Cat Genetics. So simple, yet so complicated. Let's see how short-furred and long-furred genes get passed down. Let's use the Firestar family.
Redtail and Brindleface - Brindleface is short-furred, while Redtail is obviously long-furred. Brindleface has the long-furred gene via Fuzzypelt, and Redtail has the short-furred gene via Swiftbreeze.
Nutmeg - She is short-furred, and it is unknown whether she has the opposite gene.
Firestar, Princess, Luna, Filou, and Tommy - Firestar and Filou are both short-furred, and Princess, Luna, and Tommy are all long-furred, indicating that one or both of their parents may have the long-furred gene.
Oliver - Long-furred. Unknown whether he has the opposite gene.
Cloudtail - Is long-furred, but carries the short-furred gene via Jake and Nutmeg.
That's it for now, because I'm lazy. :P
PS: I dunno if these are controlled by genes, but whatever.