Tyrosinase Mutations Associated with Siamese and Burmese Patterns in the Domestic Cat (Felis Catus)

Home , Birman, Korat, Oriental Shorthair, Ragdoll, Siamese cat, Siberian cat

doi:10.1111/j.1365-2052.2005.01253.x Tyrosinase mutations associated with Siamese and Burmese patterns in the domestic cat (Felis catus)

L. A. Lyons, D. L. Imes, H. C. Rah and R. A. Grahn Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, Davis, CA, USA

Summary The Siamese cat has a highly recognized coat colour phenotype that expresses pigment at the extremities of the body, such as the ears, tail and paws. This temperature-sensitive colouration causes a ÔmaskÕ on the face and the phenotype is commonly referred to as ÔpointedÕ. Burmese is an allelic variant that is less temperature-sensitive, producing more pigment throughout the torso than Siamese. Tyrosinase (TYR) mutations have been sus- pected to cause these phenotypes because mutations in TYR are associated with similar phenotypes in other species. Linkage and synteny mapping in the cat has indirectly sup- ported TYR as the causative gene for these feline phenotypes. TYR mutations associated with Siamese and Burmese phenotypes are described herein. Over 200 cats were analysed, representing 12 breeds as well as randomly bred cats. The SNP associated with the Siamese phenotype is an exon 2 G > A transition changing glycine to arginine (G302R). The SNP associated with the Burmese phenotype is an exon 1 G > T transversion changing glycine to tryptophan (G227W). The G302R mutation segregated concordantly within a pedigree of Himalayan (pointed) Persians. All cats that had ÔpointedÕ or the Burmese coat colour phenotype were homozygous for the corresponding mutations, respectively, suggesting that these phenotypes are a result of the identified mutations or unidentified mutations that are in linkage disequilibrium. Because the same mutations were identified in different breeds with similar phenotypes, the mutations are likely to be identical by descent rather than multiple mutation events occurring at the same site.

Keywords albinism, albino, burmese, domestic cat, Felis catus, siamese, temperature- sensitive, tonkinese, tyrosinase.

Guillery et al. 1974; Halaban et al. 1988; Weber et al. 1978). Introduction Hence, the genes controlling pigmentation play other Several forms of albinism have been recognized in many important physiological roles in mammalian biology besides mammalian species including humans (reviewed in Jackson colouration and potential UV protection. 1997). In man, at least 72 entries are catalogued in Mendelian Albinism variations have been recognized in the domestic Inheritance in Man (http://www.ncbi.nlm.nih.gov/query. cat for several hundred years and documented within the fcgi?db=omim) that have been shown to cause various forms past 100 years (Iljin & Iljin 1930; Tjebbes 1924). The of albinism. Albinism is sometimes associated with other Siamese cat, one of the originally developed cat breeds (Cat medical conditions, such as deafness and immunodeﬁcien- FanciersÕ Association 1993a), has a distinguishing pheno- cies. Thus, albinism mutations, which alter melanocyte pro- type that is a form of albinism. This temperature-sensitive liferation and migration, also have pleiotrophic effects that mutation produces pigment only at the cooler extremities of present as vision, auditory and other abnormalities (Bergsma the body, causing a ÔmaskÕ on the face and darkened paws & Brown 1976; Brown et al. 1971; Elekessy et al. 1973; and tail. This type of albinism is commonly referred to as ÔpointedÕ or ÔHimalayanÕ in non-human species and has been Address for correspondence recognized in rabbits (Aigner et al. 2000), gerbils (Petrij et al.

Leslie A. Lyons PhD, 1114 Tupper Hall, Department of Population 2001) and mice (Kwon et al. 1989). Because the causative Health & Reproduction, School of Veterinary Medicine, University of mutations in these other species have been determined to be California, Davis, Davis, CA 95616, USA. in or are linked to the tyrosinase gene (TYR), it has been E-mail: [email protected] suggested that this temperature-sensitive phenotype in cats Accepted for publication 20 January 2005 is also the result of mutations in TYR (Robinson 1991).

