SEX-CHARACTERS IN EVOLUTION 111 



factor by N and its absence or recessive by n, then the 

 male is Nn, while the female is homozygous or NN, 

 But in addition to this it is the male in this case 

 which is heterozygous for sex, and n goes to the 

 male-producing sperms, N to the female-producing. 

 Thus in the mating of normal man witli normal 

 woman the transmission is as follows : — 



Gdmefes n 6 



Nn 6 X NN 9 

 /V 9 X ^/K 



f^n 6 



A//V<^ 



That is all offspring normal, but the males again 

 heterozygous. 



An affected male has the constitution nn, and if he 

 marries a normal woman the descent is as follows : — 



nnd X NN(^ 

 Gametes n^6 -¥ no x N + A/ 



r7N(S /Z/V9 



When a normal male is mated with a heteroz3^gous 

 nN female we get 



/2/VCf X /2/V9 



/ZCT + /V9 X n -^ N 

 I 



Game/'cs 



T 



1 



nn<J nN<3 n/V<^ /VA'9 



that is, half the sons are normal and half colour-bhnd. 



