PlushSize:
In all honesty, it's not genetic it's more so a source of comfort. If the father beds a thick wife, she gets wider with pregnancy, baby pounds are hard to shed. Kids grow up seeing a thick mother being happy, and it removes the negative stipulations. When i was younger if i was in church and i saw a boy had a fat Mama I'd slide over and start chatting him up about a whole bunch of not very Christian things♥ SSBBW/BBW's were my perfect vision of milf growing up. I wanted to be just like them. Fat and happy!
I think similar case of comfort and endearment especially from a family dynamic. When you are around people with healthy self-esteem, love of self it does rub off. When you're fat but won't be a walking stereotype, or distance from those who see you as lesser than. Jovial fatties do attract more people, though its the downers and borderline small fats you may have to push aside.