I said D for the following question but I got it wrong, I know it's not B though because the disease isn't sex-linked and not C because people who get the disease are usually older (50's). Would the Answer be A then?
Even though it's deadly the huntington's disease allele can remain in the population because:
A)The dominant allele sometimes reverts to a recessive form
B)it's sex linked to the male gamete and females don't carry the allele
C)people with the disorder often live long enough to reproduce
D)it's autosomal and can be masked by a codominant harmless allele
I don't see why it can't be C. Men may "have the disorder" (bad gene) even though symptoms do not show up until middle age, after reproduction.
Read "selection" of
http://evolution.berkeley.edu/evolibrary/article/medicine_05
To determine the correct answer, let's analyze each option.
Option A) The dominant allele sometimes reverts to a recessive form.
This statement does not accurately describe the inheritance pattern of Huntington's disease. Huntington's disease is caused by a dominant allele, not a recessive allele, so this option is not correct.
Option B) It's sex-linked to the male gamete, and females don't carry the allele.
This option is also not correct. Huntington's disease is not sex-linked; it is autosomal, meaning it occurs on chromosomes other than the sex chromosomes.
Option C) People with the disorder often live long enough to reproduce.
This option is partially correct. Individuals with Huntington's disease often experience symptoms later in life, usually in their 30s or 40s, and can still reproduce before the onset of symptoms. However, the disease does not usually manifest until the person is in their 30s or later, which is different from the statement in your question that suggests people in their 50s are typically affected.
Option D) It's autosomal and can be masked by a codominant harmless allele.
This option provides the most accurate explanation. Huntington's disease is an autosomal disorder, meaning it is located on non-sex chromosomes. Additionally, individuals with the disease carry a dominant allele, whereas individuals without the disease carry a codominant harmless allele. Therefore, the presence of the harmless allele masks the disease allele in carriers, allowing it to remain in the population.
Based on the analysis, it appears that Option D is the correct answer. Therefore, your initial assumption that the answer would be A is incorrect.