Topic 2C: Gametogenesis

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In human males, meiosis results in formation of 4 gametes (sperm)

In human females, meiosis results formation of 4 cells, which combine to form 1 functional oocyte supported by polar bodies

gametes in both males and females are produced in the gonads

Topic 1c: Meiosis and Sex Chromosomes

Sperm are motile and have different parts, while oocytes are round and non-motile, are just 1 large cell.

Ovum and sperm have different contributions to the offspring.

ovum contribute DNA, organelles, epigenetics etc.

sperm contribute only DNA

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Oogenesis: maturation of an egg

begins with a germ cell, oogonium, which undergoes mitosis to increase # of cells to the millions in the embryo

primary oocyte begins meiosis prior to the birth of a female. At birth, there are ~700,000 follicles. At the start of puberty (12-14 yo), the # reduces to 200,000 follicles.

until puberty begins, the follicles remain arrested in prophase I

at adolescence, anterior pituitary gland secretes hormones causing the development of follicles. The oocyte completes meiosis I, resulting in 2 unequal daughter cells

the secondary oocyte is larger and has a greater amount of organelles and material. The smaller cell is the polar body, eventually dies.

they are arrested at metaphase II

Meiosis II will be completed if fertilization happens, to form a mature egg (ovum)

the remaining 2 daughter cells are polar bodies, which are eventually degraded

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Spermatogenesis:

​​​​​​​spermatogonia (diploid cells in the testes) differentiate into primary spermatocytes via mitosis

primary spermatocytes undergo meiosis I producing secondary spermatocytes (haploid)

secondary spermatocytes undergo meiosis II producing 4 spermatids.

The spermatids become spermatozoa (mature sperm) after differentiation.

production of sperm through meiosis

sperm structure:

tail: flagellum propelled by ATP

head: contains the nucleus

acrosome: digestive enzymes used to penetrate the egg

requires testosterone so begins at puberty

testosterone is secreted during development just so male reproductive structures can develop, and then secretion is halted until puberty

4 sperm cells per cycle as men release millions of sperm per fertilization attempt