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Sickkle cell anemia is caused by a single codominant gene; it
does not follow the usual pattern of dominant / recessive. A
dominant trait is where the trait occurs if only one chromisome
in a chromisome pair carries the allele (gene) for the trait.
A recessive trait is where both chromisomes in a pair have to
carry the gene in order for the trait to appear. (Chromisomes
are strands of DNA in the nucleus of a cell that determine the
properties of the cell. They always occur in pairs; humans
have 23 pairs) If both the chromisomes in the chromisone pair
that carries the gene have the allele for sicke cell, the person
will have the severe--usually fatal (75%) form of the disease.
If only one of the chromisomes in that pair carries the allele,
the person will be mildly anemic--but will be immune to
falciperum malaria ("blackwater fever"), the most serious form
of malaria, which is usually fatal. There are several other
anemia-like conditions that behave the same way, e.g.
mediterranian anemia.
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alamosaurus
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