Does the given pedigree show a Y-linked dominant trait? !Pedigree I think that since every generation has males affected only, the trait must be Y-linked. Also, since every generation expresses the trait, I think it should be dominant. However, the answer key says that the answer is autosomal dominant. Could someone please clarify this and give a tip on how to recognise the difference?

You're right that this could just as well be Y-linked dominant (althought that is pretty rare due to the small size of the chromosome).

The only reason pointing more towards autosomal dominant is the mention of "extra fingers and toes". Most cases of polydactyly are inherited in an autosomal dominant way.

Does seem like an unfair question, though, since (at least in theory) there's more than one possible answer.