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In sickle cell
anemia,
abnormal
hemoglobin
deforms blood
cells to sickle
shapes.
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Keeping
variety in store |
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| Sexual species
can call on a "library" of locks unavailable to asexual
species. This library is defined by two terms: heterozygosity,
when an organism carries two different forms of a gene,
and polymorphism, when a population contains multiple
forms of a gene. Both are lost when a lineage becomes
inbred. What is the function of heterozygosity? In the
case of sickle cell anemia, the sickle gene helps to defeat
malaria. So where malaria is common, the heterozygotes
(those with one normal gene and one sickle gene) are better
off than the homozygotes (those with a pair of normal
genes or sickle genes) who will suffer from malaria or
anemia. |
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| One of the
main proponents of the Red Queen hypothesis was the late
W. D. Hamilton. In the late 1970s, with the help of two
colleagues from the University of Michigan, Hamilton built
a computer model of sex and disease, a slice of
artificial life. It began with an imaginary population
of 200 creatures, some sexual and some asexual. Death
was random. As expected, the sexual race quickly died
out. In a game between sex and "asex," asex always
wins -- other things being equal. That's because asexual
reproduction is easier, and it's guaranteed to pass genes
on to one's offspring. |
Sea anemones
reproduce
asexually. |
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