Genetic fallacies are similar to ad hominem fallacies in that they are both fallacies of relevance that focus on the source of an argument rather than criticizing it in terms of facts and reasoning. However, there is a difference:
Ad hominem fallacies focus on whoever is currently presenting an argument as the sole basis for rejecting it.
Genetic fallacies focus on the original sources of an argument (e.g., people, cultures, movements) as the sole basis for rejecting it.