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THE AMEBIC AX .V.I TV I! A LIST [Vol. LTV 



We may therefore conclude that the known genes in 

 rats arrange themselves into three gronps. Into one may 

 be placed agouti (-4) and its allelomorph, non-agouti (a); 

 into the second, self (S), with its allelomorphs, Irish (Si) 

 and hooded (Si,) ; and into the third the three genes R, P 

 and C with their allelomorphs. 



As before stated, Castle showed that R and P were 

 linked to albinism (CV,), but he did not determine the ex- 

 act degree of their linkage. 5 Evidence on this point 

 concerning the linkage of R and C„ will be presented in 

 the following pages. 



Two of the heterozygous self agoutis (rSA-RSna) used 

 in determining the linkage relations of R, S and A, when 

 mated together produced some albino offspring. The 

 father of the self agoutis, $ 105A.1, a red-eyed self, 

 carrying agouti (rrSSAA), could not have carried al- 

 binism himself since he had 17 non-albino offspring when 

 mated back to one of his daughters, $ 126B.4, known to 

 be carrying the albino gene. The mother of the self 

 agoutis, ? 98A.2, a black-eyed black hooded, must there- 

 fore have been heterozygous for albinism, and accord- 

 ingly would be of the composition RRS„S„aaCCa. Her 

 offspring that gave birth to albinos would of necessity 

 have the zygotic formula RrSStAaCC. These when in- 

 bred should have had albino offspring of various compo- 

 sitions, if there had been no linkage. For every albino 

 that was homozygous for a dominant gene we should have 

 expected two that were heterozygous and one that was 

 homozygous for the recessive. 



Since there were six albinos born from the agouti X 

 agouti mating, it seemed quite probable that one at least 

 would be found that was recessive for all the genes. Ani- 



