There is no gene "for" such unambiguous bits of morphology...

There is no gene "for" such unambiguous bits of morphology as your left kneecap or your fingernail. [...] Hundreds of genes contribute to the building of most body parts and their action is channeled through a kaleidoscopic series of environmental influences: embryonic and postnatal, internal and external. Parts are not translated genes, and selection doesn't even work directly on parts.