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.