38 GENETIC STUDIES ON A CAVY SPECIES CROSS. 



is a ratio of 89 : 30 or 90 : 29. The excess is between 9 and 10 indi- 

 viduals. Nevertheless, it is interesting to note that there was an excess 

 of dominants in the ratios obtained by mating heterozygotes to albinos 

 (table 50) ; hence the excess of recessives in one case offsets the excess 

 of dominants observed in the other. 



ALBINOS MATED INTER SE. 



No matings were made of albinos with albinos. It is safe to assume 

 that the albino hybrids would breed true and agree with the guinea- 

 pigs in this class of matings, as they do in all other classes of matings. 

 The very fact that a hybrid which is heterozygous in the color factor 

 can form pure gametes of two kinds would be strong argument that 

 albinos breed true. Extracted recessive albino hybrids in previous 

 tables have given no evidence of producing gametes with the color 

 factor when they were mated to guinea-pig males heterozygous in color. ^ 



8., ROUGHNESS AND SMOOTHNESS. 

 HOMOZYGOUS ROUGH ANIMALS IN CROSSES. 



It has been often stated that domestic varieties are commonly 

 derived from the wild by the loss of one or more factors; hence the 

 wild is the dominant form, since the presence of a factor is epistatic to 

 its absence. The rough coat of the domestic guinea-pig seems to be 

 an exception to this apparently rather general rule, for the rough 

 character is not found in any wild cavies, yet it is a progressive domi- 

 nant variation. The rough or rosetted condition of the coat in guinea- 

 pigs is subject to much variation, but whenever a homozygous rough 

 animal is mated to a smooth one all the offspring show the rough 

 character, and by mating the Fi generation inter se the smooth form 

 can be extracted in the Fs generation. The number of experiments 

 on the wild hybrids which involve the rough coat character are few; 

 nevertheless the numbers are large enough to be significant, particu- 

 larly since the inheritance of this character in guinea-pigs has been 

 shown to be Mendelian. 



Two homozygous rough male guinea-pigs were mated to three female 

 hybrids (table 56) and yielded 10 rough offspring. Two of the females 

 used as dams were smooth, | wild hybrids, and the other was a hetero- 

 zygous, rough, ^V wild hybrid. The total number of 10 rough young 

 would be far too small to serve as a basis for any generalizations, if we 

 did not have reason to suspect that the hybrid and guinea-pig transmit 

 the same characters in a similar manner. Since we know this to be a 

 fact for the other characters whic h we have already considered, the 



'Since this statement was written fertile male albino hybrids have been mated to female 

 albino hybrids and have produced only albino young. 



