399
Notes In the hybrid N. sylvestris x N. otophora all chromosomes are distinct on the basis of their morphology. To be able to identify each chromosome is particularly valuable, especially as chromosome loss is a property of animal somatic hybrid cells13 and in view of the indications that similar phenomenon is exhibited by plant somatic hybrid cells8 where wide crosses are involved. Even in somatic hybrid plants produced between two sexually compatible species there is evidence of chromosome loss7-11. Consequently the species combination N. sylvestris-N. otophora offers the possibility of determining which particular chromosomes are lost and of answering questions associated with the rate and direction of loss. In addition, exploitation of the heterochromatin spots in the nuclei of N. otophora2 may permit the study of problems concerned with the behavior of nuclei in fusion products. Summary The chromosomes of N. tabacum, N. sylvestris, N. otophora, and the F, hybrids N. tabacum x TV. otophora and N. sylvestris x N. otophora were assessed for their potential as cytological markers in a putative somatic hybrid cell. All acrocentric chromosomes in the cells of N. tabacum x N. otophora are attributable to either parent, but many of the metacentric and submetacentric chromosomes are not unequivocably identifiable. In contrast, in the hybrid A', sylvestris x N. otophora all chromosomes can be attributed to either parent. Literature Cited
2. -. The use of heterochromatin spot counts -andto determine ploidy levels in root tips and callus cultures of Nicotania otophora and its hybrids. Plant Sci. Lett. 7:417— 427. 1976. 3. CARLSON, P.S., H.H. SMITH and R.D. DEARING. Para-
sexual interspecific plant hybridisation. Proc. Nat. Acad. Sci. (U.S.) 69:2292-2294. 1972. 4. GERSTEL, D.U. and J.A. BURNS. Chromosomes of unusual
length in hybrids between two species of Nicotiana. In Chromosomes Today, Vol. 1. C D . Darlington and K.R. Lewis, Eds. Plenum Press, New York. p. 41-56. 1966. 5. and . Phenotypic and chromosomal abnormalities associated with the introduction of heterochromatin from N. otophora into N. tabacum. Genetics 56:483-502. 1967. 6. and . Enlarged euchromatic chromosomes in hybrids between N. tabacum and N. plumbaginifolia. Genetica 46:139-153. 1976. 7. GLEBA, Y.Y., R.G. BUTENKO, and K.M. SYTNIK. Fusion
of protoplasts and parasexual hybridisation in Nicotiana tabacum (L). Dokl. Akad. Nauk. Uzb. SSR. 221:1196-1198. 1975. 8. KAO, K.N. Chromosomal behaviour in somatic hybrids of soybean—Nicotiana glauca. Mol. Gen. Genet. 150:225-230. 1977. 9.
, R.A. MILLER, O.L. GAMBORG, and B.L. HARVEY.
Variation in chromosome number and structure in plant cells grown in suspension cultures. Can.}. Genet. Cytol. 12:297-301. 1970. 10. MELCHERS, G. and G. LABIB. Somatic hybridisation of
plants by fusion of protoplasts. I. Selection of light resistant hybrids of "haploid" light sensitive varieties of tobacco. Mol. Gen. Genet. 135:277-294. 1974. 11. POWER, J.B., E.M. FREARSON.C. HAYWARD, D. GEORGE, P.K. EVANS, S.F. BERRY, and E.C. COCKING. Somatic
hybridisation of Petunia hybrida and P. parodii. Nature 263: 500-502. 1976. 12. H.H. SMITH, K.N. KAO, and N.C. COMBATTI. Inter-
specific hybridization by protoplast fusion in Nicotiana. J. Hered. 67:123-128. 1976.
1. BANKS, M.S. and P.K. EVANS. A comparison of the 13. WEISS, M.C. and H. GREEN. Human-mouse hybrid isolation and culture of mesophyll protoplasts from several cell lines containing partial cell complements of human chroNicotania species and their hybrids. Plant Sci. Lett. 7:409-416. mosomes and functioning human genes. Proc. Nat. Acad. Sci. 1976. (U.S.) 58:1104-1 111. 1967.
Pinto—a new coat patterning factor in Syrian hamsters
show that pinto behaves as an autosomal recessive mutation. It is a new and separate factor showing no genetic relationship to other white-spotting factors known for this species.
