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The Epic Interactive Encyclopedia 1998
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Epic Interactive Encyclopedia, The - 1998 Edition (1998)(Epic Marketing).iso
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Meiosis
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1992-09-03
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In biology, a process of cell division in
which the number of chromosomes in the cell
is halved. It only occurs in eukaryotic
cells, and is part of a life cycle that
involves sexual reproduction because it
allows the genes of two parents to be
combined without the total number of
chromosomes increasing. In sexually
reproducing diploid animals (having two sets
of chromosomes per cell), meiosis occurs
during formation of the gametes (sex cells,
sperm and egg), so that the gametes are
haploid (having only one set of chromosomes).
When the gametes unite during fertilization,
the diploid condition is restored. In plants,
meiosis occurs just before spore formation.
Thus the spores are haploid and in lower
plants such as mosses they develop into a
haploid plant called a gametophyte which
produces the gametes (see alternation of
generations). See also mitosis.