Final answer:
Unstable trinucleotide repeat alleles can be observed to expand during meiosis in both male and female premutation carriers, as well as during mitosis in individuals with a disease allele, making the correct answer option E Both B and C.
Step-by-step explanation:
Unstable trinucleotide repeat alleles can expand in several contexts related to genetic mechanisms. These expansions can occur during meiosis in both male and female premutation carriers, as well as during mitosis in individuals with a disease allele. Specifically, this means that expansions can be observed:
- During meiosis in a male premutation carrier (A)
- During meiosis in a female premutation carrier (B)
- During mitosis in an individual with a disease allele (C)
Therefore, the correct answer to the question regarding the situations in which unstable trinucleotide repeat alleles can be observed to expand is option E Both B and C, as these mutations can occur in the germline during meiosis as well as in somatic cells during mitosis.