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THE AMEBIC AN NATURALIST [Vol. XLIX 



THE NON-CONTAMINATION OF GENES 



Eecently the question of the possible contamination of 

 genes (or factors) has been under discussion. Were 

 such contamination possible one might expect to find 

 some evidence of it in a case like this one of abnormal 

 abdomen, if one is justified, at all, in drawing infer- 

 ences from the nature of the character to the nature of the 

 gene that stands for that character. I do not myself 

 think that there is the slightest justification in drawing 

 such conclusions, but let us assume for the moment that 

 such an inference is justifiable in order to examine the 

 bearing of the evidence furnished by this mutant type. 



The heterozygous female carries a factor for normal 

 and one for abnormal. She herself may be either normal 

 or abnormal according to the environment in which she 

 was reared. It might be supposed, since she is abnor- 

 mal, that her normal gene might be more predisposed 

 to contamination by the abnormal gene. The evidence 

 shows that this does not occur ; for, by means of the link- 

 age we can identify the normal flies that should carry the 

 normal, or the abnormal genes, and we find that the re- 

 sults conform completely to expectation ; i. e., they are in 

 full accord with all other linkage results where there is 

 no reason to suppose that contamination takes place. 



Conversely it might be supposed that if the hetero- 

 zygous female were normal in type her abnormal gene 

 might be predisposed to contamination by the normal gene, 

 but again the evidence contradicts the assumption. 



If, on the other hand, it is not supposed that the pheno- 

 typic condition of the female has any part in bringing 

 about contamination (or in serving as an indicator, that 

 conditions are favorable for contamination) but that con- 

 tamination is due merely to juxtaposition of genes in the 

 same cell, then in refutation of the contamination of genes 

 I may cite the evidence cited above, whore in several suc- 

 cessive generations the breeding took place from hetero- 

 zygous females bred to recessive males and the gametic 



