92 



WRIGHT 



alternate orange and cream stripes 

 which on our interpretation must indi- 

 cate alternate stripes of high and low 

 potency of enzyme I. In tabby cats, the 

 intense stripes are solid black, the pale 

 stripes show yellow ticking which 

 seems to require that enzyme II also 

 be strong in the former, weak in the 

 latter. 



CONCLUSION 



In the present paper an attempt has 

 been made to relate the findings of the 

 biochemist in regard to melanin pig- 

 ment with the great mass of curious 

 relations between colors which have 

 come to light in genetic work. A 

 scheme is given which is designed to 

 show the inter-relations of the differ- 

 ent mammalian coat colors and a clas- 

 sification of color factors is suggested. 

 It is hoped that these will be of use in 

 organizing our present very extensive 

 knowledge of color inheritance and in 

 aiding in the discovery of new facts, 

 or at least in leading to a better scheme 



and classification. 



Finally the bringing under one point 

 of view of biochemical and genetic 

 facts would have great intrinsic inter- 

 est. The present paper attempts merely 

 to trace the character— coat color- 

 back one stage in development. Instead 

 of considering factors as acting on this 

 one character, they have been divided 

 into two sets acting on two characters, 

 production of the hypothetical en- 

 zymes I and II. Suggestions have been 

 made in certain cases in regard to fur- 

 ther tracing back of the action of the 

 factors. A more thorough comparison 

 than has yet been made of the effects 

 of factors in all combinations should 

 yield much data bearing on the process 

 of pigmentation and give a very much 

 more complete understanding of the 

 heredity of color than we have at 

 present. By constant comparison of 

 the deductions from such work with 

 the findings of the biochemist, it 

 should be possible in the end to estab- 

 lish a very pretty correlation of results. 



W 



Unit Character Variation in Rodents 



L. C. DUNN 



Reprinted by author's and publisher's permission 

 from Journal of Mammalogy, vol. 2, 1921, pp. 

 125-140. 



By the time this paper by Dimn was written, it had become ap- 

 parent that many of the visible variations that occurred in laboratory 

 animals could be accoimted for by assuming the existence of minute 

 variatiojis in their hereditary materials. These germi?ial variations, 

 called mutations, became an important part of the Darwinian theory 

 of evolution, after a period during which they were thought to 



