Bill and Bob are biological twins who were adopted as babies. Their adoptive father, paternal grandfather, and paternal great-grandfather all suffered from early-onset fingernail greening. Which of the following statements is MOST likely to be the case?

We know from the prompt that Bill and Bob are adopted; therefore, they do not share their genetics with their adoptive father. It’s also very likely that since three generations of the males in the family of their adoptive father have green nails so the disease should be a genetic trait, rather than one determined by their environment.