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 



F, 



H X h X hornless ? 

 H h X horned 6 



Gametes f Eggs H X — hX 



ofFi l^permH 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 : 



Fy Hornless 9 H X — hx 

 Hornless 6 h x — h 



h X H X hornless 9 



h X h X hornless ? 



h H X horned S 



h h X hornless 6 



