126 GENETICS AND EUGENICS 



other parts of the body retains its full force; whereas in an 

 albino the action of the color factor is everywhere wanting or 

 greatly weakened. 



The variation, ''white spotting," may be regarded as a 

 unit-character change from a condition of uniform action of 

 the color factor to a condition of locally suppressed action of 

 the color factor. The former may be designated S, the 

 latter s. Its inheritance is as sharply Mendelian as that of 

 any other color variation but, the precise extent to which 

 color development is suppressed being obviously quantita- 

 tively variable (Fig. 56), it is easier by selection to modify 

 the modal state of a white-spotted race than of races of most 

 other color varieties. 



That this factor is genetically entirely distinct from albi- 

 nism is shown by the fact that white-spotting is transmitted 

 quite as readily through albinos as through colored indi- 

 viduals. 



In some rodents not only the color factor, but also the 

 extension factor is subject to locally inhibited action. Local 

 inhibition of the extension factor produces yellow spots in an 

 otherwise black, brown, or agouti coat. This color variation, 

 which follows Mendel's law in crosses, may be called yellow 

 spotting. It behaves as a third allelomorph (e') alternative 

 both to full extension (E) and to full restriction (e). When 

 yellow spotting coexists with white spotting, a tri-color con- 

 dition of the coat results, spots of yellow, white, and black 

 (or brown) being found on the same individual. Familiar 

 examples are found among guinea-pigs, cats and dogs. 



Another unit-character variation of certain rodents greatly 

 reduces the production of black and brown pigments without 

 affecting at all the production of yellow pigment. As the 

 pigmentation of the eye consists almost entirely of black or 

 brown, it follows that in this variation the eyes become pink, 

 while the coat pigments other than yellow are greatly reduced 

 in amount. Pink-eyed blacks or browns are very pale coated, 

 but pink-eyed yellows are indistinguishable from other yel- 

 lows except by the eye-color. The changed eye-color is ac- 



