Wright: Color Inheritance in Mammals 



237 



rank in the vertical columns of table 

 4 or 5, making correlation Tables with 

 36 entries. 



The correlation between rank among 

 relatives and rank among husbands and 

 waives is — .51 when the latter are 

 weighted, — .28 when unweighted. The 

 difference seems to be due largely to a 

 smaller degree of nonassortative mating 

 among the grandparents than among the 

 parents. Where the matings are un- 

 weighted the grandparental matings 

 are, of course, more important than the 

 parental. 



TWO KINDS OF DILUTION OF EYE COLOR 



The results as to the connection be- 

 tween the different color varieties agree 

 in the main with those to be expected 

 on any theory. One would expect to 

 find D(D) closer to either D(L) than 

 to L(L), and D(L) closer to D(D) 

 and L(L) than to L(D), whether hair 

 and eyes are inherited independently or 

 in part together. Perhaps the most im- 

 portant point which is brought out is the 

 very low relationship of R(L) to D(L) 

 and the high relationship to L(D). 

 We have seen that there is a physiolo- 

 gical relationship between red hair and 

 light eyes. It seems necessary to sup- 

 pose that the same factor which reduces 

 the amount of black pigment in the 

 hair and permits red to appear in its 

 place, reduces black in the eyes. But 

 we cannot suppose that factors of this 

 class are responsible for the light eyes 

 in black haired persons. Thus as a 

 basis for classifying the color varieties 

 it would seem to be a good working 

 hypothesis to suppose that two funda- 

 mentally different kinds of dilution 

 factors for eye color are at work. One 

 also reduces black hair to red hair ; the 

 other has no such eft'ect. Since, how- 

 ever, both D(L) and R(L) are quite 

 closely related to L(L), we may go a 

 step farther and suppose that the same 

 factors which reduce D(D) to D(L) 

 reduce R(L) to L(L). These relations 

 may be indicated briefly as follows : 

 D(D) R(L) 

 D(L) L(L) 



Let us compare the effects of these 

 hypothetical factors with the classes of 

 color factors found in mammals. A 



factor which reduces red to flaxen or 

 white, in extreme cases, must be placed 

 in class lb with the albino series in the 

 lower mammals. These are factors 

 which are supposed to reduce the 

 amount of the fundamental enzyme for 

 color production ( enzyme I ) . Such 

 factors should produce a dilution of 

 black pigment in hair and eyes as well 

 as of red in the hair, but the dilution 

 should be very much less marked in 

 the black hair. The other class of dilu- 

 tion factors — that which reduces D(D) 

 to R(L) must be placed in 2a3 or 2b. 

 Such factors produce a general reduc- 

 tion in quantity or strength of enzyme 

 II, and leave enzyme I free to develop 

 red pigment. A fairly close parallel can 

 be taken from relations which the 

 writer has found to hold in guinea-pigs. 

 The albino series of four alleomorphs 

 C, Cd, Cr, and Ca may be taken to rep- 

 resent class lb, /. c, general pigment 

 dilution. The pair extension of black 

 (E) and restriction of black (e) of 

 class 2a2 may be taken to illustrate a 

 factor which replaces black by red. 

 The parallel is not complete here, as 

 factors E and e belong to a series in 

 which an intermediate allelomorph Ep 

 produces tortoise shell. The series 

 changes black to red by way of a pat- 

 tern of spots, eyes remaining unaffected, 

 instead of by way of a general dilution 

 wdiich may be expected to affect the 

 eyes. 



The colors called dark and light sepia 

 in guinea-pigs in the earlier papers are 

 here called black and dark brown, the 

 human hair colors which they match. 

 The dark sepia of CdCd, CdCr, and 

 CrCr is, as a rule, sufficiently browner 

 than the black of C — to be dis- 

 tinguishable but is fully as black 

 as the average black hair in Euro- 

 peans. The light sepia of CrCr and 

 CrCa is light only by comparison with 

 dark sepia. Typical samples match 

 very closely human hair which would 

 be called dark brown. It will be seen 

 that the arrangement of hair colors 

 suggested for man is the same for the 

 common colors as that adopted by 

 Davenport, but the theoretical inter- 

 pretation is quite different and brings 

 the eye colors into the same scheme. 



