Sarah Silverman recently said that she wasn't going to have children, because she didn't want to pass on the gene for depression. Anna Brezlaw adds her own commentary at Jezebel. 

My own family tree is littered with alcoholics and depressives, as well as people with unusal smarts and musical ability. Steve's family is pretty similar. Then we mated. Apparently, some recessive autism genes lurked in there, too.

Do I worry about my grandchildren and my great neices and nephews? Sometimes, but not really. I doubt that anybody really has "clean" DNA without any freaky genes in there. Honestly, I wish I had more freaky-gened children, because the two that we made are so great.