34 GENETIC STUDIES ON A CAVY SPECIES CROSS 



Tables 31 to 36 record all the matings of wild hybrid females, from 

 the I wild up through the -^ wild, in which at least one member of each 

 cross was homozygous in the extension factor. Combined, all these 

 matings produced 628 offspring with extended pigmentation (table 

 37). The conclusion is obvious: extension is epistatic to restriction in 

 hybrids of various blood-dilutions, precisely as among guinea-pigs. 



HETEROZYGOUS CONDITION OF EXTENSION CROSSED WITH RESTRICTION. 



Regressing, it will be recalled that 3 guinea-pig males carrying re- 

 striction were mated to some f wild females. The matings produced 

 29 offspring (table 31), of which some should be heterozygous. These 

 J wild offspring were the first that could be used to establish a red race 

 of hybrids. When two of these were mated with recessive, red guinea- 

 pig males, they produced red-coated as well as black-coated young, in 

 the ratio 9 : 10 (table 38). This result fulfills the conditions of most 

 probable expectation. It shows clearly that the j wild individuals can 

 form gametes of two kinds, one of which bears the maternal character 

 extension, and the other the paternal character, restriction, received 

 from the tame stock. 



Two classes of matings (table 39) were made among the \ wild 

 females, which should yield animals of extended pigmentation and 

 restricted pigmentation in approximately equal numbers : 



(1) Female hybrids, heterozygous in extension (produced in matings 

 recorded in tables 32 and 38), were mated to red guinea-pig males. 



(2) Red female hybrids, lacking entirely the extended coat (produced 

 in matings recorded in table 38), were mated to guinea-pig males, 

 heterozygous in extension. Similar matings were made among ^V '^Id 

 hybrids (table 40), -5^ wild hybrids (table 41), and -^ wild hybrids 

 (table 41). The summary of all these matings is given in table 42, 

 The offspring fall into the two expected classes: (1) animals with an 

 extended coat pigmentation, Ee, yet heterozygous in extension; 

 (2) animals of red or restricted coat pigmentation, ee. The classes 

 should occur in approximate equality. The ratio 47 : 55 is so close to 

 the most probable expectation, 51 : 51, as scarcely to require comment. 

 Segregation as regards the extension factor evidently occurs among the 

 hybrids just as among guinea-pigs. The brown-eyed red guinea-pig 

 represents a combination of three recessive color characters which 

 segregate independently in crosses of one variety of guinea-pig with 

 another. They behaved in the same way in crosses between C. rufes- 

 cens (or its guinea-pig hybrids) and the guinea-pig. Yet segregation 

 and recombination of these several color characters is without apparent 

 influence on the fertility of the hybrids. One color variety of hybrid is 

 no more fertile than another. 



