76'4 



PHYSIOLOGIC GENETICS 



tyrosine, under control of the enzyme tyrosinase, firmly linked with protein. 1192 The 

 specificity of the enzyme seems to depend primarily on the c series of alleles which 

 is interpreted as acting pleiotropically on the phaeomelanic and eumelanic processes 

 (13 and 19 respectively in figure 22). The complete or very nearly complete domi- 

 nance of C in all combinations indicates that its product is in excess in both reactions 



Fig. 24. EUMELANIN AND PHAEOMELANIN IN GUINEA PIGS. 



c°c° c r c° cV c d c° cV c d c d c k c° c k c r c k c d c k c k C 



(sisi-n-) 



c a c a c r c a c r c r c d c a c d c r c d c d c k c a c k c r c K c d C K c k C 



Estimates of amounts of eumelanin (above) in guinea pigs of genotype EBP and of 

 phaeomelanin (below) in ones of genotype eeFF, associated in both cases with the various c 

 compounds and with to 4 plus factors at the loci Si, si; Dm, dm. Comparable with 

 figure 23. 



while the intermediacy of heterozygotes among the other alleles indicate that their 

 products are limiting factors in both. The evidence as a whole indicates the order in 

 amount of product to be C > c k > c d > c r > c a but the actual orders of intensity 

 vary from case to case (figure 23). The lower alleles are interpreted as competing 

 (20 in figure 22) for processes 13 and 19 with different degrees of efficiency in order to 



