase: Chromosomes align at the equatorial plane, connected by microtubules.
- Anaphase: Chromatids separate and move to opposite poles.
- Telophase: Chromosomes de-condense, nuclear envelope reforms, and cytokinesis occurs.
Meiosis
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Meiosis produces gametes through two divisions: Meiosis I and Meiosis II, reducing chromosome number to haploid (23).
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Meiosis I:
- Homologous chromosomes undergo DNA replication, then align in pairs (synapsis).
- Chiasma formation allows for genetic recombination (crossovers), enhancing genetic diversity.
- Results in two daughter cells that are secondary spermatocytes in males and a secondary oocyte with a first polar body in females.
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Meiosis II:
- Sister chromatids are separated without prior DNA replication.
- Final stages result in four haploid gametes from one original germ cell.
Oogenesis
- Oogonia proliferate by mitosis, with a maximum of about 7 million germ cells by the fifth month of prenatal development.
- Most oogonia degenerate by the seventh month; surviving primary oocytes enter prophase of meiosis I and remain arrested until puberty.
- At birth, 700,000 to 2 million primary oocytes are present, with approximately 400,000 by puberty; fewer than 500 are ovulated during reproductive years.
Conclusion
- Understanding gametogenesis, embryology phases, and cell division processes is fundamental for medical studies and practices, aiding in addressing reproduction-related clinical issues.
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