COLOR AND COAT CHARACTERS. 19 



The tables show that the wild agouti has been kept in a heterozygous 

 condition up to the -jV wild females. Matings made since these tables 

 were constructed prove the same up through the yfg- wild, i. e., for 

 seven generations. In other words, one dose of agouti was received 

 from a wild race, and this one dose was handed on for seven generations; 

 and each female that received it passed it on to one-half of her offspring 

 in the next more dilute generation. Also, one dose of agouti derived 

 from tame guinea-pigs was given to some ^-V wild hybrids, and this 

 was similarly inherited for three generations. In all these cases, agouti 

 may be said to act as a unit character, just as in the well-known tame 

 crosses. 



Summarizing all the matings of all generations of hybrids (table 11), 

 in which one parent is heterozygous in agouti and the other is recessive, 

 such matings have produced 226 agoutis and 214 non-agoutis. The 

 most probable expectation is 220 of each sort. A departure of 6 

 individuals is expUcable by the law of chance.^ 



HETEROZYGOUS AGOUTIS MATED INTER SE. 



The matings of female hybrids, heterozygous in agouti, to male 

 guinea-pigs, likewise heterozygous in agouti, are of very limited number, 

 but more are in progress at the present time. Eight female hybrids, 

 known to be heterozygous, were mated to 5 different male guinea-pigs, 

 also heterozygous. The results of these 8 matings (table 12) are 36 off- 

 spring, of which 32 are agouti and 4 non-agouti. The most probable 

 expectation is 27 agoutis to 9 non-agoutis. In these matings, cf 1436, 

 cf 2196, and cf 2002 did not produce any recessives, yet table 8 shows 

 that 0^2196 and cr2002 were heterozygous. Male 1436 is known to 

 be heterozygous from pedigree, so that his 4 agouti young (table 12) 

 do not indicate any error. Male 1917 (table 12) produced 9 agoutis 

 and only 1 non-agouti. The ratio 32 : 4 shows a considerable excess of 

 agoutis over the usual 3:1. Such deviations are usually explained by 

 the Law of Error, according to which any ratio might be obtained in 

 place of a 3 : 1 ; but the wide departures from such a ratio must occur 

 with minimum frequency. Possibly the deviations observed in this 

 case are due to chance. 



In mating heterozygotes inter se we expect two visible classes, but 

 three actual zygotic classes. One-third of the agouti individuals should 

 breed true; two-thirds should be heterozygous; the recessives should 

 breed true. To test the validity of the ratio, the breeding records of 

 the agouti animals produced by the experiment of table 12 have been 

 studied. It was possible to mate 12 agouti females and 1 fertile agouti 

 male to non-agouti guinea-pigs. The rest of the 32 agouti animals 



'Since these records were made, 103 young have been born in crosses similar to those above. 

 Of these young, 46 were agoutis and 57 were non-agoutis. Adding these to those previously 

 obtained, we have a ratio of 272 agoutis to 271 non-agoutis — actually the most probable expectation. 



