Why do certain genetic diseases, such as cystic fibrosis, persist at relatively high frequencies in certain populations despite being life-threatening? They confer an evolutionary advantage in specific environments. They are the result of recent mutations with no historical presence. Genetic diseases generally occur randomly and without any pattern. They are related to behavioral and lifestyle choices.
Added by Benjamin R.
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Some genetic diseases persist at higher frequencies because individuals who are carriers (heterozygotes) have a selective advantage in certain environmental contexts. This is called heterozygote advantage or balanced polymorphism. Show more…
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Many lethal genetic disorders such as CF, Huntington's, sickle cell anemia, Tay-Sachs, etc., persist in the human genome. How have these genes survived so many millennia of evolution (why didn't they die out)?
Sri K.
Most genetic diseases are rare because a. each person is unlikely to be a carrier for harmful alleles. b. genetic diseases are usually sex-linked and so uncommon in females. $c .$ genetic diseases are always dominant. $d$ a married couple probably do not carry the same recessive alleles. $e .$ mutation rates in human are low.
Cystic fibrosis (CF) is caused by a genetic mutation resulting in defective proteins in secretory cells, mainly in the epithelial lining of the respiratory tract. The one in every 2,000 Caucasian babies who has the disease is homozygous for the recessive mutant. Although medical treatment is becoming more effective, in the past, most children with CF died before their teens. About 20 Caucasian in 2,000 are carriers of the trait, having one mutant and one normal allele, but they do not develop the disease. According to rules of population genetics, the frequency of the homozygous recessive genotype should be rarer than it is. What is one possible explanation for the unusually high frequency of this allele in Caucasian population?
Emilee F.
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