Is Syndactyly Genetic?

The best answer here is yes, no and sort-of:

Most cases of syndactyly, that are not associated with a syndrome, are sporadic or without a known genetic relationship. Said another way, every child has an equal chance of being born with an isolated syndactyly- most commonly of the long and ring fingers.

It is estimated that between 10 and 40% of cases are passed on genetically, mist commonly from the paternal side and more frequently passed from to males than females. Although syndactyly may be autosomal dominant, meaning there is a 50% chance of an affected family member passing on the gene, it is variably expressed and penetrance is incomplete. This means that syndactyly will often skip a generation or present in different forms from previous affected family members.