No. 640] DATA CONCERNING LINKAGE IN MICE 413 



A great amount of data has been obtained by breeding 

 the house mouse. Yet a further intensive study is desir- 

 able of the mutant characters discovered, especially as 

 regards linkage, for from such study alone can be de- 

 duced the probable localization of the genes in the chro- 

 mosomes. According to Harvey (1920), the number of 

 chromosomes in the gametes of the house mouse has been 

 estimated by different observers at from 8 to 30, the 

 more recent observers placing the number at from 20 to 

 24. One of these is probably a sex chromosome which is 

 heterozygous in the male and homozygous in the female. 

 In this sex chromosome is apparently located the lethal 

 gene of the Japanese waltzing mouse reported by Little 

 (1920). In one autosome are located the linked genes 

 for pink-eye and albinism. In another autosome must 

 be located the gene for agouti and its allelomorphs, non- 

 agouti, light-bellied agouti, and yellow; to a third auto- 

 some is referred piebald spotting; to a fourth, black- 

 eyed- white spotting; while dilution and its allelomorph, 

 intensity, will probably have to be referred to a sixth 

 autosomal group. Thus seven of the twenty or more 

 chromosomes are genetically identilied, leaving thirteen 

 or more yet to be identified with visible characters or 

 niiitatioiis yet to be discovered. 



Annum- imxlifying genes in mice, Little (1915) and 

 Dunn ( I'.d'd) liave shown that the ''blaze" or "white- 

 face" variation which modifies the piebald pattern is 

 heritable. Dunn (1920) also reports a "belly-spot" to 

 segregate independently of self and piebald, tliough ap- 

 parent only in animals lieterozygous for self and piebald. 

 Gencrnl modify in, factors, inei-casing or decreasing the 

 mva ..f pi-nirnt in thr 1)lnck-c\ r.l-wliitr ami piebald pat- 

 Xvru>, arc also hrritahlc Vrvy littlr is kno\\Ti at the 

 present time concerning thcso modifying factors, and 

 nothing about their linkage relations. 



