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PROCEEDINGS OF THE AMERICAN ACADEMY. 



Cuenot ( : 02) also tested the pigmented mice of generation Fo which 

 he obtained by breeding inter se the heterozygotes of generation Fj. 

 This he did by simply interbreeding these pigmented animals. In this 

 case, according to the Mendelian formulae, three sorts of unions are 

 possible: (1) D X D, (2) D X D(R), and (3) D(R) x D(R). From the 

 first two combinations no albinos will be produced ; from the third, there 

 should be produced 25 per cent albinos. Cuenot found these expectations 

 realized, for of a number of the pigmented mice selected at random, about 

 one-half produced only pigmented young (189), and the other half pro- 

 duced the expected 25 per cent of albinos, the actual numbers being 162 

 pigmented : 57 albinos, or 26 per cent albinos. In case of the mice 

 whose union produced no albinos, either one or both animals of each pair 

 must have been of the D class. If one-half were of the D class and the 

 other half of the D(R) class, the precise Mendelian expectation would be 

 realized. Since at least one-half of all the pigmented mice were certainly 

 known to be D(R) because they produced albinos, it is probable that, in 

 those unions which produced no albinos, one at least of the two parents 

 mated was a pure D, the other being probably in some cases heterozygous, 

 in other cases pure. 



The two tables, C and D, show the total numbers of pigmented and of 



TABLE C. 



