What is the most reliable indicator that a chimera can pass a targeted mutation through the germline?

• A. Patchy fur
• B. Offspring inheritance of the mutation
• C. The chimeric mouse's weight
• D. Eye color

Answer: (B)

Germline transmission depends on the mutated stem cells contributing to the gonads and producing gametes that carry the mutation. The clearest, most reliable sign is seeing the mutation in the offspring after breeding the chimera. If progeny inherit the mutation, it demonstrates that the chimera’s germ cells carry the change and can pass it to the next generation.

Somatic indicators like patchy fur reflect mosaicism in non-reproductive tissues and do not guarantee that the germline carries the mutation. Traits such as weight or eye color aren’t reliable indicators of germline status and don’t inform whether the mutation is present in reproductive cells.