Black Mottled Orpington
No, mottling is only expressed in plumage color and does not cause feathering on the legs. Leg feathering is caused by other genes. There are three or more loci that are associated with feathered shanks. One of the loci can have three different alleles. According to Somes, there may also be loci that inhibit feathered shanks in birds that would carry feathered shank genes. There are also loci associated with stubs.
Somewhere in the lineage of your birds there were ancestores that had feathered feet. Your bird's parents may not have feathered feet but their parents or grandparents or etc. did have feathered feet. If your birds have stubs it would be the same scenario.
Remember mottling (mo)is a resessive trait. If you cross your mottled birds to a black, the F1 offspring will not be mottled ( just black) but the F1 will carry one mottling gene. If you backcross an F1 with your mo birds, you will produce some mottled and some black BC1 offspring. This backcross will increase the probability of the BC1 haveing ptilopody (PT) ( feathered shanks). If the F1 do not have PT, crossing the F1 offspring will produce some mo chicks (odds are 1 in 4 will be mo). I do not know the genetics behind the PT in your chicks but I believe the odds are better if you cross F1 to F1 to not produce PT in the F2 offspring. This way you get some MO with no PT.
Edited by Wappoke - 5/19/16 at 4:28am