LINKAGE IN GAMMARUS CHEVREUXL 



By J. S. HUXLEY, 



Neiij CuUege, Oa-ford. 



The work of Allen and Sexton ('17) shcjwed that Mendelian inherit- 

 ance occurred in Gavirnaras chevreaxi. Three mutations in eye-colour 

 appeared and proved to be due to recessive changes in three Mendelian 

 genes. These factors may be designated respectively B (black) and h (red); 

 (J (colour) and c (absence of colour) ; and W (white) and w (no-white). 

 However, some of the ratios obtained from crosses where two or three 

 factor-pairs were involved departed considerably from expectation. It 

 seemed that they might be due to linkage of factors B and C. This 

 hypothesis could not be tested from the data in Allen and Sexton's 

 paper, since the make-up of the heterozygotes involved was not recorded. 

 Accordingly it was decided to test for linkage by breeding. Through 

 the kindness of Mrs Sexton, I was provided with a number of almost 



(B G W\ 

 ' ' j and 



' ' ^ ] with triple recessives 



I — ^ — ) . Unfortunately, only a very few triple recessives were available, 



so that the more desirable back-cross could not be undertaken at once. 

 A number of broods, however, have been raised from the triple hetero- 

 zygotes mated mter se, and figures obtained which warrant the assertion 

 that linkage exists between B and C. I have therefore thought it best 

 to publish at once the data on which this assertion is based, while con- 

 tinuing and amplifying the experiments in various directions. 



If no linkage exists among the factors and no differential viability 

 among the classes of offspring, the mating I have mentioned should give 

 the following classes and proportions of offspring in F^ : 



Black, B, C,W 27 



Red, h, C, W 9 



Albino, JS (6), f, W 12 



Black, No- white, B, C, iv ... 9 



Red, No- white, b, C, w ... 3 



Colourless, B (b), c, w ... 4 



Total , 64 



