276 



SCIENCE. 



[N. S. Vol. XXIV. No. 609. 



low mice, a male (c^ C). A second male was 

 not used in the breeding experiments. The 

 third yellow animal, a female, was sterile by 

 every sort of mating tried, a considerable 

 number, which fact is of interest in connec- 

 tion with Cuenot's experience, to the effect 

 that yellow mice are feeble in reproductive 

 capacity, though vigorous and even savage. 

 (4) The fourth category of mice consisted of 

 a pair of very large albinos and their three 

 young. Subsequent experiments showed that 

 these albinos transmitted as latent characters 

 in their gametes either yellow or chocolate, 

 but in no case black pigmentation. 



Other yellow mice were obtained (1) by 

 mating the yellow male with chocolate fe- 

 males, (2) by mating the albinos mentioned 

 to black animals, and (3) by mating a choco- 

 late female with one of the albinos. 



The experiments which will be described in 

 detail relate to crosses of the yellow mice 

 inter se or with mice of other colors. 



Before passing to a consideration of the 

 crosses, I should mention that the yellow mice 

 obtained in my experiments were of two dis- 

 tinct types in their adult pelage. In their 

 first coat all alike were of a clear yellow color, 

 like the three original yellow mice. This 

 character was retained in a part only of the 

 yellow mice produced in my experiments; the 

 others developed in their adult (second ?) 

 coat a certajn amount of chocolate pigment 

 found associated with the yellow pigment 

 granules, especially toward the base of the 

 hairs. Animals of this second sort I shall 

 call sooty yellow, to distinguish them from 

 the clear yellow type, in the hair of which 

 only yellow pigment is found. Sooty yellow 

 mice are- undoubtedly included in Bateson's 

 (1903) category of ' dingy or sooty fawn ' 

 formed ' when dark pigment is present in as- 

 sociation with predominant yellow.' Cuenot 

 evidently had under observation both clear 

 yellow and sooty yellow animals. He states 

 that the yellow race contains numerous un- 

 fixable variations, not hereditary, ranging 

 from a clear orange yellow to a sooty or gray- 

 ish yellow not very different from the color of 

 gray mice. The statement that these varia- 



tions are not hereditary seems to me unfor- 

 tunate, as seeming to imply that characters 

 are not inherited, unless in conformity with 

 known laws of inheritance. 



The following observations corroborate Cue- 

 not's statement that yellow is a dominant 

 character in mice. Two clear yellow mice 

 (? 3.2* and c? 3.1''), own brother and sister, 

 born of a chocolate female (? 3) mated with 

 the original clear yellow male (c? C), pro- 

 duced, in three successive litters, 8 yellow and 



2 chocolate young. The same female bore, by 

 another clear yellow male, 2 yellow and 1 

 chocolate young. Accordingly her total young 

 by mates of her own color were 10 yellow and 



3 chocolate, a close approximation to the 3 : 1 

 Mendelian ratio. It is clear that chocolate 

 was present as a recessive character in the 

 yellow parents. Black was as certainly not 

 present as a recessive character, since it is 

 known to dominate over chocolate, when pres- 

 ent in the same zygote with it. 



Not all of the yellow young produced by 

 these matings had the same clear yellow color 

 as their parents. Three of them proved to be 

 sooty yellow, on attaining their adult coat; 

 four remained clear yellow, like the parents; 

 and the remaining three died before attaining 

 the second coat, so that they can not be more 

 accurately classified. 



The recessive nature of chocolate in relation 

 to yellow is further indicated by the following 

 matings between a chocolate and a yellow in- 

 dividual, the young being in all cases either 

 chocolate or yellow in color, never black. 



Parents. 



Youns 



Totals, 



16 



23 



The total number of yellows produced in 

 these matings is 21, of chocolates 23. Un- 



