138 



HEREDITY AND SEX 



carried by the female-producing sperm. The analysis 

 is then as follows: One ''dose" of horns (H) in the 

 male produces horns, but two doses are necessary for 

 the female. 



Hornless ? hX — hX 



Horned S H X — H 



Fi 



H X h X hornless ? 

 H h X horned 6 



Gametes 

 of Fi 



Eggs HX — hX 

 Sperm H X — hX — H 



h 



F2 Females 



H X H X horned 

 H X h X hornless 

 h X H X hornless 

 h X h X hornless 



F2 Males 

 H H X horned 

 H h X horned 

 h H X horned 

 h h X hornless 



As pointed out by Punnett a test of the correctness 

 of this interpretation is found by breeding the Fi 

 hornless female to a hornless male (of a hornless breed) . 

 It is assumed that such a female carries the factors for 

 horns in a heterozygous condition ; if so, then half of 

 her sons should have horns, as the following analysis 

 shows : 



H X — hX 



hX — h 



Fi Hornless ? 

 Hornless 3 



h X H X hornless 9 



h X h X hornless ? 



h H X horned c? 



h h X hornless 3 



