In humans, one allele of the APOE gene, called APOE–ε2, can result in a high tolerance of cholesterol. Cholesterol is a vital substance for humans but may lead to heart disease in an older adult with a history of high cholesterol diets. High cholesterol diets are becoming more prevalent in the United States. Currently only about 2% of humans carry the APOE–ε2 allele. Which of the following states a valid null hypothesis about the future distribution of APOE alleles in future generations in the United States?单项选择题

A

The variant protects an individual from a condition that is only common among humans beyond reproductive age, so the frequency of the allele will likely not change much in the future because it is not influenced by natural selection.

B

As high cholesterol diets become more common in the United States, individuals with the APOE–ε2 allele will have a better survival rate from heart disease than those without the allele, so the allele will increase in frequency.

C

The low frequency of the APOE–ε2 allele indicates it is probably a recessive allele, so it will become less frequent as the dominant allele becomes more frequent.

D

The APOE–ε2 allele was the result of chance mutations so it is not possible to predict how its frequency will change in the future.

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A group of people whose ancestors immigrated to North America 200 years ago have certain allele frequencies that differ significantly from those in surrounding populations in the United States. Which of the following is the most likely explanation for the difference in allele frequencies?

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