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Meiosis

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).

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Meiosis

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  1. 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.

  2. 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

  3. 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)

  4. 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.

  5. 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.

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