2005 International Society for Animal Genetics, Animal Genetics, 36, 119–126 119 120 Lyons et al.

Tyrosinase is an enzyme required for melanin production suggested as the gene causing the Siamese phenotype. in mammals (Barsh 1996). The locus was originally desig- However, the mutations responsible for the Siamese and nated the color locus (C). Breeding data from cats suggested Burmese phenotypes have not been previously determined. an allelic series with at least three alleles, C > cb > cs Herein presented are two mutations in TYR that are asso- (Robinson 1991). Figure 1 presents the feline coat colour ciated with the Siamese and Burmese phenotypes in the phenotypes for the albinism series. The C allele is completely domestic cat. dominant with normal colour presentation. The Burmese phenotypic variant, cb cb, results in a temperature-sensitive Materials and methods gradient of greatest pigmentation at the points and less on the torso. The well-known Siamese ÔpointedÕ phenotype is cs Sample collection and DNA preparation cs; the fur is pigmented only at the extremities, the torso colouration is very light to white, and the lack of pigmen- Samples from domestic cats were collected by various tation produces blue eye colour. One cat breed, the Tonki- methods including buccal swabs, EDTA anti-coagulated nese, is heterozygous (cb cs) and has an intermediate colour whole blood via venipuncture, or tissues collected post- gradient phenotype to Burmese and Siamese. Several cat mortem. Buccal swab samples were collected at several cat breeds are ﬁxed for the albinism alleles. These include breed shows within the United States and Europe or were Burmese and Singapura for the cb allele, and Siamese, requested from speciﬁc cats and submitted by their owners. Birman, and Himalayan (pointed Persians) for the cs allele. DNA was isolated from buccal swabs following published The Siamese ÔpointedÕ phenotype has been linked to procedures (Young et al. 2005). DNA was extracted from haemoglobin (HBB) protein variants in the cat (O’Brien white cell preparations from whole blood and/or tissues et al. 1986). TYR is on the same chromosome in cats based by standard phenol/chloroform extractions (Sambrook & on synteny to HBB (O’Brien et al. 1986); thus, TYR was Russell 2001).

(a)

(b)

(c) Figure 1 Albinism phenotypes of the domestic cat. a. A seal point Siamese and a seal point Birman with the ÔpointedÕ (cs cs) phenotype; b. A sepai Singapura and a sable Burmese with the burmese (cb cb) phenotype; and c. Tonki- nese with the three different genotypes that segregate within the breed: left to right are a chocolate pointed (cs cs), a chocolate mink (cs cb), and chocolate solid (cb cb) Tonkinese. (Picture courtesy of Karen Plummer, Tintoretto Tonkinese).

2005 International Society for Animal Genetics, Animal Genetics, 36, 119–126 Tyrosinase mutations in the domestic cat 121

FCU40716). Primers were designed from conserved regions Pedigree analysis in each TYR exon using Primer3 (http://frodo.wi.mit.edu/ DNA samples were collected from a UC Davis feline research cgi-bin/primer3/primer3_www.cgi); (Rozen & Skaletsky colony of Persian cats that formed a 60-member multi- 2000) (Table 1) and tested for efficacy in the cat using PCR generational pedigree (Fig. 2) segregating for the ÔpointedÕ conditions as previously described (Lyons et al. 1997) on a phenotype. Phenotypes were determined by visual inspec- Stratagene 96-well temperature Gradient Robocycler tion. Relationships of the cats were verified by parentage (Stratagene, La Jolla, CA, USA). Primers designed for exon 5 testing using 19 microsatellites markers (data not shown). failed to generate product in the domestic cat; therefore, no Three microsatellites markers that flank TYR, FCA076, further analysis of this exon was attempted. The amplified FCA341 and FCA931, were genotyped as previously des- products for exons 1–4 were separated on 1.8% agarose gels cribed (Grahn et al. 2004) and tested for linkage to the at 100 Vh. Gels were visualized by UV exposure after ÔpointedÕ phenotype, which was assumed to be autosomal ethidium bromide staining and photo-documented using a recessive with complete penetrance, using the software Alpha Imaging System (Alpha Innotech Corp., San Leandro, package LINKAGE (Lathrop et al. 1984). Allele frequencies CA, USA). Amplicons were excised from the gel and purified for the analyses were determined from the unrelated cats of using the Qiagen Gel Extraction Kit (Qiagen Inc., Valencia, the pedigree. CA, USA) or PCR products were directly purified using the Qiagen PCR clean up kit (Qiagen Inc.). Purified products were sequenced in both directions using the ABI BigDye Primer design, PCR and sequencing Terminator Sequencing Kit v3.1 (Applied Biosystems, Foster Publicly available sequences from various species were City, CA, USA). Sequencing reactions were separated on an aligned for the gene TYR, including Homo sapien (GenBank ABI 377 DNA Analyzer and the DNA contig sequence was accession no. NM_000372.3), Oryctolagus cuniculus assembled using the Sequencer Software package (Gene (AF210660.1), Canis familiaris (AY336053), Mus domesti- Codes Corp, Ann Arbor, MI, USA). Integrity of the sequence cus (NM_011661), Bos taurus (AY046527) and partial contig was confirmed by visual inspection and verified to be sequences for the domestic cat, Felis catus (AY012029, the correct gene by comparison to sequences in GenBank

