474 



The Journal of Heredity 



^hc dilution of mice and may well be 

 put in the same class. 



ALBINO SliRIKS OF ALLELOMORPHS 



The Mimala\'an rabbits resemble albi- 

 nos except that they show a brownish- 

 black color at the jDoints. They never 

 show yellow under any conditions. Per- 

 fect albinos are also well known in 

 rabbits and Castle' found that each of 

 these t\-pes sej^rej.,^ited from crosses with 

 fully colored rabbits without producini; 

 the other and, in crosses with each other, 

 also followed unit Mendelian inherit- 

 ance. He concluded that the Hima- 

 layans contain a modification of the 

 color factor. The series of three varia- 

 tions aj^'rees well with the series of 

 four in <^'uinea-i)if^s and of three in rats. 

 It is interestinjj; to note, howe\-er, that 

 the lowest known albino allelomorph in 

 j:!;uinea-piji:s seems to correspond rather 

 with the Himalayan than with the 

 perfect albino in rabbits. 



AGOUTI SKRIKS OF A LLKLOMORPHS 



As in other rodents, black was early 

 found to be a simple recessive to fj;ray.'' 

 An intermediate condition is known in 

 the black-and-tans in which the back 

 is black with only a few ticked hairs 

 while the belly is white and yellow. 

 This was shown by Castle and Fish" to 

 be due to an intermediate variation of 

 the same factor b)- which ^rays differ 

 from blacks. This series of three allelo- 

 mor])hs is naturally to be compared 

 with Cuenot's series of four in mice: 

 jellow, li^'ht-bellied k'ray, j^ray-bellied 

 gray and black. The scqviencc of 

 effects seems different but such a 

 difference m.ay well be due to independ- 

 ent causes. It may be pointed out that 

 in a stock of mice with a hij^^her density 

 of black than usual (due to factors of 

 class 2a3) the sequence of effects ])ro- 



duced l)y the four ai^'outi allelomorphs 

 ajjproaches that in rabbits. 



DENSITY SERIES OF ALLELOMORPHS 



The series of three allelomorphs for 

 density of black or brown (Ed , E and 

 Ey ) is a very interesting one. Castle^ 

 demonstrated that sooty yellow (black 

 belly and tail) and clear \-ellow (white 

 belly and tail) differ from black and 

 gray rabbits res])ectively by the .'^ame 

 recessive Mendelian factor. He called 

 the contrasted characters extension and 

 restriction of black. Punnctt** discov- 

 ered a new dominant factor in the 

 presence of which rabbits which would 

 otherwise be gray were black. This 

 factor, of course, produced no visible 

 effect in animals which were already 

 black. He called this the density 

 factor. He found it to be inherited 

 independently of the agouti series but 

 completely coupled with the extension 

 factor E. The numerical results of 

 complete coupling are identical with 

 those of multiple allelomorjihs. The 

 two terms are useful only in theory. 

 Factors which are partially coupled have 

 no necessary physiological relationship 

 as has been abundantly shown in 

 Morgan's work on Drosophila. But the 

 nmnerous cases of multiple allelomorphs 

 or complete coupling in mammals 

 apparently all involve physiological 

 relationship.'-* The factors when ar- 

 ranged in the order of dominance 

 detemiine a linear series of physiological 

 effects. Again, even partial coupling 

 seems to be relatively uncommon in 

 mammals owing presumably to the 

 large number of chromosomes. But at 

 least nine .series of multiple allelomorphs 

 are known among them. The main 

 effects of Punnett's density factor fit 

 admirably into the extension, or ])erhaps 

 better, densitv series in rabbits. With 



* Castle, W. E. l^O.S. Caru. lusl. Wash. I'lih. No. 23, 78 pp, and Castle and associates, 

 1909, ibid. 



^ Hurst, C. C. 1905. Lof. cit. 



•Castle, W. K. and Fish, H. D. 1915. Amer. Nat., 49:88-96. 



' Castle, W. K. and associates. 1909. Loc. cit. 



« Punnctt, R. C. 1912. Jour. Gen., 2:21; 1915, Jour. Gen.. 5;.U-50. 



'This distinction between complete couplinj^ and multii)lc allelomoriihs was pointed out 

 clearly by Sturtevant in connection with alt)ino series in rabljits, 1913. Amer. Nat., 47:234-238. 

 In the case of the density scries discu.ssed here, interpretation as a series of multiple allelomorphs 

 or "i)olvKamous factors" instead of by complete coupling was suggested by Wilson, 1912, 1913, 

 Set. Pr'oe. R. Puh. Sac. 



