WHEN CHARACTERS ARE COMBINED I/ 



Again, when he takes a pure-bred guinea pig with short 

 hair and gives it a mate with long hair, each small guinea 

 pig in the next generation, whatever its color may be, has 

 short hair. This means that short hair is dominant, long 

 hair recessive. Thus it turns out that, with guinea pigs, as 



THREE GENERATIONS OF GUINEA PIGS 



The first row shows a white, smooth-coated father, a black, smooth-coated mother, 

 and their children. Each one of these is black and has a smooth coat. The second 

 row shows a pair of these black hybrid children. The third row shows grandchildren 

 who were children of the hybrids. Notice the white one among them. It resem- 

 bles its grandfather. (From photographs furnished by Professor W. E. Castle of 

 Harvard University) 



he says, " black is dominant over white, rough coat over 

 smooth coat, short coat over long coat." 



By knowing these facts Dr. Castle is able to mate his 

 guinea pigs in such wise as to secure precisely the kind of 

 descendants he wishes them to have. They will be black or 

 white, with long coat or with short coat, with rough coat or 



