I've been searching a while for studies, pedigrees, whatever... I can't find information on undercoat inheritance. The information out there is on three genes: length, curl, and wire. I came here because it seems there is the occasional shepherd that lacks their undercoat, though the breed is typically double. How is that? Is it something that sometimes pops up from double-coated parents? Or are they rare because they are just not really used for breeding programs?
Links to dogs with pedigrees or good information on their breeding would be nice, if anyone has any. Information of first-generation mixes to typically double-coat breeds to typically single-coat breeds would help.