272 EVOLUTION, GENETICS, AND EUGENICS 



COAT COLORS IN GUINEA PIGS 



In guinea pigs the wild type coloration is a kind of reddish-gray 

 mixture called "agouti." There are also black coat colors and whites 

 (albinos). 



Agouti, when crossed with some types of white, gives all agouti in 

 the F x generation, and 3 agouti to 1 white in the F 2 generation. A 

 black guinea pig crossed with agouti gives all agouti in the F 1} and 3 

 agouti to 1 black in the F 2 generation. Evidently both black and 

 white are recessives to agouti; so agouti must be due to at least two 

 dominant color factors, A and C. 



If we assume that A is a dominant factor, whose recessive allelo- 

 morph, a, gives black color; and that C is a dominant factor whose 

 recessive allelomorph, c, gives white color, then we may put down the 

 formulas for the genetic composition of the three coat colors as follows: 



yL 4 CC = agouti 

 AAcc = albino (of one kind) 

 aaCC — black 



Then when black (aaCC) is crossed with white (A Ace), all of the F t 

 generation would be agouti and the F 2 ratio would be as follows: 



9 A A CC= agouti 

 3 .4.4 cc= white 



3 a aCC= black 

 1 aacc = white 



This would give a phenotypk ratio of 9 agouti to 3 blacks to 4 whites, 

 another rather slight but unusual modification of the familiar 9:3:3:1 

 ratio, due to the fact that the phenotype "white" consists of two geno- 

 types. 



Characters that seemed quite simple at first have been found, by 

 methods similar to those here presented, to be complex when subjected 

 to analysis. Such apparently simple characters as human eye color 

 and hair color, though never fully analyzed, would doubtless amply 

 repay investigation. If we knew as much about these characters as 

 we do about some animal characters, the testimony of a geneticist in a 

 paternity case would be more valuable than it is at present. 



