The familial incidence of "grey" Afrikander calves with and without goitre

Afrikander cows rarely drop "grey" (very pale yellow) calves with or without goitre. These 2 defects have been recorded among calves in 2 herds. In one of these herds, all affected calves were the progeny of a particular bull when bred to its own daughters and closely related cows. The bull responsible on the other farm apparently inherited the pathogenic genes for goitre and grey colour also from his paternal and maternal ancestry respectively. Both sires are fairly closely related. Both bulls and the cows they sired must have been heterozygous for both abnormal genes to produce homozygous offspring. There is evidence that the factors concerned segregate according to Mendelian rules during the second generation. These anomalies appear to be simple (autosomal) recessive genes and when combined in the same animal, are usually lethal.