The process of meiosis

• In meiosis the DNA is replicated, homologous chromosomes are separated and the cell divides (meiosis I, 2n), then each chromosome divides into chromatids which enter four haploid cells which are non-identical to each other and the parent cell (meiosis II, n)
• Process of meiosis:

  Meiosis involves two nuclear divisions that normally occur immediately one after the other

  • Meiosis 1
  • Meiosis 2
• The process of meiosis: First division (meiosis 1)

  • Homologous chromosomes pair up and their chromatids wrap around each other
  • Equivalent portions of these chromatids may be exchanged in a process called crossing over
  • By the end of this division the homologous pairs have separated, with one chromosome from each pair going into one of the two daughter cells
• The process of meiosis: Second division (meiosis 2)

  • The chromatids move apart
  • At the end of meiosis 2, four cells have usually been formed
  • In humans, each of these cells contains 23 chromosomes
• In addition to halving the number of chromosomes, meiosis also produces genetic variation among the offspring, which may lead to adaptations that improve survival chances
• Meiosis brings about genetic variation in two ways:

  • Independent segregation of homologous chromosomes
  • New combinations of maternal and paternal alleles by crossing over