54 A MANUAL OF MENDELISM 



with other factors which have to do with the distribution 

 of colour over all the body and with its restriction to 

 the parts mentioned above. In this case it is not a 

 factor for whiteness which is dominant to another for 

 blackness, but a factor which restricts the distribution 

 of colour dominant to another which allows it to be 

 fully distributed. 



We may also consider a case in which suppression is 

 not entirely complete, the details of which are to be 

 found in the " Reports to the Evolution Committee of 

 the Royal Society " and in Professors Bateson's and 

 Punnett's volumes on Mendelism. We saw in the last 

 chapter that there are two pairs of factors operating 

 among fowls' combs to produce the four different kinds : 



Walnut XY 



Rose X y 



Pea xY 



Single X y 



But there are other kinds of combs mateable with 

 these, and, therefore, other pairs of characters. Pro- 

 fessors Bateson and Punnett found two other kinds. 

 One, which was an ordinary single comb excepting that 

 it was split in two, was brought from Cairo. This comb 

 was mated with the ordinary single comb, over which it 

 " proved to be a distinct dominant." That is to say, 

 their progeny were split single combs. The parents 

 differed in one pair of characters only. Both had 

 single combs, and carried therefore the characters xy ; 

 but the Cairo comb carried a factor for splitting which 

 was dominant to a factor for non-splitting in the 

 ordinary single comb. If we call this new pair of 

 factors S and s, then the characters of the Cairo and the 



