Final answer:
A successful mutation in evolution must occur in the germplasm's DNA.
Step-by-step explanation:
In order for a mutation to be successful in evolution, it must occur in the germplasm's DNA. Germplasm refers to the genetic material present in the reproductive cells (eggs and sperm) that can be passed on to offspring. Mutations in the germplasm's DNA can lead to genetic variations, which are the basis for natural selection and evolution.