Sickle cell anemia is a disease involving abnormally shaped red blood cells,
which then have difficulty circulating properly through the body. It is caused
by a one nucleotide substitution in one gene. This is a recessive mutation,
meaning that the disease only develops when both copies of the gene (one on each
duplicate chromosome) contain the substitution. Interestingly, people with only
one copy of the mutation (who thus have normal red blood cells) show an
increased resistance to malaria.
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