missing patches of hair

so i had a litter of rats that all seem to have little patches of thin or missing hair. is this a genetic thing or is there something wrong here. ill try and get pictures posted up tomorrow, but im drinving to georgia so ima most likely be occupied all day. it isnt a huge concern as they are bound to be feeders, just would like to get a clue as to what it is.

Was the breeding done with 2 rex rats, making some of the babies double rexes?

nope just plain ol rats!

it's possible that it's genetic, or maybe there was a bit of a scuffle between them? if all else seems fine, then they're more then likely okay. (i.e. eating, acting normal, drinking, no runny noses or couging, etc.)

yeah i figured that it might be genetic. but their fur is really soft even though its a little thin