236 BIOLOGY OF THE LABORATORY MOUSE 



d dilution. — Chromosome 2. Linked with sc (.06% crossing-over). 

 Snell, 193 1, Genetics 16: 42-74. The coat is diluted to a blue-gray or leaden 

 color. In aa mice the color is similar to that of a Maltese cat. The pig- 

 mentation of the eyes at birth, as seen through the unopened eyelids, is 

 slightly lighter than in D mice. Little, 1913, Carnegie Instn. Wash. Pub. 

 No. 179: 11-102. 



dw dwarf. — Causes practical cessation of growth at 14 days. Prior to 

 this age there is some retardation of growth, so that by 7 days dwdw mice 

 can usually be recognized by their smaller size. Sterile in both sexes. 

 Due to pituitary deficiency. De Beer and Griineberg, 1940, J. Genet. 39: 

 297-300. 



/ flexed tail. — Tail flexed due to fusion of vertebrae, newborn young 

 anaemic, often accompanied by white spot on belly. The anaemia is due 

 in part to a deficiency in the number of erythrocytes; more important 

 however is a deficiency in the total amount of haemoglobin. It largely 

 disappears at two weeks. The flexed tail condition is recessive with some 

 normal overlaps, perhaps sometimes dominant. Mixter and Hunt, 1933, 

 Genetics 18: 367-387. 



gl grey-lethal. — Homozygous glgl mice, otherwise of wild phenotype, have 

 a pure grey coat without a trace of yellow. In aa or c'^c^ genotypes, the gl 

 gene produces little effect on coat color. There is a major effect on growth. 

 glgl mice are slightly smaller than normals from birth to 14 days, thereafter 

 they loose weight. The teeth do not erupt, their shape is abnormal and the 

 roots uncalcified. The long limb bones are abnormal. Death occurs 

 usually between the 22nd and 30th day. Griineberg, 1938, J. Genet. 36: 



153-170- 



hr hairless. — Chromosome 3. Linked with s (about 9% crossing-over). 

 Snell, 193 1, Genetics 16: 42-74. Homozygous hrhr mice develop normally 

 until about 14 days of age when, at just about the same time that the eyes 

 Open, they can be distinguished from normal sibs by loss of hair on the upper 

 eyelid. At about the same time shedding begins on the under jaw and 

 on all four feet just back of the toes, and slightly later at the base of the tail. 

 During the next week shedding spreads from these centers, especially that 

 around the eye, until the animal is naked except for a few scattered hairs. 

 The vibrissae usually remain. There is sometimes a very slight regeneration 

 of hair at about six weeks. Females are poor breeders or often completely 

 sterile. David, 1932, Z. Zellforsch. u. mikr. Anat. 14: 616-719. 



hr'^'^ rhino. — Allele of hr. At 13 or 14 days hair begins to shed above 

 eyes just as in hrhr mice, but there is less definite anterior-posterior progres- 



