BIOL239 Lecture Notes - Lecture 6: Egg Cell, High Tech, Gametogenesis
25 Mar 2018
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Somatic cells: mitotically dividing and g-arrested cells, (cid:373)ake up vast (cid:373)ajorit(cid:455) of i(cid:374)dividual"s tissues, diploid in humans (2n) Germ cells: pockets of specialize cells (2n for humans, produce gametes (egg/sperm, undergo meiosis, gametes are haploid (n; one of each chromosome) in humans incorporated into ovaries and testis. An overview: germ cells undergo two successive nuclear divisions to produce gametes, meiosis i: separation of chromosome pairs 2n n, meiosis ii: separation of sister chromatids. Prophase i: leptotene looks like mitosis prophase: chromosomes duplicated and condense, centrosomes begin to move to each pole and produce spindle fibres. Prophase i: zygotene*: chromosomes are maximally condensed prior to synapsis, condensed chromosomes seek out homologous partner, synaptonemal complex forms (elaborate protein structure, homologous chromosomes form tetrads (bivalents joined) Prophase i: diakinesis: chromatids thicken and shorten the nuclear membrane breaks down and the spindle begins to attach to kinetochore, non-sister chromatids that have exchanged parts by crossing-over remain closely associated at the chiasmata.
