Wright : Color Inheritance in Mammals 



141 



more discrepancies among females than 

 among males. He finds 22 exceptions 

 among 263 female kittens, or 8.4%, 

 but only 3 among 294 males, or 1.0%. 

 A color which depends on a sex-linked 

 factor is inherited by males wholly 

 from their mothers. Thus black fe- 

 males (EE) should have only black 

 sons (E-), yellow females (ee) only 

 yellow sons (e-), and tortoiseshell fe- 

 males (Ee) both blacks (E-) and yel- 

 lows (e-) in equal numbers, regardless 

 of the colors of the sires. The data 

 fit the theory admirably among the 

 294 males except for the occurance of 

 3 tortoiseshells. Cutler and Doncaster-^ 

 have recently presented evidence in- 

 dicating that tortoiseshell males are 

 generally sterile. This makes it prob- 

 able that something more is involved 

 than the action of subsidiary extension 

 factors, and the authors suggest that 

 there may be a connection between the 

 sterility and the possession of a color 

 normally belonging to the female. Put- 

 ting this suggestion in a definite form, 

 it may be taken to mean that the rare 

 tortoiseshell males may be cats with 

 the two X chromosomes of females, 

 but in which some other cause has 

 overbalanced the sex-determining ten- 

 dency of the X chromosomes, and pro- 

 duced males or near males. Such an 

 interpretation would fit well with the 

 results of Whitman and Riddle^- in 

 sex control in pigeons, and with Gold- 

 Schmidts'^^ work on sex-intergrades in 

 Gypsy moths. 



The absence of other discrepancies 

 among the males shows that very few 

 if any of their mothers could have dif- 

 fered in color from that expected on 

 their genetic constitution. But these 

 same mothers produced 8.4% aberrant 

 daughters which in the next generation 

 would be expected to produce many 

 aberrant sons. More experiments under 

 laboratory conditions are needed. Al- 

 most any records should give reliable 

 results for males since there should 

 never be any question about the iden- 

 tity of the mother of a kitten, but for 

 females, the sire must be known as 

 certainly as the dam and certainty as 

 to the sire is notoriously difficult to 

 establish in cats. 



The effects of the factor, which change 

 black to tortoise or orange, place it on 

 the whole in class 2a2, with the factors 

 for tortoise and self yellow in guinea- 

 pigs. As has been noted before, how- 

 ever, the distinction between classes 2a2 

 and 2a3, i.e., factors which determine a 

 patchwork of black and yellow and 

 those which determine a uniform change 

 in the density of black, is not very 

 sharp. In a few tortoise-shell kittens, 

 which the writer has observ^ed, the 

 black parts of the coat have a brownish 

 hue and appear much less intense than 

 the black of solid black kittens of the 

 same litters. This indicates that, in 

 cats of formula of Ee, there is a general 

 reduction in density of black which 

 easily passes into complete elimination 

 in irregular spots in the coat. This 

 leads to comparison with the sooty yel- 

 low or tortoiseshell rabbits which have 

 even more claim to be put in class 2a3. 



THE PATTERN OF TABBY CATS 



The common tabby cat has a very 

 complex pattern with an obvious rela- 

 tionship to the color patterns of wild 

 Felidae, and these are of a general type 

 which is very common among other wild 

 mammals. vSeveral kinds of variations 

 are found in domestic cats and a study of 

 these is of great interest for the light it 

 throws on the colors of mammals in 

 nature. In the common tabbies wdth 

 the tiger pattern, there are alternate 

 dark and light stripes running perpendi- 

 cularly down the sides of the body, longi- 

 tudinally along the back and head, and 

 around the legs and tail. The dark 

 stripes are usually of hair which is wholly 

 black w^hile each" hair in the light stripes 

 is black with a cream colored band near 

 the tip, thus resembling the hair of 

 agouti-colored rodents. The colors on 

 the back are more intense than those on 

 the belly. The variations in the tabby 

 pattern "^ have been studied in much 

 detail bv Dr. Whiting to wdiom the 

 writer is indebted for permission to use 

 genetic results on which the following 

 discussion is based. 



The two elements in the tabb\- pat- 

 tern, i.e., the striping of the coat as a 

 whole, and the banding of individual 

 hairs, varv wholly independently of 