C. W I L L I A M N I X O N AND MAUREEN E. C O N N E L L Y
Materials and Methods HIS REPORT describes a new coat pattern mutation in Syrian hamsters (Mesocricetus auratus auratus) T that causes large areas of white spotting on the sides and dorsum of the animal. We are calling the mutation pinto and assigning the symbol pi to it. Breeding tests
The authors are affiliated with the Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts. This research was supported in part by USPHS Grant RR 00844. Reprint requests should be addressed to Dr. Nixon, 37 Ox Bow Lane, Randolph, Massachusetts 02368. The Journal of Heredity 68:399-402. 1977.
Pinto animals first appeared in a line of golden agouti hamsters inbred to F5. In a litter of five produced by normal golden parents, there were two golden males, one golden female, and two pinto females. Eight additional pinto animals were obtained from subsequent litters of these same parents. The inbred line involved here (Line BF) is unique and merits description. Line BF, presently inbred to nine generations, originated from animals captured from the wild in Syria in 1971 and brought to the United States by Dr. Michael Murphy1. Pinto is the first distinct mutation affecting the coat to occur in any of the lines developed from these
The Journal of Heredity
400
recently caught animals. It is well-documented history that, prior to the 1971 capture and importation of 12 hamsters, all golden hamsters in captivity had originated from three littermates surviving from a litter captured in Syria in 1930. Thus, these "new" hamsters most likely contribute a greatly expanded pool of genetic material now available in this species, and many further differences between these and conventional hamsters may reasonably be expected upon further investigation. Line BF traces its origin to 6 of the original 12 feral animals (males 2, 6, and 7; females 4, 9, and 12). No unusual coat differences (from wild-type golden agouti) were noted in the line until the fifth generation of inbreeding when the two-pinto females appeared. Steps were immediately taken to preserve the mutation and at the same time to test its mode of inheritance and also possible allelism with each of the other previously described autosomal mutations for white spotting in the hamster. In addition, some linkage studies were made. In order to accomplish these goals, inbreeding of pinto animals within the BF line was continued. In addition, various outcrosses were made to conventional hamster
lines (wild-type golden agouti, piebald (s/s), dominant spot (Ds/+), white band (Ba/-), and anophthalmic white (Wh/Wh). All of these conventional hamster lines were obtained from a private colony maintained by one of us (CWN). It was not considered necessary to outcross pinto animals to sex-linked mottled white (Mo/+) once the autosomal nature of pinto had been determined. A thorough description of the autosomal white spotting factors mentioned here has been previously published by Nixon et al. 2 and all known references to these factors are listed in that paper. For the purposes of the present paper, however, Table I describes and compares the known white spotting factors in the hamster.
Results The genetic factor pinto is the sixth white spotting mutation to be found in this species (Figure 1). Phenotypically, it most closely resembles white band (Ba), an autosomal dominant factor. However, in white banded animals, white is limited to the general area across the mid-dorsum with considerable variation as to
Table I. Tabulation comparing known white spotting factors in the Syrian hamster Factor/year description published
Symbol
I. Piebald/1949
Gene effects on coat
Additional gene effects
Autosomal, recessive
Irregular white patches on dorsum, often with white forehead blaze; may have more white areas on ventrum than on wild type; ventral dark gray chest band present but may be reduced
Bone abnormalities (lighter than normal); small body size; urogenital anomalies
Inheritance
2. Mottled white/1954
Mo
Sex-linked, dominant
White patches may be present but are usually not discrete; more often, white hair is mixed in with pigmented hair
Homozygous (Mo/Mo females) and hemizygous (MolY males) condition lethal; Mol+ females often smaller than normal
3. Anophthalmic white/ 1958
Wh
Autosomal, semidominant
Whl+ (Imperial): possible sprinkling of white guard hairs on sides and dorsum; ventral fur white; dark chest band absent Wh/Wh (Blind albino); apparently, animal completely devoid of pigment; coat white
None
Eyes unpigmented (pink), usually reduced (microphthalmia), or possibly occasionally lacking (anophthalmia); hearing possibly also impaired
4. White band/1960
Ba
Autosomal, dominant
Discrete white areas present as a white band completely or incompletely encircling sides and dorsum near middle of animal; ventral fur varies from gray to entirely white
None
5. Dominant spot/ 1969
Ds
Autosomal, dominant
Irregular white patches on dorsum, often with white forehead blaze; ventral fur entirely white; ventral dark gray chest band absent
Homozygous condition (DslDs) lethal
6. Pinto/present report
pi
Autosomal, recessive
Large areas of random discrete white spotting; ventral fur white; dark gray chest band partially or wholly absent; pigmented areas of coat lighter than normal
None
401
Notes
size and distribution of the white band; in pinto animals, large areas of white occur anywhere on the sides and dorsum. Belly fur is white in both white banded and pinto animals. Another effect of the pinto gene appears to be the overall lightening of the nonwhite areas. Thus, otherwise golden agouti areas of a pinto animal are somewhat lighter than comparable areas of a nonpinto one. This basic color difference (probably a dilution effect) prevails on siblings in a mixed segregation of golden agouti and pinto animals. There is no comparable lightening of the colored areas in the case of banded animals. When golden agouti animals (noncarriers of any other known color or pattern factor) were crossed with pinto, :
FIGURE 1—A pinto mutant showing large areas of white spotting on the sides and back. There is also an overall lightening of pigmented areas, which is probably a dilution effect of the pinto gene.
