COLOR AND COAT CHARACTERS. 31 



Among the guinea-pig males used in these matings were 3 brown- 

 pigmented individuals, viz, cf 617, cf9246, and cf NW, which sired in 

 all 24 1 wild offspring. These, though black-pigmented like the i wild 

 mothers, were heterozygous for that character, and would therefore be 

 expected to transmit black in only half of their gametes, the remainder 

 transmitting, instead the recessive condition, brown. The sequel justi- 

 fied this expectation, as we shall see. 



The experiments with homozygous black may be divided into two 

 groups, both of which produce only black young. The groups are: 



(1) Matings of hybrid females, homozygous, heterozygous, or lacking 

 black, with guinea-pig males which were homozygous in this factor. 



(2) The reciprocal crosses in which the guinea-pig males were hetero- 

 zygous or lacking black, but the female hybrids were homozygous in 

 this factor. 



Tables 16 to 20 give all such matings from the I wild up through the 

 ■jV wild. The summary of all these matings is given in table 21, 

 showing conclusively that black is epistatic to brown, irrespective of 

 whether the male guinea-pig produces brown gametes, as in matings 

 recorded in tables 6, 17, and 18, or whether the female hybrids produce 

 such gametes as in the matings recorded in tables 16, 17, 18, 19, and 20. 

 The total number of young, from such females of 6 different blood- 

 dilutions, is 680 (table 21). In not a single case was there any reversal 

 of dominance, every cross giving black offspring when expected. For 

 instance, in the matings recorded in table 16, 5 females (9 90, 9 91, 

 9 107, 9 115, and 9 124) gave only black young, but they proved their 

 heterozygous nature in matings recorded in table 22 by producing some 

 brown young when mated to a brown male. All heterozygous females 

 and guinea-pig sires in this experiment were similarly tested. 



The result of all these matings is precisely what would be expected 

 of similar matings involving homozygous black in guinea-pigs, as 

 far as the qualitative character of black is concerned; nevertheless, 

 extremely dilute forms of black arose in matings of brindled males to 

 a number of yV ^d hybrid females. These males carried black in a 

 homozygous condition; but, as far as was known, carried no dilution 

 factor. Matings are to be made which will show whether the males 

 really carry such a factor or whether the extreme dilution is but 

 another case of unexpected disturbance or modification in a factor 

 which has been held to be fairly uniform. 



HETEROZYGOUS BLACKS MATED WITH BROWN. 



Retrogressing for a moment, it will be recalled that brown males 

 617, 9246, and NW were mated with some homozygous black | wild 

 females, producing 24 black offspring, presumably heterozygous. To 

 estabUsh a race of brown hybrids, 14 of these J wild offspring were 

 mated to brown males (table 22). The total number of young pro- 



