Reappearance of the multiple trait semilethal mutation (psp) in the fowl.

The multiple trait semilethal mutation previously described by McGibbon and Shackelford (1972) has reappeared among the F2 progeny of an outcross mating between two standard lines. The mutant phenotype is expressed by the simultaneous presence of syndactyly polydactyly, and ptilopody resulting from homozygosity for an autosomal recessive gene, psp. Less than 31% of the mutants hatched, with the rest dying during the last quarter of the incubation period. In this study no psp/psp chicks survived beyond 6 weeks of age.