592 591 - - - - 3 4 2 4

3217 1250 3218 3221 4480 ------+ + - + 2 4 1 2 2 4 6 7 3 7

3238 5586 4446 44414439 4443 4694 4447 4448 4445 - - 0 0 - + - + - + + - - + - + 4692 - + - + 2 2 3 5 4 6 3 6 3 7 0 0 4 7 3 6 4442 - + 4 6 4 7 - + 3 6 4 7

4305 4631 4633 4904 4906 4699 4912 4911 4444 5072 4908 5337 5339 5160 5162 5164 4698 4702 4907 4909 5340 - + - + - + - + - + - - - + - - - - - + - + 0 0 0 0 + + - + - - - + - - - + - - 0 0 2 7 2 6 2 6 2 74905 2 7 2 4 2 6 2 4 2 3 3 6 4 6 7 7 3 7 7 7 3 7 0 0 2 6 0 0 4 6 3 4 5338 4 7 - + 5161 0 0 5163 4632 4648 2 6 3 4 - + - + - + 3 7 - - 2 7 2 6 5341 5342 3 4 5587 5588 5589 5276 5277 5278 5279 52805281 5529 5530 5531 0 0 0 0 ------0 0 0 0 0 0 3 7 3 4 3 4 2 4 3 4 0 0 3 4 2 2 3 3 2 3 2 3 3 3 2 6 3 6

Figure 2 Pedigree segregating for the ÔpointedÕ phenotype in Persians. Circles represent females, squares represent males, solid symbols indicate phenotypically normal animals and open symbols indicate ÔpointedÕ cats. Diamonds with a slash are stillborn kittens that were not phenotyped. A small ﬁlled circle represents a Ôbreeding nodeÕ for parental cats. Numbers under the symbols represent the laboratory sample number. Ô+Õ indicates a cat that has the normal HpaII site with wild-type sequence and Ô)Õ indicates the lack of the HpaII restriction site for cats that have the ÔpointedÕ mutation. No data is represented by a zero, Ô0Õ. Genotypes for the linked marker FCA931 are represented below the HpaII genotypes. Cat 5586 is an Oriental Shorthair.

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Table 1 PCR analysis of TYR in the domestic Exon Product cat. size size Forward primer (5¢ﬁ3¢) Portion of exon GenBank Exon (bp) (bp)1 Reverse primer (5¢ﬁ3¢) sequenced accession no.

1 1321 785 ctgcctgctgtggagtttc 746/1321 (56%) AY743343 – wildtype agaatgatgctgggctgagt AY743344 – Burmese AY743345 – Persian 2 217 179 tagccgattggaggatacaa 139/217 (64%) AY743346 – wildtype gcagctttatccatggaacc AY743348 – Siamese 3 148 127 cttactgggatagcggatgc 87/148 (59%) AY743349 – wildtype caaatgcatggtgaagaagg 4 182 175 tatttttgagcagtggctcc 128/182 (70%) AY743350 – wildtype ttgtagatagctatagtcatagcccag 12 1321 198 actgcttggagggtctgaaa See above for See above for exon 1 cccatgtactcatctgtgcaa exon 1

1Product lengths exclude primer sequences. 2Primers for exon 1 used for RFLP HpaII typing of the mutation associated with the Burmese phenotype.

