DATA COXCERXrXG LINKAGE IN MICE 



M . WACHTER 



Ii^ exploiting the genetics of any plant or animal it is 

 of great importance to breed intensively and extensively 

 until the genetic material is exhausted. Even after the 

 dominance or recessiveness of a certain gene has been 

 established, there yet remain to be determined the rela- 

 tionships between this and other genes known to consti- 

 tute the hereditary complex of that particular plant or 

 animal. These possible relationships are allelomorphic, 

 independent, or linked. Mendel was able to formulate 

 certain laws of heredity from the data he obtained in his 

 breeding experiments; but had he continued his work to 

 include other factors he would undoubtedly have been 

 led to predict or formulate a theory of linkage. The 

 chromosome theory of heredity involves independent in- 

 heritance of genes which lie in different chromosomes no 

 less than linked inheritance of those which lie in the 

 same chromosome. It is equally important in relation 

 to this theory to know whether two genes are linked or 

 not linked. 



A very meager amount of linkage has so far been found 

 in mammals. Cases have thus far been observed only in 

 rabbits, rats, and mice. In rabbits Castle (1920) has 

 recently shown that there is a probable linkage between 

 the factors for dilution and the English type of spotting. 

 In rats Castle and Wright (1915), and Castle (1919), 

 had previously shown albinism, red-eye, and pink-eye to 

 be included in the same linkage system. In mice the 

 genes for pink-eye and albinism were first shown to be 

 linked by the work of Darbishire (1904), as was pointed 

 out by Haldano, Sprunt, and Haldane (1915), who con- 

 firmed the idea by observations of their own. 



412 



