Frequencies of Sex-Linked Red-Green Colour Vision Defects

Abstract

In a research carried out during the last five years on subjects in the west of Scotland, with an apparatus which efficiently discriminates between major (sex-linked) red-green defectives and ordinary colour-weak individuals, 7.8 per cent of male and 0.65 per cent of female sex-linked defectives were found in 464 males and 460 females. This corresponds well with the results of researches in which the Ishihara Test was used^1,2,3. The expected frequency of female defectives would be 0.61 per cent, with 7.8 per cent of males in the population. The observed frequency of 0.65 per cent is not statistically different from this figure, and it suggests that there is little truth in the common belief that there are more colour-blind women in the population than would be expected. The extra ones are heterozygotes, some of whom are doubtful passes on the Ishihara test.