Ectrodactyly‐evidence in favour of a disturbed segregation in the offspring of affected males

Summary A pedigree of ectrodactyly, first published by Prof. Karl Pearson in 1908, is brought up‐to‐date. The excess of affected over unaffected offspring on a single dominant gene hypothesis has been maintained. This excess is apparently determined entirely by a marked preponderance of affected sons of affected fathers. It is shown by analysis of other large pedigrees of this condition that in sum this excess of affected over unaffected sons of affected fathers is highly significant technically. If this finding is not due to chance then the most likely explanation of the phenomenon appears to be germinal selection. Some implications of the acceptance of the validity of the data and of explaining them in this way are briefly discussed.