ALLEN. — THE OEREDITY OF COAT COLOR IN MICE. 



Ill 



All white : .... 

 7 white : 1 pigmented 

 G white : 2 pigmented 

 5 white: 3 pigmented 

 4 wliite : 4 pigmented 

 3 white: 5 pigmented 

 2 white : G pigmented 

 1 white : 7 pigmented 



All pigmented . . . 



1 chance in 12,870 



64 chances in 12,870 



784 chances in 12,870 



3136 chances in 12,870 



4900 chances in 12,870 



3136 chances in 12,870 



784 chances in 12,870 



64 chances in 12,870 



1 chance in 12,870 



The experimental results obtained indicate, therefore, that the pro- 

 duction on the average of an equal number of gametes of both sorts 

 actually takes place, although sejiarate litters are quite as apt to exhibit 

 a discordant ratio as the theoretical one. 



A ratio of 1 albino to 15 pigmented animals is to be expected in cases 

 where the Fi individuals are interbred at random, the one parent being 

 heterozygous with respect to albinism and either total or partial pig- 

 mentation, the other parent having that one only of the last two coat- 

 characters which is not possessed by the heterozygote ; where, in other 

 words, three different allelomorphic characters are brought to the union, 

 and the Fi generation consists of two classes of young, one of which 

 still contains albinism as a recessive character, while the other contains 

 only the two pigment allelomorphs. Generation Fo, obtained by inter- 

 breeding at random the young of Fi, should contain six classes of 

 individuals. The actual occurrence of some of these classes has been 

 experimentally demonstrated. 



A third possible combination, in which one parent is heterozygous with 

 respect to one pigment character and albinism, and the other is heterozy- 

 gous with respect to two pigment characters, is theoretically capable of 

 producing four sorts of individuals in F^, none of w'hich is unpigmeuted. 

 The actual occurrence of such a result is indicated by the present series 

 of experiments. 



Complete albinism, so far as certainly known, is a recessive character 

 in the Meudelian sense, when brought into competition with a pigment 

 character. Two pure albinos when mated, produce albinos only, so far 

 as at present tested, but it must not from that be assumed that any two 

 albinos are physiologically equivalent as regards their influence on the 

 heredity of pigment characters, in crosses with pigmented animals. 



