Cnapter 5 



GENE AND CHROMOSOME MUTATIONS 



Bv George D. Snell, Roscoe B. Jackson Memorial Laboratory. 



Gene mutations, 234. Characters inherited in an irregular or undetermined manner, 

 240. Induced chromosome mutations, 242. Rules for assigning symbols to muta- 

 tions, 242. The chromosomes of the mouse, 243. Negative linkage data, 244. 

 Bibliography, 246. 



Gene Mutations 



In the following list of gene mutations are given (j) the symbol for the 

 mutation adopted by the International Committee on Mouse Genetics 

 Nomenclature; (2) the name of the mutation; (j) if a linkage is known, (a) 

 the number of the chromosome to which the linkage group has been assigned, 

 {h) the per cent of crossing-over between the known genes on this chromo- 

 some, (c) a reference to an article giving linkage data; {4) a brief description 

 of the mutation; (5) a statement as to the dominance shown by the mutation 

 (if no statement is made about dominance it may be assumed that any 

 mutation represented by a small letter is completely recessive to its normal 

 or type allele); {6) a reference to one or more important, and if possible 

 recent, articles describing the mutation. 



A agouti. — Chromosome 5. Linked with pa (20% crossing-over). 

 Roberts and Quisenberry, 1935, Am. Nat. 69: 181-183. The normal or 

 type allele of the agouti locus. 



a non-agouti. — aa mice are solid black, lacking the sub-apical yellow 

 band on each hair which gives wild-type mice their characteristic brownish 

 color. In most stocks a is completely recessive to +, but strains have been 

 reported in which +a mice have a dark or black back merging into nearly 

 typical agouti on the sides and belly. In these strains -f-f mice are only 

 slightly darkened. There is some evidence that one principal partly domi- 

 nant modifying gene, umbrous {U), is involved. Mather and North, 1940, 

 J. Genet. 40: 229-241. 



a' black-and-tan. — Allele of a. Mice of the constitution a'a^ and a^a 

 have a light belly (dirty yellow to white) and a black back. The line of 

 demarcation between light and dark regions is quite sharp. Aa*^ mice have 

 a light belly and an agouti back. Dunn, 1916, Am. Nat. 50: 664-675. 



234 



