Recessive and Sporadic Rumplessness of Fowl: Effects on Penetrance and Expressivity

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Abstract
Recessive rumplessness in a stock of white leghorn fowl showed low penetrance and expressivity. The white leghorn stock produced 1.6 percent of sporadic rumplessness. The incidence of sporadic rumplessness was 4.15 percent in silver gray dorking fowl and 0.98 percent in jungle fowl. In descendants of crosses between recessive rumpless and dorking fowl penetrance as well as expressivity of recessive rumplessness were significantly raised. In descendants of crosses between recessive rumpless and jungle fowl penetrance of recessive rumplessness was significantly lowered. It is suggested that sporadic rumplessness is brought about by hereditary factors which ordinarily are insufficient to interfere with normal development, but which may become a part of the hereditary mechanism for polyfactorially-transmitted traits.