ABNORMAL INHERITANCE 



45 



dominant-spotted animal which dies of anaemia (115), two 

 dominant spotted (heterozygotes), and one non-dominant- 

 spotted animal. Strains of dominant spotting exist which 

 throw self animals as recessives. (See Fig. 21.) These are 

 the non-dominant-spotted class. Other strains, known as 

 black-eyed whites, are homozygous for recessive spotting 

 and consequently produce piebald animals instead of selfs, 

 as the non-dominant-spotted class. 



Hereditary Sterility. Dominant hairless (naked) individ- 

 uals which are heterozygous are often produced, but are 

 usually sterile. In one case a homozygous naked female pro- 

 duced young but had no milk to nurse them. Possibly the 

 mutation which affected the hair follicles also disturbed the 



Gametes 



N 



N 



Gametes 



processes of mammary development or secretion. Dominant 

 hairless stocks are maintained by mating heterozygous indi- 

 viduals with each other or by mating heterozygotes to 

 normals. In both types of cross one half the progeny are 

 wasters, that is, are not of the desired type, heterozygous 

 naked. 



Gametes 



N 



Gametes 



Recessive hairless usually produces sterile females and 

 fertile males and hence the strain is readily preserved by 



