DEPARTMENT OF GENETICS.^ 



C. B. Davenport, Director. 



GENERAL STATEMENT. 



In its second year following reorganization the work of this Department 

 has shown itself especially productive, justifying the hopes we have had that 

 the combination of research in plants, animals, and man would be a fruitful 

 one. Despite the large extent of subjects covered, all investigations fall 

 under the one subject of inquiry: the gametic constitution, its mechanism, 

 its combinations, and their somatic manifestations. 



While all investigations have been unusually prolific, three are sufficiently 

 outstanding to warrant special mention. These are, first, the experimental 

 modification of the germinal constitution in mice; second, the rapid opening 

 up of the phenomenon of aberrations in the chromosome-complex of Datura 

 and the mutations that result therefrom; and third, new light on the control 

 of sex and the sex-ratio. 



As modern genetics has been bringing to light the dependence of somatic 

 form and structure on the architecture and number of chromosomes, the 

 urgency of the problem of the experimental control of the structure and num- 

 ber of chromosomes has become more pressing. Indeed, not until such con- 

 trol is secured may the era of experimental evolution strictly be said to have 

 been entered upon. While attempts to modify the germ-plasm may have 

 been more or less successfully made by Stockard and McDowell with alcohol, 

 by Guyer with cytolysins, and by others, yet none of these have yielded a 

 type of inheritance that lent itself to Mendelian analysis. In this respect 

 the results obtained by Dr. Little, with the cooperation of Dr. H. J. Bagg, 

 are much more clean cut. By subjecting mice to X-rays some grandchildren 

 were obtained with abnormal eyes. These were then bred from and sub- 

 jected to the ordinary genetical analysis. Apparently a single-gene mutation 

 affecting the eye has been induced, and this reappears in subsequent untreated 

 generations like a Mendelian recessive. Moreover, in one or more chromo- 

 somes other genes have apparently been set mutating so that abnormal heads, 

 appendages, trunk, and epidermal organs are appearing. Inasmuch as the 

 control of mutation is the experimental control of evolution, outside of and 

 beyond the ordinary operations of hybridization, the possibilities of such 

 experimental control (now in its infancy) can not be overestimated. 



The second outstanding result is the further analysis of the variations of the 

 chromosomal complexes and their corresponding somatic mutation. Varia- 

 tions in the number of chromosomes had, indeed, been seen by others; that 

 "non-disjunction" was accompanied by somatic modifications had been 

 shown by Bridges in Drosophila; but it has remained for Datura to reveal in 

 the hands of Blakeslee and his associates, Belling, Farnham and others, an 

 extensive system of inter-chromosomal mutation and corresponding somatic 

 change the like of which had been entirely unknown. 



The studies of Morgan, Sturtevant, Bridges, and Muller of gene mutation 

 and of Blakeslee and his associates on holochromosomal mutation, as well as 



'Situated at Cold Spring Harbor, Long Island, New York. 



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