Studies on the Tricolor Pattern of the Guinea Pig. Ii. The Distribution of Black and Yellow as Affected by White Spotting and by Imperfect Dominance in the Tortoise Shell Series of Alleles

Abstract

HE tricolor pattern of the guinea pig can be analyzed into two com-T ponents: (I) the pattern of color and white and ( 2 ) the pattern of black and yellow. The former has been considered in the previous paper Pattern of black and yellowThe tortoise shell pattern consists of yellow hairs sprinkled lightly among black hairs in a few irregular, asymmetrical regions over the body. This is the typical pattern of family D, a highly inbred strain which never shows white. Occasionally a foot has a small area of segregated yellow at the tip. Large areas often appear to be solid black.The tricolor pattern of black, yellow, and white, was a feature of the earliest scientific description of the guinea pig. According to CUVIER this variety was described by ALDROVANDUS about 1550 (CASTLE 1912).Compared with the tortoise shell, the tricolor has a tendency to greater segregation of black and yellow hairs (WRIGHT 1917), giving typically i n addition to some brindling clear areas of black, yellow, and white. The individual irregularity of the black-yellow pattern is even greater than for the color-white pattern.In 1916 IBSEN proposed the symbol e p (partial extension of black) for the gene determining the tortoise shell pattern. Later (1919) he reported on the inheritance of the three alleles at this locus, E (self black) dominant over e p and e (self yellow), and e p dominant over e. The question of dominance in multiple allelic series is interesting and a quantititve study has been one of the objects in the present investigation.No statistical analysis of the array of. modifiers of this pattern has been made but the existence of such modifiers will be shown by differences in average number of yellow hairs in certain experiments.1 Submitted in partial fulhlment for the degree of Doctor of Philosophy at the University of Chicago.2 The author is grateful to PROFESSOR SEWALL WRIGHT of the University of Chicago for the suggestion of this problem, the use of pattern records, the facilities for breeding experiments, and the constant stimulating guidance throughout the work. The guinea pig colony has been maintained under a grant to the University of Chicago from the Rockefeller Foundation.