376 



The Journal of Heredity 



vv Vv vv 



SS self slightly pied not born 



Ss nearly self pied not born 



SS pied black-eyed white not born 



(or nearly so) 



It seems questionable whether this 

 should be called a dominant white. 

 It cannot, of course, be determined 

 whether the heterozygote Vv is closer 

 to the unknown homozygote VV than 

 to self vv, but it may be pointed out 

 that the ordinary piebald factor would 

 be considered dominant if the homozy- 

 gote ss were not known, as would also 

 be the case in Dutch rabbits and 

 hooded rats. In man a white blaze is 

 generally considered to be due to a 

 dominant factor, but as no cases have 

 been reported in which homozygotes 

 would be expected to appear, it is not 

 at all unlikely that it is no more domi- 

 nant than the piebalds in rodents. In 

 any event, the two piebald factors mvist 

 be classified together. Both of them 

 affect color in general and must be 

 considered as acting on enzyme I of 

 the previous paper. Further they must 

 be considered as doing this through 

 influence on a common develo])mcnlal 

 factor Vjack of enzyme 1. If their 

 modes of influence on enzyme 1 were 

 wholly independent of each other in 

 development, we would expect one 

 pattern to be simply laid over the other 

 as in white patterns often foimd in roan 

 Shorthorn cattle, or in the relations of 

 piebald in mice with the white belly of 

 many light-ljcllied agouti mice. But 

 in the combination ssVv it is the 

 quantity of white, not the pattern, 

 which is comliined. 



No doubt there are other factors with 

 smaller effects than these two which are 

 inherited independently but co6])erate 

 in develoj^ment. Little"^ describes wild 

 mice with the formula of self SSvv, 

 which yet had a white blaze. The 

 mode of inheritance was irregular al- 

 though there were distinct indications 

 of segregation. 



The dilution of blue mice was demon- 

 strated to be due to a recessive factor 



by Miss Durham. ^^ Little^ confirmed 

 this result and showed that there is 

 another kind of dilution in mice which 

 pnxluces even more striking effects in 

 yellows and is inherited independently. 

 It seems to follow practically a mode of 

 blending inheritance which has not 

 yet been analyzed as Mendelian. Ac- 

 cording to Little, factor i reduces black 

 to blue, and red to a peculiar washed- 

 out light red, while the second type of 

 dilution has no appreciable effect on 

 black, but reduces red to a cream in 

 which the hue is different from light 

 red. Factor i evidently belongs in 

 class las. It is very different from 

 the dilution of sepia guinea-pigs and 

 has been shown by Miss Durham to be 

 transmitted independently of albinism. 

 The cream type of dilution docs not 

 seem to fall into any of the classes given 

 as no provision is made for dilution of 

 yellow without coordinate dilution of 

 black. However, it is characteristic of 

 the dilution of class lb that much 

 greater effect is produced on yellow than 

 on black. Thus in dilute guinea-pigs 

 (CdCd) the yellow parts of the fur are 

 markedly paler than the red of intense 

 ones (CC) yet the black ])arts are 

 hardly distinguishal^le. It is only in 

 the lower combinations of the albino 

 allelomorphs in guinea-pigs such as 

 CdCa, the heterozygote between dilute 

 and albino, that marked dilution of 

 black becomes apparent. Thus luian- 

 alyzed dilution of mice must be placed 

 in class lb and can be comjiarcel with 

 the unanalyzed minor variations in 

 intensity in guinea-pigs which coojK'rate 

 with the albino series. 



Complete albinism of mice was the 

 first Mendelian factor to be demon- 

 strated in mammals. Cuenot's-' result 

 has been confirmed by all later workers. 

 In rats, guinea-i)igs and rabbits varia- 

 tions have been discovered which are 

 intermediate between full color and 

 albinism and in all three it is clear that 

 albinism is the extreme in a dilution 

 series and is wholly independent of the 



'" Little, C. C. 1914. Amcr. Nal., 48:74-82. 



'» Durham, F. M. 1908. Loc. fit. 



2" Little, C. C. 1911. Sci. N. S., .S3: 896-897. 



»' Cu(:-not, L. 1902. Arch. Zool. Exp. el Gen., (3), 10. 



Notes et revue, p. 27, 



