by Jennifer Vose

Created on: January 13, 2008

Meiosis is the division of cells for the purpose of making gametes, or sex cells. Sex cells are different from somatic, or body cells. Sex cells have half the chromosomes of somatic cells. This halving of chromosomes is achieved through the steps of meiosis.

In normal somatic body cells, like a liver cell or a kidney cell, chromosomes are arranged in pairs. You get one copy of your chromosomes from mom, and one copy of the chromosomes from dad. These two copies work together. The genes on each pair of chromosomes match, and the chromosome pairs are known as homologous pairs, meaning that they have the same genetic information in the same location.

Having pairs of chromosomes is known as being diploid. Somatic cells are diploid. Human diploid cells have 23 pairs of chromosomes, or 46 total chromosomes. Gametes, on the other hand, are haploid, a term referring to only having one copy of each chromosome. Human haploid gametes have 23 un-paired chromosomes.

To successfully reproduce, your homologous pairs in somatic cells must be split in half to send to your offspring. Two haploid gametes will unite to make a diploid zygote, the first initial cell of a new individual. The zygote is the fertilized egg cell. Thus, meiosis and the reduction in chromosomes from diploid to haploid becomes necessary for successful reproduction. Having even a single extra copy of a chromosome can be fatal or genetically disabling. For example, an extra copy of the 21st chromosome is the cause of Down Syndrome. An extra copy of the 23 chromosome, the ones that contribute genes for gender determination, can result in disorders like Klinefelter's Syndrome. Successfully reducing chromosomes from pairs to single copies is essential to successful reproduction.

Somatic cells divide through a process called mitosis. Mitosis consists of steps that duplicate the genetic information, condense it into easily sort-able chromosome form, arrange it along the mid-line of a cell, split the duplicated chromosomes in half, and the whole process concludes when the entire parent cell splits in half, resulting in identical daughter cells. Each new daughter cell is a somatic cell with identical copies of genetic material, and the chromosomes are still in pairs.

The cell's life cycle begins with Interphase. Interphase is like the "childhood" stage for a somatic cell. During this time a cell grows, does its job, and begins to ready itself for cell division. By doubling the genetic material, the DNA, the cell ensures

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