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Coat Color Genetics ofPeromyscus: II. Tan Streak—A New Recessive Mutation inthe Deer Mouse, P.maniculatis

L. R. K. Wang, J. P. Crossland, andW. D. Dawson

The first mutant tan streak deer mice ap-peared in the initial laboratory-bred genera-tion of a stock of Peromyscus maniculatusnubiterrae collected in Macon County, NorthCarolina. Laboratory progeny from the origi-nal animals were bred and mated among

themselves and to wild-type individuals. Thetan streak phenotype is characterized bynearly complete absence of coat pigmenta-tion, except for a pale tan patch or narrowstripe extending mid-dorsally posteriorly fromthe head. The band is frequently somewhatbroader in the shoulder region, occasionallyforming a cross-shaped pattern. There is noevidence of black eumelanin in any part ofthe coat. The eyes are fully pigmented, ap-pearing black, and pigment is present in theskin of the ears and elsewhere. The trait isinherited as an autosomal recessive. The ge-netic locus is provisionally designated tns.Crosses between homozygous tan streak (tns/tns) animals and albino (c/c), ivory (Hi), non-

Figure 1. (A) Tan streak deer mouse compared with (B) wild type.

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Table 1. Inheritance of the tan streak (tns) color trait in Peromyscus maniculatus

Phenotype AnalysisMating class

Female

+ /+ X

tns/tns x

+/tns x

+/tns x

tns/tns x

tns/tns x

Male

tns/tns

+/+

+/tns

tns/tns

+/tns

tns/tns

No. ofmatings

3

2

4

4

5

5

Obs.

Exp.

Obs.

Exp.

Obs.

Exp.

Obs.

Exp.

Obs.

Exp.

Obs.

Exp.

Wild type

Female

22

28.5

4

2.5

27

29.25

16

16.5

7

8

0

0

Male

35

28.5

1

2.5

30

29.25

23

16.5

8

8

0

0

Tan streak

Female

0

0

0

0

13

9.75

16

16.5

10

8

17

21

Male

0

0

0

0

8

9.75

11

16.5

7

8

25

21

RatioX2

dfP

RatioX2

dfP

RatioX2

dfP

RatioX2

dfP

RatioX2

dfP

RatioX2

dfP

Segre-gation

1:0

1:0

3:10.1541.7-.6

1:12.1821.2-.1

1.10.1251.8-.7

0:1

Sex

1:12.9651.10-.05

1:11.81.2-.1

1:10.0511.9-.8

1:10.0611.9-8

1:10.1251.8-7

1:11.5241.3-.2

Inter-action

1:10.82114-.3

1:12.1821.2-.1

1:10.5001.5-.4

Total

3:3:1:11.5903.7-.6

1:1:1:14.4243.3-2

1:1:1:10.7503.9-.8

agouti (a/a) and brown (bib) deer mice pro-duced only wild-type progeny, indicating thatthe tns mutation is not at any of these loci.

In 1986 a group of Peromyscus maniculatusnubiterrae (Cloudland deer mouse) werecaptured in the southern Blue RidgeMountains of Macon County, North Caro-lina, to establish a small breeding colonyat Clemson University. All of the founderanimals were wild type. The following yearthe first tan streak deer mouse, a male,appeared from a mating between wild-caught animals. The initial male tan streakanimal was mated with eight females toproduce wild-type heterozygotes and,subsequently, with his heterozygous prog-eny to produce other tan streak deer mice.Heterozygous half-sibs were mated to pro-duce additional tan streak animals. Themode of inheritance was determined fromthese and subsequent crosses. Additionaltan streak animals were bred at the Uni-versity of South Carolina Peromyscus Ge-netic Stock Center and were crossed to P.m. bairdii stock to improve fertility. Fur-ther formal genetic analysis was conduct-ed at the Stock Center, where a line ofthese animals continues to be maintained.

