August S, 1913] 



SCIENCE 



205 



of annual rings at the bases of branches may 

 also have a possible relation to the movements. 

 At any rate, it seems more promising to seek 

 for some anatomical differences between the 

 upper and under sides of branches as the 

 cause of the movement than to study their 

 water content. 



J. G. Grossenbaoher 

 Bureau of Plant Industry, 

 Washington, D. C. 



SPECIAL ARTICLES 



" YELLOW " AND " AGOUTI " FACTORS IN MICE 



Some time ago Mr. A. H. Sturtevant^ sug- 

 gested the hypothesis that there is negative 

 coupling between the " yellow " and the 

 " agouti " factors in mice. At that time" I 

 offered certain facts which appeared to me to 

 give evidence contradictory to the hypothesis 

 which he advanced. 



I included in this evidence the data offered 

 by certain matings of mice made by Miss F. 

 M. Durham." It now appears that I misunder- 

 stood the true meaning of her tables, which 

 were somewhat ambiguous, and that accord- 

 ingly the only remaining evidence which I pos- 

 sessed against Mr. Sturtevant's hypothesis was 

 afforded by the results of certain matings 

 which I made about five years ago. 



It seemed, therefore, advisable to make 

 crosses calculated to test his hypothesis with 

 the stock which I have at present on hand. 



The first of these matings was between wild 



agouti mice and yellow mice which did not 



carry the agouti factor. To use Sturtevant's 



terminology these individuals were as follows : 



Yellows— r< yt, 



Agouti— 3/r yT. 



Two sorts of individuals, yellow and agouti, are 

 expected in equal numbers from such matings. 

 The actual results were 14 yellow, 28 agouti. 

 The yellows should on Sturtevant's hypothesis 

 be of the formula Yt yT and form only two 



»Sturtevant, A. H. (1912), Am. Nat., Yol. 46, 

 pp. 368-371. 



^Little, C. C. (1912), Am. Nat., Vol. 46, pp. 

 491-493. 



"Durham, F. M. (1911), Jcmrnal of Genetics, 

 Vol. 1, pp. 159-178. 



sorts of gametes Yt and yT. Such yellows 

 should by any non-yellow animal, or when 

 mated inter se, give only two sorts of young, 

 yellow and agouti. Actually they produced 23 

 yellow and 18 agouti young. 



Thinking that possibly the hlach factor 

 might be necessary to obtain such a result, I 

 mated three homozygous dilute brown agouti 

 animals with a single brown-eyed yellow 

 (carrying no agouti). All these animals lack 

 the factor for black. The first generation gave 

 11 yellows and 5 brown-agoutis. The yellows 

 were then crossed with dilute hrown animals 

 which did not possess the factor for agouti. If 

 according to Sturtevant's hypothesis there was 

 negative coupling or repulsion between the yel- 

 low and agouti factors there would be only 

 yellow and agouti young from such a mating. 

 If, on the other hand, these factors were en- 

 tirely independent we should have non-agouti 

 young as well. The results follow. 



The conclusion is obvious that the factors 

 for yellow and agouti are unable to go into the 

 same gamete. On the other hand, the factors 

 for " density " and " dilution " of pigmenta- 

 tion show no such relation to any other factors. 



Since I have no reason to doubt the authen- 

 ticity of the contradictory cases, in my own 

 work, to which I have already referred, it 

 seems probable that the factors for "yellow" 

 and " agouti " are not absolutely incompatible, 

 but that they may in rare cases occur in the 

 same gamete. As a general thing, however, it 

 seems that Sturtevant's hypothesis is correct 

 and that a negative association exists between 

 these two factors. 



C. C. Little 



BussET Institution, 

 Foeest Hills, Mass., 

 July 7, 1913 



