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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