Exp. Anim. 38(4), 337-341, 1989 Note The Genetics of Coat Colors in the Mongolian Gerbil (Meriones unguiculatus) Tetsuya MATSUZAKI, Yukio YASUDA, and Shuichi NONAKA* Central Institute for Experimental Animals, 1430 Nogawa, Miyamae-ku, Kawasaki-shi 213, Japan and *Koropokkuru Inc., 1741-5 Shinboritsuki Kawarabuki, Ageo-shi, Saitama 362 (Received 18 October 1988/Accepted 26 April 1989) Genetic studies demonstrated three loci cotrolling coat colors in the Mongolian. F1 hybrids of white s with red eyes and agouti s with wild coat color had the agouti coat color. The segregating ratio of agouti and white in the F2 generation was 3 : 1. In the backcross (BC) generation (white ~F1), the ratio of the agouti and white coat colors was 1 : 1. Next, inheritance of the agouti coat color was investigated. Matings between agouti and non-agouti (black) s produced only agouti s. In the F2 generation, the ratio of agouti to non-agouti (black) was 3 : 1. There was no distortion in the sex ratios within each coat color in the F1, F2 and BC generations This indicated that the white coat color of s is governed by an autosomal recessive gene which should be named the c allele of the c (albino) locus controlling pigmentation, and the agouti coat color is controlled by an autosomal dominant gene which might be named the A allele of the A (agouti) locus controlling pigmentation patterns in the hair. The occurrence of the black demonstrated clearly the existence of the b (brown) locus, and it clearly indicated that the coat colors of s can basically be explained by a, b, and c loci as in mice and rats. Mongolian s are found in most of Asia, especially in China, Mongolia and the subcontinent of India, and in Africa. They are also the most common and widely distributed mammal in South Africa. Thirteen subspecies of have been captured and are maintained under laboratory conditions, of these only Meriones unguiculatus is used as an expermental animal [3]. Swanson (1980) has recently described five mutants : nonagouti, acromelanic albino, pink eyed, white spot, and hairless [5]. However, the inheritance of an albino or red eyes and white coat color has not been reported. Recently two pairs of s with red eyes and white coat color were obtained. Also, s with a black coat color were found in our colony. Using three colonies showing different coat colors, agouti, black, and white, we carried out genetic studies on the coat color of the Mongolian. This is the first report on the albino, non-agouti, and black coat colors of s. We propose that the three loci, a, b, and c, used in mice and rats for coat colors should be adopted for the Mongolian. Three colonies with different coat colors maintained in our institute are shown in Fig, l a, b, c, [1, 6]. Mongolian s with the agouti coat color were introduced from the Kitasato Institute (Tokyo, Japan) in 1949 (Fig, 1 a). No coat color variants have been found in 1, 855 s bred in the colony. Two pairs of s with white coat color were introduced from a petshop in Yokohama, Japan in 1985 (Fig, l b). The colony of white coat color s was expanded. So far 313 individuals have been bred, but no variants were found. Gerbils with the black coat color were found in a pair of backcrosses in an
338 investigation of the relation between the agouti and the white coat colors. Gerbils were bred at a temprature of 22 }2 Ž and humidity of 55 }5 %. Air was replaced 10-15 times/hour with fresh air. Animals were accomodated in plastic cages (25w ~35d ~15h cm) with wood shavings for bedding. Sterilized diet (3 M rad irradiated CA-1, CLEA Japan Inc.) and water were provided no itahcs needed. Animals older than three months were used for mating experiments. I. Genetic analysis of the white coat color Mating experiments were carried out to demonstrate inheritance of the white coat color. Table 1 shows the results of mating experiments using white and agouti colonies. The 55 F1 hybrids were obtained by crossing agouti females and white males ; they showed agouti. Matings among F1 hybrids were performed and 94 individuals were obtained. They were separated into two groups by coat color, one agouti and the other white. The ratio of agouti to white coats was 71: 23, and was in good agreement with the 3 : 1 ratio theoretically expected (X2=0.048, 0.8<p< 0.9). Next, backcross matings were performed using the F1 males and white females. Fortytwo of the 81 backcross progenies were agouti and 39 were white. The segregating ratio in the backcross generation was in accordance with the expected ratio, l : 1 (X2=0.111, 0.5<p <0.8). There was no distortion in the sex ratios within each coat color. The mating experiments indicated that the white coat color was controlled by an autosomal recessive gene. Acording not only to the characters but also to the mode of inheritance, the white coat color studied in this paper should be called albino. Therefore the gene controlling non-pigmentation causing albino