using BLAST (Altschul et al. 1990). The human TYR ref- by breeders to screen for ÔpointedÕ; hence, not all indi- erence sequence (NM_000372.3) was used to position the viduals were unrelated. Ten Persian cats are unrelated, cat codons. including five cats that are the unrelated spouses in the TYR exons were then amplified by PCR from genomic pedigree (Fig. 1). DNA of seven cats, including one random bred, three The amplification product is 785 bp for exon 1 and Himalayans (pointed Persians) and three Burmese, using 179 bp for exon 2. The identified SNPs alter normally pre- standard PCR conditions as previously described (Lyons sent HpaII restriction enzyme recognition sites. The exon 2 et al. 1997). Approximately 10 ng of genomic cat DNA G302R mutation disrupts a site that usually generates 62 (2 ll from buccal swab DNA) was used per PCR reaction. and 117 bp products from the 179-bp amplicon. Several PCR parameters included an initial 3 min denaturation at HpaII sites are present in the exon 1 product; thus new 94 C followed by 35 cycles of 1 min denaturation at 94 C, primers (Table 1) were designed that flanked only the HpaII annealing for 1 min at 58 C and a 72 C extension for site that is disrupted by the G227W mutation. These 1 min, followed by a final extension at 72 C for 10 min. primers generate a 198-bp product that produced 80- and Products were isolated and sequenced as described above. 118-bp restriction fragment products using HpaII when the The TYR amplicons were analysed for mutations associ- G227W SNP is present. Approximately 5 ll of amplification ated with the specific phenotypes by sequence analysis. product was digested with 10 U of HpaII (New England Sequences generated from each exon were aligned (DNA- Biolabs, Inc. Beverly, MA, USA) in a 10-ll reaction con- Star, Madison, WI, USA) with wild-type sequence from both taining 1X NEBuffer 4 at 37 C for 3 h followed by inacti- cat and dog to identify possible causative mutations for the vation of the enzyme at 65 C for 10 min. The complete observed phenotypes. When polymorphisms were detected, digestion reaction was analysed on 4% agarose gels as sequence data were translated to determine if the mutation described above. resulted in an amino acid change. GenBank accession numbers for all cat sequences are presented in Table 1. Results A multi-generational pedigree, consisting of 60 cats in PCR-RFLP genotyping which the ÔpointedÕ phenotype segregated (Fig. 2), was Once the mutations were identified, 213 cats, including genotyped for three microsatellites that flank TYR on the five unrelated random bred cats, 158 cats representing genetic map of the cat (Menotti-Raymond et al. 1999, 11 breeds and 50 cats of the UC Davis pedigree, were 2003). The cat phenotypes and the genotypes for marker screened for the ÔpointedÕ and ÔBurmeseÕ mutations using FCA931 are presented in Fig. 2. Significant linkage was RFLP typing on agarose gels. The seven cats used for the detected between the ÔpointedÕ phenotype and microsatellite initial sequencing were included in the 213 cats. The marker FCA931 (Z^ ¼ 5.57, h^ ¼ 0.00). Linkage was not samples represented several ÔfoundationÕ cat breeds and significant between microsatellite markers FCA341 or breeds that are known to be fixed or segregate for the FCA076 and the colour phenotype. albinism phenotypes (Table 2). The Korat, Russian blue, A total of 1100 bp of TYR (46%) was analysed in seven Siamese and Siberian samples represented cats provided cats, including one random bred, three Himalayans (pointed

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Table 2 Tyrosinase (TYR) mutations within 1 different cat breeds. Genotype at residue Breed Number Pattern 227 302

Birman 2 Pointed Not typed R/R Bombay 3 Full colour G/G (2); G/W (1) G/G Burmese 4 Dark gradient shading W/W G/G Korats 75 Full colour Not typed G/G (57); G/R (18) Korats 2 Pointed Not typed R/R Persian 31 Pointed G/G (5) R/R (31); Persian 24 Full colour Not typed G/G (2); G/R (22) Ragdoll 2 Pointed Not typed R/R Random bred 5 Full colour or ÔpointedÕ G/G R/R (2); G/R (1) Russian blue 13 Full colour Not typed G/G (11); G/R (2) Siamese 9 Pointed Not typed R/R (9) Siberians 31 Full colour Not typed R/R (12); G/R (19) Siberians 7 Pointed Not typed R/R Singapura 2 Dark gradient shading W/W G/G Tonkinese 1 Pointed G/G R/R Tonkinese 1 Medium gradient shading W/G G/R Tonkinese 1 Dark gradient shading W/W G/G

1Numbers in parentheses represent the number of cats for each genotype if not all cats had the same genotype. Five Ôpointed PersiansÕ were unrelated and were not part of the Persian pedigree represented in Fig. 2. Five Persians (three ÔpointedÕ and two full colour) were the unrelated spouses in the pedigree.

