NOTES AND LITERATURE 



HEREDITY 



F. E. Lutz contributes a very interesting paper 8 in which he 

 presents evidence bearing on the effect of selection in a "pure" 

 strain. Amongst wild flies of this species (Drosophila ampel- 

 ophila) about one third of one per cent, present abnormalities in 

 wing venation. By selection and inbreeding he was able to pro- 

 duce strains with practically 100 per cent, abnormality. In a 

 good many crosses the abnormal venation behaved as a Mendelian 

 recessive in which dominance of normal was not perfect. But 

 in other cases the phenomena observed departed widely from 

 the typical Mendelian behavior. The author suggests that the 

 abnormality is due to a factor which has high fluctuating vari- 

 ability, and that these fluctuations are to a certain extent in- 

 herited. It is shown that Galton's law of ancestral inheritance 

 does not apply to individual families, even when these are large 

 (100 to 200 individuals). 



If we knew the real cause of this abnormality we might pos- 

 sibly be able to reason about its peculiar behavior with some 

 hope of elucidating it. Any attempt at explanation must 

 necessarily be largely hypothetical. The writer would suggest 

 that most of Lutz's data point to the presence of two factors for 

 abnormality, one much stronger than the other, and one or both 

 of them highly variable (fluctuating variability). Davenport 

 found such a case (two factors, one stronger than the other), 

 for the hood in certain fowls. 9 The writer has often thought 

 there ought to be cases of Mendelian factors which just barely 

 give rise to visible expression in the soma. Since all characters 

 exhibit fluctuating variability, such a factor should behave much 

 as the character which Lutz studied. 



Lutz concludes that he has produced effects by selection in ' ' pure 

 lines." This is much to be doubted. The results he secured by 

 selection fit very well the curves shown in my paper on "Some 

 of the Principles of Heredity Applied to Plant Breeding" 10 for 



'"Experiments with Drosophila Ampelophila Concerning Evolution, 

 E. E. Lutz, Carnegie Institution of Wash., 1911. 



*Proc. Wash. Acad. Sci., "Lecture on Heredity," by C. B. Davenport. 

 "Bulletin Bureau of Plant Industry, No. 165. 