was named the c allele, and the gene controlling pigmentation the C allele of the c locus. II. Genetic analysis of the non-agouti (black) coat color One backcross pair produced s with three different coat colors. Of 13 s six were agouti, five were albino and two were black. To study the inheritance of the nonagouti (black) coat color, a colony with black coat color has been established. So far 107 progenies have been produced, but no variants have been seen in the colony. Therefore, the colony was considered to be fixed for black coat color. Mating experiments were perfomed to demonstrate inheritance of the agouti coat color. Results are shown in Table 2. First, agouti females were mated with black males, and 28 F1 hybrids were obtained. All of them were agouti. Matings among the F1 hybrids produced 55 individuals of the F2 generation. They were segregated into two kinds of coat colors ; 44 were agout and 11 were black. The segregating ratio in the F2 generation was in good agreement with the expected ratio, 3 : 1 (X2=0.732,0.3<p<0.5). There was no distortion in the sex ratios with in each coat color in the F1 and F2 generations. The data showed that the non-agouti (black) coat color was governed by a single autosomal recessive gene, and the agouti coat colcr was controlled by a single autosomal dominant gene. The gene controlling the agouti coat color was named the A allele of the a locus, and the gene controlling the nonagouti coat color the a allele of the a locus according to the nomenclature of the coat color genes in mice and rats. Robinson (1980) has recently described acromelanic albinism [4]. This is phenotypically similar to albinism without variable amounts of pigment in the extremities (nose, Table 1. Mating experiments for white coat color in the Mongolian
339 ears, feet and tail). Albino s described in this paper show a complete white coat color with red eyes, and there is no pigmentation anywhere on the body. These characters were the same as those in mice and rats. Albino s have been reported [3], but no genetic analyses of the albino coat color were mentioned. This paper appears to be the first one on albinism in the Mongolian. Non-agouti (black) s appeared in our colony. Genetic studies have been carried out, and the modes of inheritance of the agouti and non-agouti (black) coat colors were revealed. So far there have been no reports on black coat color in s so this is the first report on black coat color in the Mongolian. Black s were found in backcross progenies of albino x (agouti X albino) F1. This indicated that the black coat color gene was maintained in the albino colony, but not in the agouti colony. Unfortunately, no brown coat color controlled by an allele of the brown locus has been found. Table 2. Mating experiments in the Mongolian Fig. 1 The appearance of non-agouti (black) s indicated the existence of the a locus controlling pigmentation patterns in the hair, just as in mice and rats. In the agouti hair, there were three regions with different pigmentations (melanin formation). They were black in the extremity, brown in the middle and black in the roots. In black hair, there was a uniform pattern of melanin formation. Our data described in this paper show that the Mongolian has three loci controlling coat colors, the same as in mice and rats [2]. The first locus controlling patterns of melanin formation in hair is called the a locus. This locus was confirmed only after the appearance of s with the black (non-agouti) coat color, although the wild coat color has been considered the same as agouti in mice and rats. The second one is called the b locus, which controls the density of melanin. The third locus is called the c locus, and homozygotes lack the enzyme involved in the for agouti a. Agouti and non-agouti (black) coat colors
340 Fig. Fig. 1 b. 1 c. process of melanin production. The discovery of black s will accelerate the discovery of various coat colors, especially the brown coat color, in the future. So far brown coat color has not been found, but this will not affect our understanding of the coat color genes of Albino Black References [1] [2] [3] s. The authors are grateful to Drs. T. Nomura and Y. Tajima (Central Institute for Experimental Animals) for their valuble suggestions. We also thank Dr. H. Katoh (Central Institute for Experimental Animals) for his valuable discussion and critical reading of this manuscript. [4] [5] [6] Imai, A., Endo, M., Imaizumi, K., and Tajima, Y. (1959). Experimental Animals, 8, 21-29. Kondo, K. (1970). Laboratry Animal Science, pp. 31-65, Y. Tajima. (edit), Asakura, Japan. Norris, M. L. (1987). The UFAW Handbook on the Care and Management of Laboratory Animals, pp. 360-376, Poole, T. B. (edit), Longman Scientific and Technical Publishers, London, UK. Robinson, R. (1973). Genetica, 44, 454-458. Swanson, H. H. (1980). Laboratry Animals, 14, 143147. Tajima, Y.(1963). Experimental Animals, 12, 145179.