Meiosis Meiosis is a reductive cell division. It involves two divisions to produce four non-identical daughter cells each containing half the number of chromosomes of the parent cell.  Meiosis occurs in all organisms carrying out sexual reproduction. Meiosis reduces the number of chromosomes by half, so that when fertilization occurs, the number of chromosomes would be reestablished. If meiosis did not occur, fusion of gametes would result in a doubling of the chromosomes for each successive sexually reproduced generation. Genetic Variation. Meiosis provides opportunities for new combinations of genes to occur in the gametes. This leads to genetic variation in the offspring produced by random fusion of the gametes.

Comparison with Mitosis   Mitosis  Meiosis No. of divisions A single division resulting in two cells. Two divisions resulting in four cells. Events in Prophase Chromosomes do not associate with each other. No chiasmata formed. Paring of homologous chromosomes.   chiasmata form between non-sister chromatids of homologous chromosomes. Events in metaphase Individual chromosomes are arranged on the equator of the spindle. Pairs of homologous chromosomes are arranged on the equator of the spindle. Events in anaphase Centromere splits and chromatids separate. The chromatids stay joined and the homologous chromosomes separate. Chromosome number in daughter cells Daughter cells have the same number of chromosomes. Daughter cells have half the number of chromosomes. Genetic variation in daughter cells Daughter cells are genetically identical with each cell and with the parent cell. Daughter cells are genetically different with each cell and with the parent cell. Occurrence May occur in all parts of the body. Meiotic division is restricted to the gonads. The process of meiosis consists of two parts, meiosis I and meiosis II. meiosis II is similar to the processes of mitosis, and we will not touch on it. meiosis I, however, has some fundamental differences from Mitosis. These differences occur in prophase and metaphase. We will look into them in the next a few pages.   Relating Topics - Random Assortment