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Biology Main Page
Chapter 6 main
For an organism to reproduce sexually, by definition each parent must contribute some DNA to the new offspring.  The problem is that the cells produced by the body, are diploid.  If the cells were just handed down without reducing the number of chromosomes in the cell, the offspring would have too many chromosomes.  To avoid this problem, the gametes produced, must go through a reduction division called meiosis. 

Meiosis is the process by which the number of chromosomes in a cell are reduced to half that of a body cell.  The process of meiosis takes place in gonads (testes and ovaries).  It begins with a single diploid cell and ends with 4 haploid cells.  The organism now is able to produce an offspring as long as a gamete is present from the opposite sex. 

Meiosis is an orderly process just as mitosis is.  It ensures that the correct number and type of chromosomes are present to contribute to a new offspring.  In fact, meiosis is like mitosis in several ways.  Meiosis starts off with diploid cells, it uses the same steps as mitosis and its' function is to separate chromosomes.  It differs though from mitosis in as many ways.  Meiosis ends up with 4 haploid cells, where as mitosis ends up with two diploid cells.  Meiosis occurs in gonads where mitosis occurs in body cells.

Meiosis prepares to produce gametes by taking chromosomes and splitting up the similar chromosomes and placing them into different cells.  Homologous chromosomes line up in prophase I and are split apart in anaphase I.  Meiosis goes through the four phases of mitosis twice.  By the end of meiosis, 4 haploid cells are produced.