Schulz K C, Groenewald J W
J S Afr Vet Assoc. 1983 Sep;54(3):147-54.
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.
非洲瘤牛很少产出带有或不带有甲状腺肿的“灰色”（非常浅黄色）小牛。这两种缺陷在两个牛群的小牛中都有记录。在其中一个牛群中，所有受影响的小牛都是一头特定公牛与其女儿及近亲母牛交配所生的后代。另一个农场的致病公牛显然分别从其父母系祖先那里继承了甲状腺肿和灰色的致病基因。两头种公牛亲缘关系相当近。这两头公牛及其所生的母牛对于这两个异常基因肯定都是杂合子，才能产生纯合子后代。有证据表明，相关因素在第二代中按照孟德尔定律进行分离。这些异常情况似乎是简单的（常染色体）隐性基因，当它们在同一动物中组合时，通常是致命的。
