238 BIOLOGY OF THE LABORATORY MOUSE 



r rodless retina.— Chiomosome 4. Probably linked with silver (about 

 12% crossing-over). Keeler, 1930, Bull. Howe Lab. Ophthalmology 3:111. 

 Rods lacking or reduced in number. Blind. Keeler, 1925, Anat. Rec. 31: 341. 



Re rex. — Phenotypically similar to or identical with Ca. Crew and 

 Auerbach, 1939, J. Genet. 38: 341-344. 



5 piebald. — Chromosome 3 (see hr). White spotting. There is always 

 a white area on the belly, usually one on the back, often a white blaze on 

 the head, but the amount and location of the spotting is variable, being 

 affected by both modifying genes and environment. In one ''all-white" 

 strain 99% of the dorsal area, on the average, is white, but this has been 

 shown to be due to a group of "k" genes capable of causing 3 to 35% dorsal 

 white in the absence of s. Ss mice may show some white, particularly on 

 the belly. Dunn and Charles, 1937, Genetics 22: 14-42. 



Sd short-Danforth. — In heterozygotes the tail is shortened, terminating 

 in a contorted filament, or lacking; sacral region frequently shortened due 

 to malformations of the sacral vertebrae; one or both kidneys may be 

 reduced or missing. Viability reduced. In homozygotes tail is lacking 

 and spinal column shortened, usually terminating at the second lumbar 

 vertebra; anus imperforate; kidneys absent; bladder and urethra sometimes 

 absent. Do not survive more than 24 hours after birth. Dunn, Gluecksohn- 

 Schoenheimer and Bryson, 1940, J. Hered. 31: 343-348. 



se short-ear. — Chromosome 2 (see d). The ears do not grow after 14 

 days thus remaining quite short. Prior to 14 days cannot be distinguished 

 from normal sibs. The gene produces several other minor effects, in particu- 

 lar a muscular waviness of the tail that disappears in etherized animals. 

 Lynch, 1921, Am. Nat. 55: 421-426. Snell, 1935, Genetics 20: 545-567. 



sh-i shaker-i. — Chromosome i (see C). Nervous, rapid, up and down 

 movements of the head. Internal ear histologically normal up to 12 days, 

 thereafter abnormalities appear which are later accompanied by deafness. 

 Recessive, except that Sh-ish-i Vv mice usually go deaf at from 3 to 6 

 months of age. Lord and Gates, 1929, Am. Nat. 63: 435 442. Griineberg, 

 Hallpike and Ledoux, 1940, Proc. Roy. Soc. B 129: 154-173. 



sh-2 shaker-2. — Chromosome 7. Linked with u'a-2 (25% crossing-over). 

 Snell and Law, 1939, J. Hered. 30: 447. Nervous movements of the head 

 which are indistinguishable from those of sh-ish-i mice. Clark, 1935, 

 Proc. Nat. Acad. Sc. 21: i^'j-i^i. 



si silver. — Chromosome 4 (see r). Some of the hairs in coat partly or 

 wholly unpigmented. Quite variable. The silvering is more pronounced 

 when one h gene or one W^ gene is present. Ordinarily recessive, but partly 