Table II.
Results of crossing pinto with four other white spotting factors
Mating type 1) piebald (sis) x pinto (pi/pi) observed expected F, x F, from above observed expected (theory: 9:3:4) 2) banded (Bal+) x pinto (pilpi) observed expected F, banded x F, banded from above observed expected (theory: 3:9:4) 3) anophthalmic white (Wh/Wh) x pinto (pilpi) observed expected F, imperial x F, imperial from above observed expected (theory: 3:4:6:3) 4) dominant spot (Ds/+) x pinto (pilpi) observed expected F, dominant spot x F, dominant spot from above observed expected (theory: 3:6:1:2)
Total
Offspring phenotypes
9 agouti 9
9
a
47 agouti
5 piebald
17 pinto & piebald/pinto
68
38.8
12.9
17.2
69
5 agouti 6
7 banded 6
16 agouti
30 banded
45 pinto & banded/pinto
91
17.1
51.2
22.8
91
28 imperial 28
28 28
12 12
17 agouti
18 anophthalmic white
22 imperial
16 pinto & imperial/ pinto
73
13.69
18.25
27.38
13.69
7f
2 agouti 2.5
3 dominant spot 2.5
3 agouti
0 dominant spot
1 pinto
3 dominant spot/pinto
7
1.75
3.50
0.58
1.17
7
S
5
402
The Journal of Heredity
the F, generation, numbering well over 50 animals, was 100 percent golden agouti. Among 95 F2 animals, 71 were golden agouti and 24 were pinto. The two colors were well distributed between the sexes. This is significant support for a simple 3: 1 segregation of an autosomal recessive factor (theoretical ratio is: 71.25:23.75). In routine breeding of the present colony, pinto animals have been crossed with other pintos well over 100 times, and the results have been, without exception, 100 percent pinto offspring. Having established the mode of inheritance of pinto, it appeared desirable to determine if pinto might be allelic with any of the other white spotting factors. Thus, crosses were made between pinto animals and each of the following distinct mutant types: piebald (s/s), white band (Bal-), anophthalmic white (Wh/Wh), and dominant spot (Ds/+). A discussion follows of the results of these crosses, and they are also shown in Table II. When piebald animals were crossed with pinto (sis x pi Ipi), 9 F, offspring were all agouti. Among 69 F2 offspring, there were 47 agouti, 5 piebald, and 17 that were either pinto or piebald-pinto. As in every F2 segregation for pinto and one of the other white patterning factors, it was difficult or impossible to distinguish with any degree of certainty between pinto and pinto combined with the other patterning factor. This was due to the extensive and exceedingly variable amount of white that pinto alone imparts to different animals along with a similar effect caused by the other factor being tested. The problem was most notable and extreme in the case of white band, the pattern factor most closely resembling pinto. In the case of piebald white spotting, it will be noted in Table II that the observed number of piebald animals in F2 was far below the number expected. It is well established, however, that piebald animals have a considerably reduced viability, and it would have been surprising if the number were greater. Due to these factors, any effort to determine probabilities (by chisquare analysis) would be an exercise in futility. However, even without the full support of such statistical methods, certain conclusions can be made concerning these crosses. For instance, it can be concluded that piebald white spotting and pinto are nonallelic. It is likely, also, that the two factors are not linked since the F2 segregation gave a group of animals some of which were clearly a combination of piebald and pinto. Heterozygous white banded animals crossed with pinto (Bal+ x pi/pi) produced 12 F, offspring of which 5 were agouti and 7 white banded. Among 91 F2 offspring from banded F, parents, 16 were agouti, 30 white banded, and 45 either pinto or white banded-pinto. The difficulty experienced in separating pinto from banded-pinto has already been mentioned. This was due to the extreme variability of white areas produced by both of these factors. Indeed, it is likely that some of the heavily white banded animals were also included in the pinto, banded-pinto category. However, it can be concluded that white band and pinto are nonallelic and that the two factors are not linked since the F2 segregation showed a sizeable number of animals that were a combination of white band and pinto. The exact number of these is uncertain, of course, due to color overlap.
