alleryStart learning →Huntington's disease is caused by a dominant lethal allele. Why does it persist in human populations?
ACarriers pass it on before symptoms begin
BCarriers are protected by a second allele
CThe allele arises fresh in every generation
DOnly homozygous individuals ever fall ill
Answer & Solution
Correct answer: A. Carriers pass it on before symptoms begin
1. People heterozygous for the dominant Huntington allele will inevitably develop the fatal disease.
2. Onset may not occur until age 40, which is well past the start of reproductive life.
3. By then a carrier may already have passed the allele to 50 percent of their offspring.
4. The allele therefore survives even though it is eventually fatal in every carrier.
5. A second wild-type allele offers no protection, because the lethal allele is dominant.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 12 "Mendel's Experiments and Heredity", section 12.2 Characteristics and Traits_
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