Phases of Meiosis

Human Physiology

Lesson 06 : Meiosis

Phases of Meiosis

Human reproduce sexually by the fusion of an egg and a sperm. Like almost every cell in our body, this new cell a zygote, has a full contingent of 23 pairs of chromosomes. But what about its parent cells, the sperm and egg? If the egg and sperm each had 23 chromosome pairs, their union would result in a zygote with 46 pairs, double the usual number. Theoretically, this cell would then grow into a person with 46 pairs of chromosomes per cell (rather than the usual 23 pairs). Subsequent generations would have even more chromosomes per cell. But this does not actually happen. To accomplish that task, a special kind of cell division called meiosis takes place. In preparation for meiosis, the chromosomes are copied once, just as for mitosis, but instead of one cell division, there are two. The result is four daughter cells, each containing 23 individual chromosomes rather than 23 pairs. Meiosis occurs in germ cells, which are destined to form gametes in sexually reproducing organisms.

Essential event that takes place in meiosis are;

  • Two successive divisions without any DNA replication occurring between them.
  • Paring and formation of chiasmata and crossing over.
  • Segregation of homologous chromosomes and
  • Separation of sister chromatids.
Last modified: Tuesday, 10 April 2012, 5:33 AM