Cards (12)

  • meiosis = sexual reproduction, produces gametes, gentetically different
    1. prophase 1
    • homologous chromosomes pair up (bivalent)
    • bivalent condenses and the chromosomes join at several points (chiasma)
    • some genetic material is exchanged (crossing over)
    • centrioles start to form the spindle and the nuclear membrane begins to break down
  • 2. metaphase 1:
    • bivalents arrange themselves along the equator
    • independent assortment of chromosomes creates variation
  • 3. anaphase 1:
    • the centromeres do not divide - both chromatids are pulled towards opposite poles by the spindle fibres
    • chromosomes separated into 2 haploid sets of chromosomes in the daughter cells
    • independent assortment creates variation
  • 4. telophase 1:
    • homologous chromosomes are now at opposite ends of the cell
    • chromosome number has been halved
    • each chromatid is genetically different
    • nuclear membrane begins to reform and cell splits
  • 5. prophase 2:
    • nuclear membrane breaks down
    • chromatids shorten and thicken
    • centrioles move to opposite poles and form the spindle - often at right angle to the first ones
  • 6. metaphase 2:
    • chromatids arrange themselves along the equator
  • 7. anaphase 2:
    • centromeres divide and spindle fibres pull to opposite poles - chromatids now called chromosomes
    • independent assortment of the chromatids creates genetic variation
  • 8. telophase 2:
    • chromosomes uncoil and lengthen
    • spindle disappears and nuclear membrane reforms
    • each nucleus now has half the number of chromosomes (haploid)
  • spermatogenesis = making of sperm cells
  • oogenesis = making of egg cells (ovum)
  • gametogenesis = formation of gametes (sex cells)