39. Gametogenesis. Spermatogenesis. Oogenesis.

Question 1

Gametogenesis

Answer 1

-Process of formation of gametes (sex cells) from spermatogonia and oogonia (immature sex cells)
-In animals and humans, it takes place in specialised organs (gonads)
-Spermatogenesis (formation of sperm) occurs in epithelium of wall of convoluted tubules of testes
-Oogenesis (formation of eggs) takes place in follicles in ovaries under action of follicle-stimulating and luteinizing hormones

Question 2

Similarities between spermatogenesis and oogenesis.

Answer 2

-Start from diploid precursor cells (spermatogonia and oogania)
-These cells, after a period of mitotic division, enter meiosis, becoming haploid cells.

Question 3

Differences between spermatogenesis and oogenesis

Answer 3

Oogenesis:

-Growth: Oocytes grow large, surrounded by a follicle.
-Meiosis: Begins embryonically, stops twice (prophase I, metaphase II), ends at fertilization.
-Accumulation: Ribosomes, yolk, glycogen, lipids, mRNA.
-Function: From puberty to menopause.

Spermatogenesis:
-Reduction: Spermatocytes shrink post-meiosis.
-Structures:
–Compacted nucleus.
–Acrosome (attaches to egg).
–Tail (axoneme) with mitochondria.
-Meiosis: Begins at puberty, continuous until old age.

Question 4

Spermatogenesis

Answer 4

Process: Starts at puberty, continuous until old age.

Location: Epithelium of testicular tubules (~300 m in length).

Spermatogonia Types:
-Type Ad: Dark, stem cells, produce type Ap.
-Type Ap: Pale, produce type B.
-Type B: Round nuclei, produce primary spermatocytes.

Primary Spermatocytes:
Diploid (46 chromosomes), undergo meiosis I to form secondary spermatocytes.

Secondary Spermatocytes:
Haploid (23 chromosomes), undergo meiosis II to form spermatids.

Spermatids:
Result: 4 haploid spermatids from 1 spermatogonium.

Spermiogenesis:
Formation of mature sperm structures: condensed nucleus, acrosome, axoneme, and mitochondria.

Question 5

Oogenesis

Answer 5

1.Primordial Cells: Migrate to gonads, become oogonia.

2.Proliferation: Oogonia divide by mitosis until 11-12 weeks of embryo development.

3.Primary Oocytes: Enter meiosis I, stop at diplotene of prophase I until puberty.

4.Ooplasmic Segregation: Continues despite meiosis pause.

5.Oocyte Maturation: Begins at puberty, hormone-stimulated.
-Telophase I: Asymmetric cytoplasm division forms large secondary oocyte and small polar body.
-Meiosis II: Starts, stops at metaphase II before ovulation.
-Follicle Maturation: Most die; ~400-450 mature out of ~400,000.
6. Ovulation: Mature egg leaves ovary, completes meiosis II if fertilized.