GENIC INTERACTION 



161 



to be unsound, 985 the extraordinary number of alleles in some cases (more than 250 

 at the B locus in cattle) and the curious intragenic, interaction effects indicate great 

 complexity of genie pattern and the existence of much primary pleiotropy. 



The association of blood-group genes in man with fetal hemolytic disease and with 

 various diseases of adults demonstrate much secondary pleiotropy. There is no good 

 reason to suppose that multiple allelism and pleiotropy are any less frequent with loci 

 for which such delicate methods of demonstrating differences are unavailable. 



Fig. 22. Diagram of factor interactions in the determination of coat color of the 



GUINEA PIG. 



Predisposition 

 (epidermis) 

 Absence of 

 Melanocyte 

 WHITE 



Differentiation 

 (melanocytes) 



Enzyme system 

 (granules) 



Pigment 

 (from tyrosine) 



Dinginess 



(I) 

 Spotting 



S,s(+) 

 I (Ms) 



d f ,?(+) 

 Dam's age(+) 

 Region 



Chance /\l^ 

 ■ \Spotting 



j Region 



/p» i Chance . 



Silverin g 



Si,si(0 



S(Msi) 



Region 



Chance 



(3) 

 Diminution ^ 



Dm,dm(+) 

 (4) 

 Grizzling 



Eumel. 

 predisp 



Phaeomel. / i 

 predisp. (10) f 



\y f f-(26) 



<( (25) AgeH 2 (Leu) 



b^\ i L- {27) 



- (28)- 



a 



p) 



\Mp,mp(-)| (22)x 

 Spotting ^"-"v 

 AgeH J >f\ 



Gr,gr(+) 

 I (Mgr) 

 Age (+) 

 Region 

 Chance 



Sootine ss 



I (So) 



Region 



Temp.(-) 



Agouti 

 AMXa 

 Z(MA) 

 Region 



\—-^ /_(„)_ -JJc^r^L 



*-SEPIA 



v»-BR0WN 



>YELL0W 



The study of the genetics of metabolic processes in such favorable organisms as 

 Neurospora, Aspergillus, and Escherichia coli has been characterized by the demonstration 

 of long, branching, reaction chains in which each link is controlled by a particular 

 locus. Nonadditive interaction effects are the rule. 1353 Such processes are merely 

 the first steps leading to the variations observed at the morphologic level in higher ani- 

 mals. Figure 21 is intended to represent the hierarchy of levels at which inter- 

 action may occur. 1413, 1424, 1433, 1434, 1441, 1450 The interaction patterns found among 

 the genes concerned with a number of such characters of the guinea pig will be 

 reviewed here. 



