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Meiosis
The Stages of Meiosis I and Meiosis II
Stage | Description |
---|---|
Prophase I | chromatin condenses and supercoils; chromosomes shorten and thicken; chromosomes join in homologous pairs to form a bivalent; non-sister chromatids attach at chiasmata; crossing over; nucleolus disappears; nuclear envelope disintegrates; spindle forms |
Metaphase I | bivalents arrange themselves on the equator of the spindle, attached to spindle microtubules at the centromeres; the bivalents are randomly arranged |
Anaphase I | homologous chromosomes are pulled by the spindle microtubules to opposite poles; centromeres do not divide; chiasmata separate |
Telophase I | in animal cells, two new nuclear envelopes form and the cell divides by cytokinesis; most plant cells do not have telophase I |
Prophase II | nuclear envelope disintegrates; nucleolus disappears; chromosomes condense; spindles form |
Metaphase II | chromosomes arrange themselves on the equator of the spindle, attached to spindle microtubules at the centromeres; the chromatids are randomly arranged |
Anaphase II | centromeres divide and chromatids are pulled to opposite poles by the spindle fibres; chromatids randomly segregate |
Telophase II | nuclear envelopes reform; in animals, two cells divide to give four haploid cells; in plants, a tetrad of four haploid cells is formed |