[Absence of the palmar c triradius. Dermatoglyphic and geneologic study of a genetic character transmitted since the 17th century in a Quebec family].

A dermatoglyphic research on the absence of the palmar c-triradius was carried out in a Canadian family line originating from a French married couple who settled in the Quebec City area in 1649. Of the 51 individuals examined, 34 showed that c-triradius was missing on one or both palms. The study of the family tree and of the data confirms the hypothesis that an absent palmar c-triradius is an autosomal dominant trait transmitted by an heterozygous genotype with, in the present observation, an incidence of 66,6% and an estimated penetrance of 44,1%.