Meiosis First nuclear division –46 X’s split into 2 nuclei with 23 X’s (one of each kind of chromosome) Second nuclear division –23 X’s split into 2 nuclei with 23 single copy chromosomes Cytokinesis follows both divisions, but interphase only follows second division.

Meiosis (Prophase I) Process: synapsis Two pairs of homologous = tetrad Trading chromosome pieces is crossing over. The X formed by “legs” of the chromsomes overlapping is called a chiasma

Where Mitosis: Any cell not in G0 phase, except in the gonads (ovaries and testes) Meiosis: In the gonads, the germ cells give rise to the gametes (egg and sperm)

When Mitosis: throughout life in some cells, but cell division stops in nerve cells and muscle cells early in life (2-3 years old). Meiosis: –Females: Begins before two years old, then starts again during puberty with one egg made each month. Menopause is when eggs are no longer formed. –Males: Happens throughout life from puberty to death.

Result Mitosis: 2 Diploid cells with 46 single copy chromosomes. Meiosis: 4 haploid cells with 23 single copy chromosomes (one of each kind) –Males: All four are viable cells (sperm) –Females: Of the four cells created, only one will become an egg and the other three becoming polar bodies with little cytoplasm, yet having the full 23 chromosomes.