Huntington's disease is caused by a single dominant allele. It is a lethal disease, yet it persists in the human population. Which of the following statements best describes why?
A. Huntington's disease is sex-linked and every human has at least one X chromosome; thus, the chances are extremely high for this allele to be maintained in the human population.
B. While lethal to a parent, Huntington's disease will not be lethal to the offspring since it can skip a generation.
C. Even though Huntington's disease is lethal, it improves chances for reproduction before the person dies.
D. Huntington's disease presents symptoms in midlife, after most people have already had offspring.
E. Huntington's disease can present symptoms so mild that they appear to lack dominant expression of the allele in some individuals; in those cases, the allele is passed on to the offspring.
Answer: D
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