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Meiosis

meiosis - aka "reduction division"

  • makes haploid daughter nuclei
  • diploid - chromosomes coming in pairs (normal in eukaryotic nuclei)
  • homologous chromosomes - chromosomes in a pair
    • loci - sites for a gene, same in both homologous chromosomes
  • haploid - only 1 chromosome in each pair found (normal in gametes)
  • 2 rounds of chromosomal separation, 1 round of DNA replication
  • synapsis - pairing of homologous chromosomes
    • alleles - homologous segments of genetic material, gets exchanged when chromosomes paired up
    • crossing-over - creates new genetic combination
    • no gain/loss of genetic material
  • meiosis I - homologous chromosomes split
  • meiosis II - chromatids split

gametogenesis - formation of gametes

  • gamete - reproductive cells w/ haploid nuclei
  • spermatogenesis - formation of sperm
    • occurs in testes (made of seminiferous tubules)
    • spermatogonia - diploid cells in tubules that constantly divide mitotically
    • primary spermatocytes - cells that move toward lumen and start meiosis
    • secondary spermatocytes - produced by meiosis I of primary spermatocyte, has haploid set of double-stranded chromosomes
    • spermatids - produced by meiosis II of secondary spermatocytes, matures into sperm cells
  • oogenesis - formation of egg
    • occurs in ovaries of females
    • oocyte - cells in ovary that produces female gametes
    • eggs not produced continually, only during early fetal development
    • primary oocytes - about 2 million initially created, start meiosis I but stop in prophase I
    • follicular cells - surround oocytes to form follicules
    • hormones stimulate growth of 1 or 2 follicles per month after puberty
    • ovulation - release of oocyte from ovary, after oocyte completes meiosis I to produce secondary oocyte and polar body (eventually disintegrates)
    • Graafian follicle - mature follicle containing secondary oocyte
    • meiosis II (only after sperm penetrates egg) creates polar body and haploid egg cell ready for fertilization (nuclei fusion)
    • corpus luteum - formed by remaining follicle cells, prepares the uterus for fertilized egg w/ hormones

plant gametogenesis - plants have alternation of generations between haploid/diploid  

  • meiosis occurs in anthers/ovary of flowers
  • anther creates spores (pollen) that eventually produce male gametes
  • ovary creates spores (ovule) that eventually produce female gametes
Subject: 
Biology
Subject X2: 
Biology

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