SHOETEE AETICLES AND DISCUSSION 



THE MODIFICATION OF MENDELIAN INHERITANCE 

 BY EXTERNAL CONDITIONS 

 A whole number of the Biological Bulletin (May, 1910) is 

 devoted to Professor "W. L. Tower's article on "The Determina- 

 tion of Dominance and the Modification of Behavior in Alterna- 

 tive (Mendelian) Inheritance by Conditions Surrounding or 

 Incident upon the Germ Cells at Fertilization." The work was 

 done on certain chrysomelid beetles. Lc plinotarsa signal icoll is, 

 L. undecimlineala and L. diversa, all occurring in Mexico. 

 Every biologist who takes any interest in questions of heredity 

 will read this exceedingly important paper, and will be pro- 

 foundly impressed by the data therein presented, but it is pos- 

 sible that he will also be somewhat puzzled. It is in a humble 

 frame of mind that I venture to set forth some of the difficulties, 

 fully realizing that Professor Tower, with his long experience 

 in patiently investigating the chrysomelid beetles, must know 

 what he is about, and that any mere outsider is at a tremendous 

 disadvantage. At the same time, it is after all for the outsider 

 that the paper is written, and it is due to him to make it as clear 

 as possible, and it may be to explain what seem to him insuper- 

 able difficulties. 



L. si-gnat icoll is $ was crossed with diversa J\ giving in F 1 

 about half signaticollis and half a blend between the two. The 

 F x signaticollis mated together gave only signaticollis, and 

 further breeding for five generations gave only the same. The 

 blend, however, split in F 2 into signaticollis, the blend, and 

 diversa, giving the expected Mendelian ratios. (The obvious 

 suggestion here would be that the original male diversa was 

 heterozygous, gametieally identical with the blend.) 



Next, the same cross was again made, using beetles of the same 

 stock but at a reduced temperature. As a result, the F 1 beetles 



repeated eleven times with substantially the same results. 



