In a disease associated with a nucleotide repeat, anticipation is often noticed in subsequent generations, usually associated with a more severe phenotype. Which of the following is a more likely cause of anticipation?
A)The CAG alleles with a high number of repeats are unstable and change size from generation to generation.
B)Subtle phenotypic nuances are more often sought by a physician.
C)Family members are exposed to the same mutagens.
D)Highly repeated sequences are expressed more often.
E)The sequences have greater stability in later generations.

Question

Quizplus · Accepted Answer

Nucleotide repeat diseases, such as Huntington's disease, are caused by unstable CAG repeats, which tend to expand in size from one generation to the next, resulting in a more severe phenotype. This is known as anticipation, and it is thought to be caused by the increased instability of the CAG repeat alleles with higher numbers of repeats. Subtle phenotypic nuances (B) or exposure to mutagens (C) are not likely causes of anticipation, and there is no evidence to suggest that highly repeated sequences (D) are expressed more often or that the sequences become more stable (E) in later generations.

In a Disease Associated with a Nucleotide Repeat, Anticipation Is