GENETIC STUDIES OF RABBITS AND RATS. 25 



size, a majority of the F 2 albinos should have been of small size, 

 averaging less in weight than their colored brothers and sisters. 

 Such was not the case. In the Polish-Flemish cross, 29 out of 113 

 F 2 individuals reared to maturity were albinos. The average adult 

 weight of the albinos was 2,155 grams, that of the entire F 2 population 

 was 2,128 grams. The albinos were actually a little larger than the 

 average, although they inherited their albinism from the small-sized 

 grandparent. Hence no linkage is indicated. In the Himalayan- 

 Flemish cross a similar result was obtained; 11 out of 62 adult F 2 

 individuals were Himalayan albinos. They averaged in weight 2,535 

 grams, the average for the entire population (62) being 2,468 grams, 

 or slightly less. The small size of the Himalayan grandparent did 

 not make the Himalayan individuals any smaller (or even quite as 

 small) as their colored brothers and sisters. Hence no linkage is 

 indicated. 



Yellow color and dilute pigmentation are two recessive unit- 

 characters which were transmitted by the Polish male used in the 

 Polish-Flemish crosses, but were not transmitted by the Flemish 

 animals used in those crosses. This fact affords an opportunity to 

 test the occurrence of linkage between small size and either yellow 

 or dilute pigmentation. 



Three yellow F 2 males averaged in adult weight 2,133 grams. 

 The entire group of 28 F 2 males, of which the 3 yellows formed a part, 1 

 all having descended from the same pair of grandparents, averaged 

 2,156 grams, substantially the same amount. Hence there is no 

 indication of linkage between yellow and small size. 



Fourteen F 2 dilute individuals derived from the mating just men- 

 tioned or from other reciprocal Polish-Flemish matings averaged in 

 weight 2,086 grams, while the average weight of the entire F 2 gener- 

 ation in this cross was 2,126 grams, which is only 40 grams heavier. 

 This difference again is too small to give any probable indication of 

 linkage between dilution and small size. 



Another recessive coat-character, angora (long woolly hair), 

 appeared unexpectedly in the F 2 generation of a cross between a 

 Flemish female (7) and the Polish male (3). A further study of the 

 case showed that the angora character was transmitted by the 

 Flemish parent but not by the Polish. In this case, then, linkage, 

 if found at all, should be found between large size and angora coat; 

 10 adult angoras occurred among the 42 F 2 young reared from this 

 mating. The angoras averaged in weight 2,174 grams; the entire Fj 

 group averaged 2,194 grams, or 20 grams heavier. Clearly, there- 

 fore, angora was not linked with large size. 



1 The reader may wonder why the number of yellow grandchildren was so small. In reality a 

 fourth yellow individual was produced, a female, but she died before attaining adult size. 

 Further, the Polish grandparent transmitted yellow in only half his gametes, so that only part 

 of the Fi individuals inherited the character from him. 



