MEIOSIS (the creation of sex cells) Meiosis is very similar to mitosis. The main difference is that the cell goes through TWO divisions instead of just one. So the result is not two identical diploid cells, but four cells having only one member of each chromosome pair (haploid). Look at the pictures below that point out the differences from mitosis. A cell that is going to go throuhg meiosis in the testes or the ovaries starts off as a “regular” cell. During interphase, the DNA doubles, just as it would for any other cell.

From here on out, the process is different than mitosis

Prophase I: Chromatid pairs form a TETRAD (a group of four). In mitosis, the pairs were separate from one another.

METAPHASE 1:

Through a process called “crossing over”, the chromatids become intertwined with each other and actually exchange pieces with one another.

ANAPHASE 1: The tetrads line up in the cell during metaphase 1 and are pulled apart during anaphase 1. Note that the sections of the chromosomes are not the same as when they came out of interphase (all red or all yellow). The chromatids are still connected by the centromere.

During Telophase / Cytokinesis 1, the cells split, but the cells have two copies of one chromosome pair. Because these are sex cells, they only want one… so……

… they go through a Prophase II, Metaphase II, Anaphase II….

… and finally Cytokinesis II. The result is four cells that have only one member of each homologous pair, or 23 chromosomes.