Meiosis has eight stages and results in the formation of gametes
(sex cells with half the number of chromosomes of a normal cell).
- Prophase I of meiosis is similar
to prophase of mitosis. The difference is that homologous
chromosomes (each homologue is from a different parent) attach to
form tetrads. The exchange of genetic material between
homologous chromosomes, or crossing-over, occurs.
- In metaphase I tetrads line up in
the middle of the cell and spindle fibers attach to each centromere.
- In anaphase I one homologue is
pulled to each pole.
- In telophase I the nuclei are
reorganized and the chromosomes are decondensed. This phase is
followed by a special meiotic interphase where no DNA
replication occurs.
- In prophase II the nucleus
disappears and the chromosomes condense.
- In metaphase II the chromosomes
line up in the middle of the cell and the spindle fibers attach to
kinetichore proteins.
- In anaphase II the chromosomes
separate and the chromatids are pulled to the poles. Each cell now has
half as many chromosomes as it used to.
- In telophase II the nucleus is
reorganized, the chromosomes are decondensed, the centrioles do not
replicate, and the cell remains in the G1 phase.
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