TABOO AND GENETICS 73 



an H will unite with another H or with an ^ — 

 that an A will unite with an H or another A. 

 Thus we have two chances of getting HA to 

 each chance of getting either A A or HH. Half 

 the zygotes will be HA, one-fourth HH and 

 one-fourth A A. 



If we consider four average males, one wiU 

 have two A's (absence of the factor for horns) 

 and will thus be hornless. One will have two 

 H's, or the double factor for horns, and hence 

 will exhibit horns — as will also the two HA's 

 since a single dose of horns expresses them in 

 a male. So we have the three-to-one Mendehan 

 ratio. ' 



But four females with exactly the same 

 factors will express them as follows : The one 

 HH (double factor for horns) proves sufficient to 

 express horns, even in a female. The AA, 

 lacking the factor entirely, cannot have horns. 

 Nor will the two HA females have horns, a 

 single dose being insufficient to express them 

 in a female. Again we get our three-to-one 

 Mendehan ratio, but this time it is three hornless 

 to one horned. 



Especially Goldschmidt's carefully graded 

 experiments point to a similar difference in 

 the strength of the dose or doses of the sex 

 factors. Instead of the two doses of horns 

 required to express them in the presence of the 

 female secretory balance in Professor Wood's 



