Evidence for a major gene effect in the distributions of digital ridge counts

Previous attempts to isolate major gene effects in digital dermatoglyphics have been approached from two main directions. One has been concerned with analysing the components of total ridge count (TRC) distributions and examining various parameters of these distributions. The other has concentrated on the inheritance of various combinations of digital patterns. This study is primarily concerned with the shape of TRC and digital ridge count distributions. It suggests that a major gene effect may be as conspicuous in the distributions of digital counts as it is in TRC if these are viewed from the standpoint of global variation. The relationship between mean TRC, the standard deviation of TRC, skewness and kurtosis is examined and the results are compared with those obtained from a simple major locus model in which the overall distribution of TRC is composed of three overlapping normal distributions. As predicted by the model there is a negative correlation between mean TRC and its standard deviation, also a positive correlation with kurtosis. The expected relationship between mean TRC and skewness is non-linear, taking the form of an asymmetric U-shaped curve. There is evidence that the relationship between mean TRC and g1 in population samples covering a wide range of mean total ridge count follows this trend. The concordance between the predicted relationships and the observed frequency distributions is taken as evidence in favour of a single major locus hypothesis.