DescriptionThe tan streak trait is evident within a fewdays of birth, since the affected deer miceare markedly paler in color than their wild-

type counterparts. The phenotype is fullyexpressed by weaning. Superficially, thecoat is white with a pale tan streak ex-tending along the mid-dorsal line from abroader tan patch in the shoulder region(Figure 1). The patch with the dorsal streakforms a cross pattern in some animals. Thedorsal stripe may be much abbreviated insome specimens and evident only in thecervical area, while in others it may extendto the base of the tail. Typically the streakextends about one-half to two-thirds thelength of the body.

Microscopic examination of hairs fromthe pigmented mid-dorsal stripe shows thatthe stripe contains mostly hairs with sparsetan-yellow pigment granules along thelength, but the pigment is somewhat moreconcentrated in the distal 40%. There isno distinct agouti band. However, con-strictions in the individual hairs are pres-ent. The pigment has more an aspect ofbrown eumelanin than of phaeomelanin.Some hairs have occasionally large pig-ment clumps. A minority of hairs in thestripe are devoid of pigment. A given hairtends to contain color granules along mostof its length, or else not at all. Pigment iscompletely absent in the lateral white por-tion of the coat.

The eyes are fully pigmented. The earsand tail stripe are pigmented but are muchpaler and more tan than in the wild type.The scrotum is also lightly pigmented.

Tan streak deer mice are not deaf. Theyrespond to auditory stimuli, unlike severalother partially white coat color mutants inmammals (Searle 1968; Silvers 1979).

InheritanceTan streak is inherited as a simple auto-somal recessive trait (Table 1). No signif-icant deviations (.05 level) from the ex-pected ratios were observed among the 23matings and 280 progeny classified. Bothwild-type males and mutant females wereproduced from backcrosses between mu-tant females and presumptive heterozy-gous males, thus excluding sex linkage. Nosignificant interaction between sex andphenotype was detected.

Interactions with four other recessivecoat color mutations in Peromyscus weretested (Table 2). Crosses between tanstreak and homozygous albino (c/c), ivory(//()• nonagouti (a/d), and brown (6/6)color mutants produced wild-type proge-ny in each instance, indicating that tns isnonallelic with genes for these pelage col-ors.

Forty-nine F2 progeny from the tan streakx non-agouti cross (F, = +/tns +/d) weretyped for coat color upon speculation thata "black streak" interaction phenotypemight be produced, since such a variantwas recently observed in the white-footedmouse, P. leucopus (see Discussion). Noblack streak animals occurred among the

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Table 2. Tests for allellsm between tan streak and other coat colors in P. maniculatus

Cross N,_ , No. of progeny obtained

Female MaleNo. ofmatings Wild type Mutant

Tan streakIvory (i/i)Tan streakTan streak

albino (c/c)tan streaknonagouti (.a/a)brown (6/6)

3111520

F2's, although three were expected. How-ever, the phenotypic ratio from the crosswas 25 wild type: 6 nonagouti: 11 typicaltan streak: 7 diffuse tan. The latter pheno-type at weaning appeared somewhatgrayish-tan, later molting to a diffuse paleorange tan, over much of the head, back,and shoulders without a distinct mid-dor-sal streak. The observed phenotypes areconsistent with a 9:3:3:1 Mendelian ratio(X2 = 6.76, .2 > P > .1); or a 9:3:4 ratio ifthe tan streak and diffuse tan phenotypesare pooled (x

2 = 4.04, .2 > P> .1). Delim-itation of "tan streak" from "diffuse tan"is not absolute, since classification of someindividuals is arbitrary. Under the as-sumption that no nonagouti tan streak an-imals were represented in the F2, the de-viation from the expected is highlysignificant (x

2 = 12.86, P < .005). Appar-ently, the tan streak phenotype is essen-tially epistatic to the agouti locus, sincenonagouti tan streak animals cannot beidentified with certainty from agouti tanstreak individuals.

