4.2: Meiosis
Two Key features of meiosis contribute to genetic variation:
1. Pairing of homologous chromosomes allows for crossing over, resulting in the
exchange of chromosome sections between non-sister chromatids.
2. Independent assortment of homologous maternal and paternal chromosomes
during metaphase I results in gametes that have different combinations of parental
chromosomes.
Gamete Formation in Animals
Spermatogenesis:
a) Spermatogenesis from spermatogonium cells in the testes starts at puberty.
b) Meiotic divisions are equal. Leading to four spermatozoa from the original
Spermatogonia cell.
c) Meiosis II is completed before the sperm are released from the testes.
Oogenesis:
a) All potential gametes are produced before birth in ovaries as am Oogonium
completes prophase I.
b) Meiotic divisions of the primary oocytes are unequal, resulting the formation of
one large secondary oocytes and smaller polar bodies (eventually destroyed)
c) Puberty release the “arrested state” of secondary oocytes, leading to ovulation.
d) Meiosis II is not completed until fertilization of the secondary oocytes by sperm.