Gametogenesis (normal development):
- Describe the five stages of cell division
- Describe the four stages of mitosis
- List two ways in which meiosis contributes to genetic diversity and why it is considered beneficial
- Identify a normal male and female karyotype and enumerate the number of chromosomes, autosomes, DNA content and ploidy. Interpret the short-hand notation of karyotype
- Describe the major stages of meiosis and the status of the chromosomes, DNA content and ploidy at each
- Define the terms chiasmata, crossing over, translocation, disjunction and non-disjunction and identify the phase of meiosis at which each may occur.
- Identify the origin and migratory path of human germ cells into the gonad. Describe the role of growth factors and their receptors in this migration.
- Distinguish spermatogenesis and spermatogenesis. When is spermatogenesis initiated, when does it cease? How long does the entire process of spermatogenesis/spermatogenesis take?
- Describe the physical site, timing, cell morphology, stage of meiosis for each stage of spermatogenesis. Relate the stage of sperm development with location within the seminiferous tubule.
- Describe the modification which takes place during spermatogenesis including their function and the anatomical site of modification.
- Describe the physical site, timing, cell morphology and stage of meiosis for each stage of oogenesis. What are the major triggers for moving the developing oocyte from one stage to the next?
- Describe the origin, hormonal control, and roles of accessory cells in male and female gametogenesis.
Full Answer Section
- Telophase: During telophase, the nuclear envelope reforms and the chromosomes decondense.
Four stages of mitosis
- Prometaphase: During prometaphase, the microtubules of the mitotic spindle begin to attach to the kinetochores of the chromosomes.
- Metaphase: During metaphase, the chromosomes align in the middle of the cell, forming the metaphase plate.
- Anaphase: During anaphase, the sister chromatids separate and move to opposite poles of the cell.
- Telophase: During telophase, the nuclear envelope reforms and the chromosomes decondense.
Meiosis and genetic diversity
Meiosis contributes to genetic diversity in two ways:
- Crossing over: During crossing over, homologous chromosomes exchange genetic material. This can lead to new combinations of genes in the offspring.
- Independent assortment: During meiosis, the chromosomes are sorted independently of each other. This means that each offspring inherits a unique combination of chromosomes from their parents.
These two processes ensure that each offspring is genetically unique, which increases the chances of the species surviving and adapting to new environmental conditions.
Normal male and female karyotype
The normal male karyotype is 46,XY. This means that males have 46 chromosomes, including 22 pairs of autosomes (chromosomes that are not sex chromosomes) and one pair of sex chromosomes (XY).
The normal female karyotype is 46,XX. This means that females have 46 chromosomes, including 22 pairs of autosomes and one pair of sex chromosomes (XX).
Interpreting the short-hand notation of karyotype
The short-hand notation of karyotype is a way of writing out the chromosomal makeup of an individual. It is typically written as follows:
Number of chromosomes, sex chromosomes, other chromosomes
For example, a normal male karyotype would be written as 46,XY. A normal female karyotype would be written as 46,XX.
Major stages of meiosis
The major stages of meiosis are:
- Prophase I: During prophase I, the homologous chromosomes pair up and crossing over occurs.
- Metaphase I: During metaphase I, the homologous chromosomes align in the middle of the cell, forming the metaphase plate.
- Anaphase I: During anaphase I, the homologous chromosomes separate and move to opposite poles of the cell.
- Telophase I: During telophase I, the nuclear envelope reforms and the chromosomes decondense.
- Prophase II: During prophase II, the nuclear envelope breaks down and the chromosomes condense.
- Metaphase II: During metaphase II, the chromosomes align in the middle of the cell, forming the metaphase plate.
- Anaphase II: During anaphase II, the sister chromatids separate and move to opposite poles of the cell.
- Telophase II: During telophase II, the nuclear envelope reforms and the chromosomes decondense.
Status of the chromosomes, DNA content, and ploidy at each stage of meiosis
Chiasmata, crossing over, translocation, disjunction, and non-disjunction
- Chiasmata: Chiasmata are the visible