250 EVOLUTION, GENETICS, AND EUGENICS 



ancestor, the wild rock dove; in other words, reversions occur. Often, 

 however, the results seem quite anomalous, which is probably due to 

 the number of latent characters which different races of pigeons appear 

 to carry. 



Mice. — Mendelian phenomena have been carefully studied in 

 mice. Thus, when a grey mouse is paired with an albino, the hybrid 

 offspring are always grey. When these are inbred, they yield greys 

 and albinos, approximately in the proportion of 3:1. Thus Cuenot 

 obtained 198 grey, and 72 albinos. 



Darbishire has obtained many results which harmonise well with 

 Mendelian theory, while others require some ingenuity if they are to 

 be fitted in with this interpretation. As a good case we may cite one 

 where the inbreeding of pigmented mice — derived from crossing pig- 

 mented and albino individuals — yielded 159 pigmented young and 55 

 albinos (53.5 being the theoretical anticipation). When similar 

 hybrids were paired with pure albinos, they yielded 69 pigmented and 

 69 albino forms, precisely as the theory would lead us to expect: 



D R 



D(R) 



X 

 D(R) 



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+2 D(R)+i R 

 X 



D(R) R 



Culnot crossed an albino AG (with latent grey) with an albino AB 

 (with latent black), and obtained albinos (AGAB). He crossed a 

 black mouse CB with an albino AY (with latent yellow), and obtained 

 yellow mice (CBAY). He then paired AGAB (albino) with CBAY 

 (yellow) and obtained 151 young — 81 albinos, 34 yellow, 20 black, 16 

 grey; the theoretical anticipation being — 76 albinos, 38 yellow, 19 

 black, 19 grey. This is an exceedingly striking and convincing case. 

 Waltzing mice. — The mice of this interesting Japanese breed have 

 among other peculiarities the habit of waltzing round in circles. When 

 waltzing mice are crossed with normal mice, their abnormal quality 

 behaves as a recessive. 



