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Meiosis Overview

fertilization - aka syngamy; fuses gametes to form a new cell 

  • gametes - eggs, sperm
  • somatic cells - nonreproductive cells
    • has twice as many chromosomes as gametes
    • never form gametes
  • zygote - formed by 2 gametes fusing together
  • meiosis produces cells w/ 1/2 the normal number of chromosomes
  • sexual reproduction - uses meiosis/fertilization to give chromosomes from 2 parents to offspring
    • 23 maternal homologues from mother, 23 paternal homologues from father in humans
    • life cycles of organisms w/ sexual reproduction alternate between diploid/haploid periods
  • germ-line cells - will eventually produce gametes
    • undergoes meiosis, not mitosis

synapsis - close association of chromosomes during prophase I of meiosis 

  • synaptonemal complex - homologues paired closely along a protein lattice between them
  • pairs of homologues come together during metaphase I
  • homologues, not sister chromatids, go towards opposite poles during anaphase I
  • meiosis I - aka “reduction division”
  • crossing over - genetic recombination
    • homologues can exchange chromosomal information
    • chiasmata - sites of crossing over, maintained until anaphase I
  • continued association of chromosome pairs until anaphase is needed to ensure accurate separation

2 divisions - genetic material only replicated once 

  • produces cells w/ 1/2 the number of chromosomes
  • meiosis II - like mitosis, but without chromosome duplication
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