Persians) and three Burmese (Table 1). The overall homol- recombinants with the ÔpointedÕ phenotype (Z^ ¼ 4.59, h^ ¼ ogy of the feline TYR sequence to human, dog, mouse and 0.0). Fifty-six cats in the pedigree were genotyped for the cow ranged between 83.7 and 93.8%, with dog having the microsatellite markers. The mutation was also completely highest similarity and mouse having the lowest (data not concordant with FCA931 (Z^ ¼ 4.52, h^ ¼ 0.0), but linkage shown). The protein identity ranged from 88.5 to 94.7% to the other two microsatellite markers was not significant. with greatest overall similarity to dog. A comparison of the sequence from the seven cats Discussion revealed three polymorphisms. An exon 1 G > T transversion was identified at position 715 that results in a glycine The Siamese ÔpointedÕ phenotype has been shown to be to tryptophan amino acid change (G227W). An exon 2 linked to haemoglobin (HBB) protein variants in the cat G > A transition was identified at position 940 that causes (O’Brien et al. 1986). The feline microsatellites, FCA076, a glycine to arginine amino acid change (G302R). One FCA341 and FCA931 are predicted to be approximately 17, other SNP was identified in TYR, which was a silent 7 and 1.7 cM, respectively, from TYR in the cat (Menotti- mutation (C > T at nucleotide position 387) in exon 1 that Raymond et al. 2003). Significant linkage was detected was limited to cats in the Persian pedigree (Fig. 2). The between the ÔpointedÕ phenotype and marker FCA931, sequence alignments showing these mutation sites are which is approximately 1.7 cM from TYR on the cat RH presented in Fig. 3. The missense mutations occur in amino map, supporting TYR as the causative gene for the ÔpointedÕ acids that are conserved across several mammals, including phenotype. The G302R mutation was also concordant with humans, mice, dogs and cattle. the ÔpointedÕ phenotype within the pedigree, further sup- Once these mutations had been identified, 208 cats from porting that TYR and the G302R mutation is associated various breeds and five random bred cats with similar with the ÔpointedÕ phenotype. phenotypes were genotyped using RFLP analysis of exon 1 All cats had the anticipated genotypes that corresponded and exon 2 (Table 2). All seven cats from three breeds with to their phenotypes. The 54 cats of seven different breeds the Burmese pattern were homozygous for the G227W SNP with the ÔpointedÕ phenotype were homozygous for the and all 56 ÔpointedÕ cats were homozygous for the G302R G302R mutation. Two ÔpointedÕ random bred cats were also SNP, which represented seven breeds and random breds. homozygous. All cats (n ¼ 7) with the Burmese phenotype Fifty of the cats in the UC Davis pedigree were genotyped were homozygous for the G227W mutation. Cats of differ- by RFLP analyses for the TYR exon 2 G302R mutation. ent breeds and random bred cats had the same mutations Linkage was then tested between the ÔpointedÕ phenotype for similar phenotypes, which lends support to these and the RFLP genotypes. The G302R mutation had no mutations causing the same phenotypes across breeds and

