Chapter 5

Grey-Lethal, Grizzled, Mocha, Pallid, Muted, Misty, and Pearl

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VI. Misty (m)

For the m allele:
m Allele (MGI) Gene (MGI) All Alleles (MGI)

A. Origin and Influence on Pigmentation

Misty (m) is a recessive mutation which arose spontaneously at the Jackson Laboratory in the DBA/J strain. It is located on the fourth chromosome, about 7 cM from brown (Woolley, 1941, 1943, 1945). m/m animals are slightly lighter than normal on both nonagouti black and nonagouti brown backgrounds. The mutation was originally described by Woolley ( 1941) who noted that " m/m;b/b;a/a and m/m;B/B;a/a mice are more uniform and more intense in color than ln/ln;b/b;a/a, ln/ln;B/B;a/a or d/d;b/b;a/a and d/d;B/B;a/a mice." The difference between m/m and ln/ln or d/d mice is especially noticeable at the extremities such as the hair tip, ears, and tail where m/m seems to allow more pigment ( Woolley, 1941). Misty mice also display a light underfur which is useful in classification ( Grüneberg, 1952) as well as a very high incidence of white tail tips. A small white belly spot, the incidence of which depends upon the genetic background, may also occur. Woolley ( 1945) reported that whereas none of 64 M/— DBA/J mice displayed a white tail tip or white belly spot, 52 of 53 m/m DBA/J animals had white tail tips and two of these also had a white belly spot. On the other hand, when misty animals were outcrossed he found that all 258 F2 m/m mice had white tail tips (versus 61% in M/— genotypes) and 195/275 (71%) white belly spots (versus 2% in M/— animals). Moreover, in all cases where a white belly spot occurred, whatever the genotype, a white tail tip also was found.

The effect misty has on phaeomelanin synthesis has not been reported.

Microscopic examination of mm hairs reveals much more cortical pigment, and probably slightly more medullary pigment, than in d/d or ln/ln hairs on both a/a;b/b and a/a;B/B backgrounds ( Woolley, 1941).

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