Gametogenesis and Meiosis

Study Notes

Meiosis does not resume until puberty in males, whereas in females, it begins before reaching sexual maturity and is limited to a certain number of eggs.
In females, the first meiosis occurs before reaching sexual maturity, and the meiotic prophase I is prolonged to accumulate enough building materials for the embryo and to produce large eggs.

Spermatogonia enter meiosis from puberty till death, taking only a few weeks to form spermatozoa.
Spermatogenesis occurs in the seminiferous tubules of the testis, which are the functional units of the testis.
Sertoli cells, which are connective tissue sheaths, surround the seminiferous tubules and play a crucial role in spermatogenesis.
Sertoli cells inhibit spermatogonia proliferation before puberty and provide support for simultaneous gene transcription during prophase I.

Oogonia produce two types of cells: the egg (large gamete) and polar bodies (tiny haploid sister cells).
Oogenesis involves an incomplete meiosis cycle, where meiosis I is completed, but only up to prophase II and metaphase II.
The egg matures at a rate of one per cycle until menopause.
During prophase I, the egg accumulates RNA, yolk, and protein, and during metaphase II, it awaits fertilization.

Sertoli cells are essential for spermatogenesis, but nurse cells are not present in mammals.
Nurse cells are found in some species, where they undergo polypliody (DNA replication without mitosis) and are connected to the oocyte by cytoplasmic bridges.
Nurse cells synthesize and transfer RNA to the oocyte during early oogenesis and transfer massive cytoplasm during late oogenesis.

Yolk formation occurs during prophase I cell arrest, where nutrients are deposited in the oocyte.
The yolk consists of protein, lipid, and glycogen, and its purpose is to provide nutrients for the embryo.