356 



Quantitative Characters 



gous. Color genes, however, do not always increase size, for the 

 agouti and albino (c) genes apparently have no effect at all, 

 whereas the genes for pink-eye (p) and leaden (In) retard 



TABLE 20 



Percentage Change in Body Size Effected by Certain Genes and 

 Combinations of Genes in Mice 



(From Castle, 1941.) 



growth. The gene for short ear, se, also retards growth, as does, 

 of course, the gene for dwarf, dw, whose main effect is on size. 



Further studies on these genes in mice show that they do not 

 always act cumulatively as one would expect with polymeric 

 genes. Animals homozygous for both brown and dilution are 

 heavier than those homozygous for either of these genes alone. 

 When brown and nonleaden are homozygous (bb LnLn) body 

 size is greatly increased over homozygous nonbrown nonleaden 

 {BB LnLn) and also over the brown heterozygous nonleaden 

 type [bb Lnln) . Homozygous leaden {BB lnln and Bb lnln) de- 

 creases body size considerably and brown leaden {bb lnln) even 

 more so. 



Some light has been thrown recently on the problem of genes 

 for general body size as contrasted with genes for the size of 