Discussion

Tan streak is a newly detected locus in thedeer mouse and differs from any other pre-viously described mutant phenotype in thisspecies. Among known color loci in Pero-myscus, albino (c), ivory (/), and brown(ft) were considered possibly homologouswith the tan streak locus. In the deer mouse,as in other mammals, true albinism is dueto an autosomal recessive gene (c) (Sum-ner 1922), which results in the absence oftyrosinase activity (Foster and Barto 1963).In other species, but not in Peromyscus,additional mutant alleles occur at the clocus, including c" in Himalayan rabbitsand Siamese cats, and c°h in chinchilla rab-bits. These additional alleles produce par-tially pigmented animals, but the colortends to be concentrated on the extremi-ties, unlike the situation in tan streak(Searle 1968).

The ivory mutation (/) in Peromyscus alsoproduces extremely diluted, nearly allwhite animals. Ivory is also inherited asan autosomal recessive trait (Huestis 1938).

Unlike albino, ivory deer mice have an off-white pelage with the base of the fur slight-ly beige-gray. Albino and ivory representdistinct loci with complementarity be-tween the wild-type alleles (Huestis 1938).Thus, the albino (c/c + / + ) x ivory (+ /+i/i) cross produces all wild-type (+/c +/0 Fi progeny, as does the cross of tanstreak animals with either of these vari-ants.

The brown mutation (ft) has been re-covered several times in Peromyscus(Dawson et al. 1969; Homer and Dawson1993) and phenotypically is like brown inMus and Rattus. The brown mutation ap-parently affects the amount of melaninsynthesized from 3,4-dihydroxyphenyla-lanine (DOPA) relative to 5,6-dihydroxy-indole (Murray et al. 1983). Since onlybrown melanin granules occur in tan streakanimals, and tan streak apparently doesnot interact with nonagouti to produceblack melanin, the action of the tan streakmutation resembles brown. However, theextensive white on these animals is nottypical of brown locus variants in otherspecies (Searle 1968; Silvers 1979). Theabsence of allelism between tan streak andbrown, ivory, albino, and agouti suggestsa mode of action different from any of these.

Hooded (/?//?) is a recessive variant inrats (Rattus norvegicus) that shares somephenotypic similarity to tan streak (Searle1968). The extent of the dorsal streak com-mon in hooded rats varies greatly de-pending on background modifiers, and thespecific color of the streak is determinedby the other pigmentation factors present(Weisbroth 1969). Thus in hooded rats withotherwise wild-type coat color factors, thestreak (and hood) would be the undilutednormal agouti pattern. In this respect tanstreak differs from hooded in that thestreak is extremely diluted with no evi-dence of normal agouti hairs.

A white-footed mouse (P. leucopus~) witha dark blackish streak was recently foundin a captive stock by George Smith (per-sonal communication). Except for the col-or of the streak, this mouse had a phe-notype resembling tan streak. The deermouse and white-footed mouse are not in-

terfertile; thus, it is not possible to directlytest these two variants for allelism.

Originally, this mutant was informallydesignated "tan mane," but "tan streak"better describes its typical expression.Therefore, the designation tan streak(symbol tns) is proposed for this locus.From the Department of Zoology, Clemson University,Clemson, South Carolina (Wang), and the Departmentof Biological Sciences, University of South Carolina,Columbia, South Carolina 29208 (Crossland and Daw-son). A portion of this study was conducted at thePeromyscus Genetic Stock Center, which is supported,in part, by NSF grant no. DIR-9000352. We thank J.Barnsdale for his assistance in organizing the data andC. Joyner, J. Ruff, and A. Lawson for providing excel-lent animal care. Photographs by C. Cook. Reprintsshould be requested from Dr. Dawson at the addressabove.

The Journal of Heredity 1993:84(4)

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Coat Color Genetics ofPeromyscus: III. Golden-Nugget—A Recessive Trait inthe White-Footed Mouse,P. leucopus

B. E. Horner and W. D. Dawson

A novel pelage color variant appeared in alaboratory colony of white-footed mice (Pero-myscus leucopus) from Massachusetts. Themature adult coat color of this variant exhibitsa rich golden tan appearance on the dorsumwith white underparts. The trait is inherited as

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