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CHAPTER 22: THE REPRODUCTIVE SYSTEMS

III.Meiosis (continued)

F. The (Specific) Stages of Meiosis:  See Fig 22.6, page 886 and Fig 22.8, page 887.

1.Introduction:

Meiosis is similar to mitosis in that the chromosomes (DNA) are duplicated prior to the process, however this single replication is followed by two consecutive cell divisions called Meiosis I and Meiosis II.

2. Interphase I:

a.Chromosomes replicate in parent cell;

b.23 pairs of duplicated chromosomes.

3. Meiosis I:See Fig 22.6, page 886

a.reduction division:

b.4 stages:

Prophase I:

1.Chromosomes shorten & thicken;

2.Nuclear envelope/nucleoli disappear;

3.Mitotic spindle appears;

4.Chromosomes form tetrads (synapsis); (i.e Homologous pairs are arranged together).  

See Fig 22.7, page 886.

Metaphase I:

1.Homologous chromosome pairs line up along metaphase plate.

Anaphase I:

1.Homologous pairs separate;

2.One member of each pair moves to opposite pole;

3.Cleavage furrow starts to form.

Telophase I and cytokinesis:

1.Cleavage furrow complete;

2.2 daughter cells containing half the chromosome number of parent cell (23 duplicated chromosomes).

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