The genetic analysis of familial traits - III. Matings involving one parent exhibiting a trait determined by a single recessive gene substitution with special reference to sex-linked conditions
The present communication discusses the quantitative analysis of matings involving one affected parent, when a clinical condition is determined by a single recessive gene substitution.
The proportion of matings showing direct transmission is higher than would be calculated from the theory of random mating. One reason for this is that the application of a theory of random mating is limited by the geographical propinquity of the individuals concerned. There must, therefore, be a limit of dilution beyond which increasing rarity of the trait does not appreciably decrease the probability that an affected individual will mate with a carrier.
Matings of albinos with normal individuals having affected offspring satisfy the hypothesis that albinism is determined by a single recessive autosomal gene substitution. The discrepancy for matings of two normal parents with some albino offspring is not significant for large families, and may hence be attributed to biased selection of the small families recorded.
There are very few exceptions to the rule that all types of matings in stocks displaying red-green colour blindness conform to the requirements of the hypothesis that the condition is determined by a single recessive gene substitution on theX-chromosome.
As far as the extant evidence can be regarded as trustworthy, haemophilia must be interpreted as a recessive sex-linked condition which is alsosex limited.
There are two forms of Leber’s disease, both genetical types being found among Europeans and probably both among Japanese, though the majority of examples of the recessive sex-linked form are European and the majority of the Japanese cases are of the type which is apparently determined by two autosomal dominant genes.
Volume 100, 2021
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