Three Pedigrees for Colour Blindness

THREE pedigrees have been found which are of interest in relation to the two-locus theory of the inheritance of red-green blindness formulated by Waaler 1 and Francesehetti 2 , and summarized by Gates 3 . The present hypothesis suggests two series of alleles with near loci on the X -chromosome, N , r , r′ , p and N′ , g , d′ , d , in which N and N′ stand for the normal genes, r for red anomaly, r′ for red anomaly with darkened red 4 , p for protanopia, g for green anomaly, d′ for deviant or anomalous deuter-anopia 5 , and d for ordinary deuteranopia. The orders of dominance are believed to be as shown above, N and N′ being the most dominant. The two-locus theory is supported by the observation that certain women carrying genes from both series are of normal phenotype 1,2,6,7 , and the discovery all over the world of fewer women defectives 3 than would be expected on the single-locus theory by the calculation given by Ford 8 .