HEREDITY AND SEX 189 



only barred offspring. When the male Barred Rock is 

 bred with a non-barred variety, the offspring of both 

 sexes are all barred. If the female Barred Rock is mated 

 with non-barred breed, the offspring will be about one- 

 half barred and the remainder non-barred. The barred 

 offspring are always males, while all the females are non- 

 barred. The barred character is, therefore, sex-limited. 

 The Barred Rock female is heterozygous and the male 

 homozygous. The pure Barred Rock breed transmits 

 the barred quality because the male is pure in respect to 

 the barred character. The same result follows if a cross- 

 barred male is mated with barred females. The explana- 

 tion of sex-linked inheritance is probably to be found in 

 the existence of some plus element in the egg which is 

 not found in the sperm. 



179. Controlling the sex of offspring. In many of 

 the domestic animals, the sex of the individual determines 

 its peculiar value and usefulness to mankind. If some 

 method of breeding could be devised which would result 

 in the production of the particular sex desired, it would 

 be a great economic gain. That such attempts have 

 been made by both ancient and modern breeders is made 

 clear from an examination of the literature of the subject 

 from the earliest times to the present. Because of the 

 more or less general belief among practical breeders in 

 the possibility of controlling sex, it seems necessary to 

 consider briefly some of the more widely held theories of 

 sex control. 



180. Age or vigor of parents. Two investigators, 

 Sadler l (1830) in England and Hofaker (1823) in Ger- 

 many, collected statistics representing more than 2000 

 births. Their statistics showed that when the father is 



1 Carpenter, "Human Physiology," p. 1015. 



