ALLEN. — THK HKRKDITY OF COAT COLOR IN MICE. 99 



(Iieni having complete albinism recessive, while the other half arc heter- 

 ozygous with respect to total aud partial pigmentation. If these young 

 he now intercrossed in all possible ways, the final result will be that only 

 1 in IG individuals will be albino, instead of 1 in 4. To make this 

 more clear, the two possible cases are worked out below, D representing 

 the dominant condition of total pigmentation as seen in the wild house 

 mouse or rat ; DR, the mosaic or spotted condition in which albinism 

 occurs ill the soma between pigmented patches ; aud R representing the 

 albino condition. A period between two of these signs used together 

 shows that segregation takes place at that point and the resulting gametes 

 are of the nature expressed by the symbols ou the right and the left of 

 the period respectively. 



Case I. 



Heterozygote = DR-R; homozygote = D-D. This mating gives the 

 following result : 



DR + R = gametes of heterozygote, 



D + D = " " homozygote, 



2D-DR + 2D"R=:i offspring, or generation Fj. 



If, now, these Fi animals be allowed to breed inter se, three com- 

 binations (a., b., c.) are possible, and the smallest number of individuals 

 representing all the possible unions in their probable proportions is 

 16, thus : 



a. b. 



Parents both D-DR Parents both D-R 



D -f- DR D + R 



D + DR D + R 



D-F2DDR+DR D + 2DR-f-R 



c. 

 Parents one DDR, the other DR 

 D-t-DR 



D + R 



2(D + DDR + DR 4- DRR) 



There is one chance each for mating a and h, where there arc two 

 chances for mating c. If all these unions take place in tlieir chance 

 frequencies, there will result six sorts of animals as follows : 



