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How Cells Divide: Mitosis vs. Meiosis
by Rick Groleau
As viewed from a human perspective, nature has done some
ingenious engineering to overcome some of the obstacles it
has faced. Take the evolution of sex, for instance. To make
the move from asexual to sexual reproduction, nature took a
system by which parent cells reproduced simply by dividing
(asexual reproduction) and altered it to allow two parent
cells to combine to create offspring (sexual reproduction).
It met this challenge by devising (again, speaking from a
human perspective) a system by which parent cells
incorporate genetic information from both of its parents but
contain half the amount of DNA. With only half the DNA, when
the parent cell combines with another parent cell, the
proper amount of DNA is maintained. This solution is called
meiosis.
Mitosis describes the process by which the nucleus of a cell
divides to create two new nuclei, each containing an
identical copy of DNA. (Cytokinesis describes the division
of the rest of the cell.) Almost all of the DNA duplication
in your body is carried out through mitosis. Meiosis, as
described above, is the process by which certain sex cells
are created. If you're male, your body uses meiosis to
create sperm cells; if you're female, it uses meiosis to
create egg cells. Others cells in your body contain 46
chromosomes: 23 from your father and 23 from your mother.
Your egg (or sperm) cells contain only half that
number—a total of 23 chromosomes. When an egg and
sperm unite to make a fertilized egg, the chromosomes add up
to equal 46.
How exactly does meiosis mix and halve chromosomes? Find out
through this feature, which provides a step-by-step,
side-by-side comparison of meiosis and mitosis.
Rick Groleau is managing editor of NOVA Online.
The 18 Ways (And Then Some)
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On Human Cloning
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Fertility Throughout Life
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How Cells Divide
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