PRINCIPLES OF HEREDITY 



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of genes in the guinea pig governs the length of the hair in the coat; the 

 gene for short hair (S) is dominant to the gene for long hair (s). The 

 genes for hair color and hair length are located in different chromosomes. 

 Each guinea pig has two of each kind of gene; thus the genotype of a 

 homozygous black, short-haired animal is BBSS and the genotype of 

 a homozygous brown, long-haired animal is bbss. The black, short-haired 

 animal produces only one kind of gamete, for all of them are BS. Simi- 

 larly, the brown, long-haired animals produce only bs eggs or sperm. 



The mating of a black, short-haired animal with a brown, long- 

 haired one produces offspring all of which have short, black hair; they 



Block, Short-holred 



Brown, Long-hoired 



3 Brown, Short-hoired 



1 Brown, Long -haired 



Figure 32 2 An example of a dihybrid cross: the mating of a black, short-haired 

 guinea pig and a brown, long-haired one, illustrating independent assortment. (Villee: 

 Biology.) 



