GENERAL RELATIONS IN INHERITANCE 305 



(deep red, intermediate in size and form between the par- 

 ents). In F2 and later generations there were at least 24 

 different combinations of diverse sizes, forms and colors. 

 From the two original stocks, 24 genetically diverse stocks 

 had been formed by crossing. 



The same kind of consequences follow upon crossing di- 

 verse stocks in animals. As an example the somewhat com- 

 plex case of different varieties of rabbits may be taken. In 

 domesticated rabbits there are large numbers of varieties 

 differing in their coat colors, as well as in other features. 

 As to the probable origin of these many varieties we may 

 summarize the account of Nachtshelm.'* 



In the wild rabbit it is known that many pairs of genes 

 interact to produce the brownish gray color of the hairy 

 coat. This coat color includes four or more colors — black, 

 brown, yellow, bluish — disposed in zones on the individual 

 hairs; together they give the general brownish-gray effect. 

 It is known that five pairs of genes play important roles in 

 producing these colors; these five are designated by five 

 letters of the alphabet. In the wild rabbit all these genes 

 are in the dominant condition, so that for them the capital 

 letters are employed. Thus, so far as these five pairs of 

 genes are concerned, the wild rabbit has the genetic consti- 

 tution AABBCCDDGG. (Other genes affect the coat color; 

 for present purposes these may be left out of account.) 



Nachtsheim shows that somewhat more than a century 

 ago there were five varieties differing in color from the 

 wild type. Each one differed by a change in the genes of 

 one of the five pairs. When the genes AA are changed to 

 the recessive condition aa, no color is produced, so that this 

 yields a white (that is, colorless) variety. When BB is 

 changed to recessive bb, there is no dark pigment produced, 

 giving animals of a "yellow-silver" color. When GG is 

 changed to gg, the color is no longer distributed in zones 

 on the hairs, but covers them completely. In such a case 



