Seftekbeb 3, 1909] 



SCIENCE 



313 



We are indebted to Dr. Alexis Carrel, of the 

 Eockefeller Institute, for valuable suggestions 

 as to operative technique, and to the Carnegie 

 Institution of Washington for material assist- 

 ance through a grant to the senior author. 

 W. E. Castle, 

 John O. Phillips 

 FoBEST Htt.t.s, Boston, Mass., 

 August 11, 1909 



THE PECUUAR INHERITAKCE OF PINK EYES AMONG 

 COLORED MICE^ 



Eeaders of Science are well acquainted with 

 the fact that color-inheritance in mice pre- 

 sents many difficult problems. To one of these 

 problems we are hopeful that we have found a 

 solution. Mice occur in the same fundamental 

 color-varieties as guinea-pigs, most of which 

 are found also among rabbits." These color 

 varieties occur in two series, one the usual or 

 intense series, the other a dilute or pale series. 

 Bateson (1909) considers the pale series a 

 quantitative modification merely of the in- 

 tense series, but there are some reasons for 

 regarding it as a qualitative modification. 

 But whichever it may prove to be, the dilution 

 is demonstrably interchangeable from one color 

 variety to another, so that it may conveniently 

 be treated as due to an independent factor. 



Mice are peculiar in that they possess 

 another series of color varieties, or really two 

 other series, as we shall try to show, not found 

 in mammals generally. 



In this series the eye is apparently pink, 

 but in reality, as Miss Durham has shown, 

 it is very slightly black or brown pigmented. 

 Further, black or brown pigments of the coat, 

 if present, are pale in pink -eyed mice. 



We find, however, that the paleness of the 

 pigments in such cases is not commonly due 

 to the same factor as the paleness of coat in 

 the dilute series having dark eyes, but to a 

 different factor which may or may not be as- 

 sociated with the dilution factor and which 

 we regard as a quantitative modification of the 



' Contributions from the Laboratory of Genetics, 

 Bussey Institution, Harvard Universit) , No. 2. 



' See Science, January 25, 1907 ; August 30, 

 1907; August 21, 1908. 



pigmentation, while the dilution may be re- 

 garded as a qualitative modification of it. 



We recognize, accordingly, four series of 

 color varieties among mice, two dark-eyed and 

 two pink-eyed. Dark-eyed and pink-eyed 

 may each occur in an intense series and 

 in a dilute series. The reason that they 

 have not been recognized sooner is that 

 the intense pink-eyed animal is really less 

 heavily pigmented than the dilute dark-eyed 

 animal of the same color-type, and so all pink- 

 eyed animals have been considered dilute. 

 But that such is not the case is shown by the 

 following experiment. If a pink-eyed gray 

 (intense) animal is mated with a dark-eyed 

 pale cinnamon (dilute) the young are all both 

 dark-eyed and intense; namely, the color of 

 wild house-mice (gray). 



Now if such grays are bred together they 

 produce: (1) grays (both intense and dark- 

 eyed) ; (2) blue-grays (dilute and dark-eyed) ; 

 (3) pink-eyed grays (intense but with reduced 

 amount of pigment), and (4) pink-eyed pale- 

 grays (dilute and with reduced amount of 

 pigment). Manifestly this is a case of Men- 

 delian dihybridism, in which the pigmentation 

 has been modified in two different ways. Each 

 modification affects the fundamental color- 

 factor, C, and may be transmitted through 

 albinos, or from one color variety to another. 

 For convenience of reference we place in a 

 table the names of the four series of color- 

 varieties which we recognize. Most of these 

 have already been identified but there is still 

 uncertainty about a few of them. In the table 

 p. means pink-eyed as well as " paucity " of 

 black or brown pigment in the coat. 



The albinos being wholly unpigmented are 

 indistinguishable in the several series except 

 by breeding tests. 



A specific experiment illustrative of the fore- 

 going account, though involving a greater 

 number of factors, is the following. 



' The coat looks to the unaided eye very similar 

 to that of the dark-eyed pale cinnamon. 



* This variety has a coat much less heavily pig- 

 mented than the dark-eyed blue, but if crossed 

 with cream it produces black and gray young, 

 not blue and blue-gray. 