2005 International Society for Animal Genetics, Animal Genetics, 36, 119–126 124 Lyons et al.

190 200 210 220 230 240 YYVSRDTLLGGSEIWRDIDFAHEAPGFLPWHRLFLLLWEQEIQKLTGDENFTIPYWDWRD ....M.A...... A...... R...... Hsap ...... K...... W...... Fcat ...... K...... Cfam ...... RE...... V...... Mmus ...... V...... Ocun ...... D..V...... Btau 2 Figure 3 Protein alignment of feline Tyrosin- 250 260 270 280 290 300 AESCDICTDEYMGGRHPANPNLLSPASFFSSWQIVCSRLEEYNSRQALCDGTPEGPLLRN ase and other species. TYR protein sequences ..K...... Q..T...... H.S..N...... R.. Hsap are aligned from human (Hsap: Genbank .K...... I***********************N...... Fcat Accession no. NM_000372), cat (Fcat), dog .K...... N...... T...... Cfam ..N...... L.....E...... I...S.....H.V...... Mmus (Cfam: AY336053), mouse (Mmus; .....V...... E...... I...... S..NA.SG...... Ocun NM_011661), rabbit (Ocun; AF210660) and ..N..V...... N...... N..S...... Btau cow (Btau; AY046527). The consensus 3 310 320 330 340 350 360 sequence is presented as the ﬁrst line and PGNHDKARTPRLPSSADVEFCLSLTQYESGSMDKAANFSFRNTLEGFASPLTGIADASQS amino acids represented by the standard one ...... S...... Hsap letter code for amino acids. The 5¢ portion of .R...... *************N...... Fcat the protein sequence from exon 1 and the ...... D...... Cfam ...... K...... RT...... P... Mmus 3¢ portion of the protein sequence from exon 5 ...... S...... N...... I.. Ocun are not shown. Numbers above the consensus ...... D.V...... Btau indicate amino acid residue position from the 4 370 380 390 410 420 start of translation. Asterisks (*) indicate miss- SMHNALHIYMNGTMSQVQGSANDPIFLLHHAFVDSIFEQWLRRHHPLQEVYPEANAPIGH ing data and ﬁlled arrows (.) indicate exon ...... Q..R...... Hsap boundaries with the number of the exon listed ...... *******...... Fcat above the arrow. Temperature sensitive TYR ...... P...... R...... Cfam ...... F...... R..L...... R Mmus mutations for each species are indicated in bold ...... M...... R...... A...... Ocun underline within the alignment. The wild-type ...... P...... KY....D...... Btau sequence for each species is presented in the 5 430 440 450 460 470 480 consensus sequence in all instances except NRESYMVPFIPLYRNGDFFISSKDLGYDYSYLQDSDPDIFQDYIKPYLEQASRIWPWLLG Ocun D358 where the wild-type amino acid is ...... S...... S...... S.... Hsap threonine (T). The cat mutation consistent with ...... R...... *************************** Fcat the ÔpointedÕ phenotype is the G302R in exon 2 ...... L....R...... N..E.ER...... I. Cfam ..D...... T...... E...GFYRN..E...... Mmus and the mutation consistent with the Burmese ...... R...... F..G....L...... V. Ocun pattern of gradient shading is the exon 1 ...... I...... E...... Q...... I. Btau G227W mutation.

that the breeds are likely identical by descent for the same with this phenotype (Petrij et al. 2001). These variants mutation. Otherwise, the same mutation has occurred cause amino acid changes from glutamic acid to glycine repeatedly in the cat population. Each of the two mutations and threonine to isoleucine, and are found in exons 2 occurs on the wild-type allele, and G302R/G227W com- and 3, respectively. The cat mutation is found at nuc- pound heterozygotes produce cats with intermediate colo- leotide 715 and the rabbit mutations are slightly more uration, as seen in the Tonkinese breed. downstream at nucleotides 881 and 1073 (Aigner et al. Both of the SNPs that are associated with the coat colours 2000). are conserved amongst dogs, human, mice, cattle and rab- Complete albino cats have been sporadically reported in bits, further supporting that these are significant amino acid the literature but have not been well documented (Turner alterations for the protein. The mutations identified for the et al. 1981). Also, blue-eyed vs. pinked-eyed albino cats two SNPs in the cat result in significant amino acid chan- have not been clearly distinguished in published reports ges. The SNP associated with the ÔpointedÕ phenotype is a (Bamber & Herdman 1931; Leventhal 1982; Leventhal transition in exon 2 at nucleotide 940 that causes an amino et al. 1985; Todd 1951). Thus, it is unclear as to whether acid change from glycine to arginine. Similar temperature- there are more than one albinism allele in the cat, as has sensitive phenotypes in rabbits (Aigner et al. 2000), gerbils been reported for the mouse (reviewed in Beermann et al. (Petrij et al. 2001) and mice (Kwon et al. 1989) result from 2004), humans (summarized at http://albinismdb.med. mutations in various different sites within TYR. Humans umn.edu/) and in cattle (Schmutz et al. 2004). Hence, also have a temperature-sensitive TYR mutation, although additional alleles at TYR may exist for blue-eyed and the phenotype is not as seen in other mammals (Tripathi pink-eyed albino cats. et al. 1991). In the United States, there are approximately 50 cat The SNP associated with the Burmese phenotype is breeds, some of which are hybrids with wildcat species and found in the coding sequence of exon 1, resulting in a long-haired and short-haired varieties of the same breed. glycine-to-tryptophan amino acid change. In rabbits, the Not all breeds or colours are accepted by different cat fancy Burmese colouration is termed ÔchinchillaÕ and two nuc- organizations, but basically there are four breeds (Siamese, leotide variants have been identified that are concordant Birman, Balinese and Javanese) that are fixed for ÔSiameseÕ

