ix] HEREDITY AND SEX 121 



yellow. A more completely known case is that of 

 horns in Sheep. If a sheep of a breed in which both 

 sexes bear horns is mated with one of a completely 

 hornless breed, among the F^ offspring the rams bear 

 horns and the ewes are hornless. Such F t young bred 

 together give in F 2 both horned and hornless males 

 and females, and all the horned ewes and hornless 

 rams are homozygous and breed true, while the horn- 

 less ewes and horned rams may be either pure or 

 heterozygous. Here we have a clear case of a character 

 which is dominant in one sex (male) and recessive in 

 the other (female). 



In such a case as this it may be said that the 

 character is transmitted independently of sex, but its 

 appearance in heterozygous offspring is modified or 

 controlled by the sex of the individual. Both males 

 and females receive the character alike, but it appears 

 in males while it is suppressed in females of the same 

 constitution. 



In another important group of cases the actual 

 distribution of the character among the offspring is 

 determined by their sex, and a study of such throws 

 important light upon the vexed question of sex-deter- 

 mination and the nature of sex itself. As an instance 

 of this we will first consider one of the best-known 

 examples, that of the inheritance of the variety 

 lacticolor in the common Currant Moth (Abraxas 

 grossulariata). The very rare variety lacticolor is 



