ii2 Scientific Proceedings (112). 



embryonic stages. This suggestion was therefore made by Castle 

 and Little (1910) and has since been supported by the histological 

 and embryological findings of Kirkham, Ibsen and others. 

 The case may be diagrammed as follows : 

 A y = yellow 

 A = black agouti. 

 (Yellow carrying black agouti) X (yellow carrying black agouti) 



A y A X A y A. 

 A y A y homozygous yellow dies. 

 Forms -l 2A y A yellows carrying black agouti. 

 A A black agouti. 

 Sex-linked inheritance is slightly more complicated but has 

 been completely demonstrated. The approximate equality of 

 male and female individuals which characterizes most species of 

 the higher animals, is strongly suggestive of the 1 : 1 mendelian 

 ratio. This ratio is obtained in mendelian inheritance when a 

 DR individual is crossed with either a DD or an RR individual. 

 The condition found in- mammals suggests that the female is 

 DD, the male DR in constitution. Evidence for this is derived 

 from the peculiar behavior of certain color characters in inheri- 

 tance. One of the clearest of these cases is seen in cats. Here 

 black and yellow coat color represent alternative or allelomorphic 

 conditions. 



When a black female cat is crossed with a yellow male, two 

 classes of progeny are produced. These are black males and 

 tortoise shell (blotched yellow and black) females. There has 

 been a "criss cross" type of inheritance in which all the sons 

 resemble the mother. This case has been explained on the sup- 

 position that there is linkage in inheritance between the factors 

 determining yellow or black coat color and the substances desig- 

 nated X, which are supposed to be intimately connected with the 

 determination of sex. 



Thus if B y = the factor for yellow. 

 B = the factor for black. 

 BX BX = black female. 

 B y X — = yellow male. 



2 B y X BX = tortoise-shell females. 

 2 B y X — = black males. 