2005 International Society for Animal Genetics, Animal Genetics, 36, 119–126 Tyrosinase mutations in the domestic cat 125 points, and three breeds (Burmese, European Burmese and References Singapura) that are fixed for the ÔBurmeseÕ allele. Tonkinese Aigner B., Besenfelder U., Muller M. & Brem G. (2000) Tyrosinase cats are heterozygotes for these two alleles, hence matings b b s s gene variants in different rabbit strains. Mammalian Genome 11, produce c c Tonkinese, known as solids, and c c Tonki- 700–2. nese that are known as colour points. Variations of pigment Altschul S.F., Gish W., Miller W., Myers E.W. & Lipman D.J. (1990) intensity can be due to environmental factors and interac- Basic local alignment search tool. Journal of Molecular Biology tions with other pigment genes causing dilution. Thus, the 215, 403–10. shade of Tonkinese cats does not always clearly indicate the Bamber R.C. & Herdman E.C. (1931) Two new colour types in cats. underlying TYR genotype, but the genetic tests for the cs Nature 127, 558. and cb alleles could be used to assist breeders in selected Barsh G.S. (1996) The genetics of pigmentation: from fancy genes matings and proper colour registration. to complex traits. Trends in Genetics 12, 299–305. Approximately 13 breeds have desired segregation for Beermann F., Orlow S.J. & Lamoreux M.L. (2004) The Tyr (albino) locus of the laboratory mouse. Mammalian Genome 15, 749–58. the cs and/or cb alleles (Cat FanciersÕ Association 1993b). A Bergsma D.R. & Brown K.S. (1976) Animal models of albinism. few other breeds have the cs and/or cb alleles in their gene Birth Defects Original Articles Series 12, 409–13. pool but the resulting colour variants of the homozygous Brown K.S., Bergsma D.R. & Barrow M.V. (1971) Animal models of genotypes are not recognized in the breed and hence, the pigment and hearing abnormalities in man. Birth Defects Original alleles are undesired. Korats are recognized in only one col- Article Series 7, 102–9. s our (blue) but c segregates in this breed, producing unde- Cat FanciersÕ Association (1993a) Siamese. In: The Cat FanciersÕ sired ÔpointedÕ cats. Approximately 30% of the Korats tested Association Cat Encyclopedia (Ed. by Cat FanciersÕ Association), were either pointed or carriers. An accurate allele frequency pp. 128–36. Simon & Schuster, New York. could not be determined from this study population as many Cat FanciersÕ Association (1993b) Show standards. In: The Cat of the cats were related and information on all the relation- FanciersÕ Association Cat Encyclopedia (Ed. by Cat FanciersÕ ships was not available. This breed has a very limited Association), pp. 155–94. Simon & Schuster, New York. Elekessy E.I., Campion J.E. & Henry G.H. (1973) Differences between population size; thus, the eradication of cats that have only a the visual fields of Siamese and common cats. Vision Research 13, single undesirable allele, such as point restriction, could be 2533–43. detrimental to the genetic diversity of the population. Grahn R.A., Biller D.S., Young A.E., Roe B.A., Qin B. & Lyons L.A. The Siberian cat breed is not a well established breed; (2004) Genetic testing for feline polycystic kidney disease. Animal hence, the ÔpointedÕ mutation is of less concern but breeders Genetics 35, 503–4. would like to identify the carriers. Nearly 68% of the Sibe- Guillery R.W., Casagrande V.A. & Oberdorfer M.D. (1974) rians tested were either pointed or carriers, hence this allele Congenitally abnormal vision in Siamese cats. Nature 252, is prevalent within the breed and eradication would sub- 195–9. stantially limit the current gene pool. Only 15% of Russian Halaban R., Moellmann G., Tamura A., Kwon B.S., Kuklinska E., blues tested were carriers for ÔpointedÕ, thus, the mutation Pomerantz S.H. & Lerner A.B. 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