When anophthalmic white animals were crossed with pinto (Wh/Wh Y. pi Ipi), 28 F, offspring were all agouti imperial (Whl+ +lpi). F2 offspring numbered 73 (17 golden agouti, 18 anophthalmic white, 22 agouti imperial, and 16 pinto or imperial-pinto). Clearly, anophthalmic white and pinto are not alleles, and the two factors are not linked due to the apparent F2 independent segregation. It should be noted that the F, agouti imperial offspring (and also F2 agouti imperials) exhibited occasional small random white flecks in the coat. Although this condition had never been observed before by us in several lines of hamsters in this country, it was reported by Robinson3 (England), who noted: "An occasional individual may have small patches of white hair on the head and body." We attribute this variation in imperial animals to the action of modifying genes that are almost certain to be present. Indeed, there is considerable variation in shades of color and amounts of patterning throughout all the color varieties in hamsters that can only be attributed to such modifiers. Thus, Robinson's animals likely differed in the quantity and/or quality of modifying factors from our previously studied conventional hamsters, whereas the newly caught ones possess modifiers that allow or promote white flecking. When dominant spot was crossed with pinto (Dsl + x pi/pi), only 5 F, offspring were observed. These were 2 golden agouti and 3 dominant spot. When two F, dominant spotted animals (Ds/+ +/pi) were crossed, the 7 F2 offspring were: 3 golden agouti, 0 dominant spot, 1 pinto, and 3 dominant spot-pinto. Although numbers are small in these crosses, it would appear that pinto and dominant spot are not allelic and that they are also not linked. Lack of space and funds prevented repetition of the cross in order to obtain larger numbers.
Summary A new patterning factor is described for the Syrian golden hamster. It is called pinto (symbol pi), and it causes large random white areas to be present on the sides and dorsum, interrupting the ground color of the animal. Belly fur is white instead of grayish and there is an overall color lightening effect on self-colored areas. Pinto acts as an autosomal recessive factor. The relationship of pinto to other white patterning factors in hamsters is discussed. It is concluded that pinto is nonallelic with and not linked to any of the other autosomal white patterning factors: piebald (s), white band (Ba), anophthalmic white (Wh), and dominant spot (Ds). The remaining white patterning factor, mottled white (Mo), is sex linked and is assumed to be genetically unrelated to pinto. Literature Cited 1. MURPHY, M.R. Natural history of the Syrian golden hamster—a reconnaissance expedition. Am. Zool. 11:632. 1971. 2. NIXON, C.W.,
J.H.
BEAUMONT, and
M.E.
CONNELLY.
Gene interaction of coat patterns and colors in the Syrian hamster. J. Hered. 61:221-228. 1970. 3. ROBINSON, R. Genetics and karyology. In The Golden Hamster-Its Biology and Use in Medical Research. R.A. Hoffman, P.F. Robinson, and H. Magalhaes, Eds. Iowa State University Press, Ames. 1968.
In
Notes In the hybrid N. sylvestris x N. otophora all chromosomes are distinct on the basis of their morphology. To be able to identify each chromosome is particularly valuable, especially as chromosome loss is a property of animal somatic hybrid cells13 and in view of the indications that similar phenomenon is exhibited by plant somatic hybrid cells8 where wide crosses are involved. Even in somatic hybrid plants produced between two sexually compatible species there is evidence of chromosome loss7-11. Consequently the species combination N. sylvestris-N. otophora offers the possibility of determining which particular chromosomes are lost and of answering questions associated with the rate and direction of loss. In addition, exploitation of the heterochromatin spots in the nuclei of N. otophora2 may permit the study of problems concerned with the behavior of nuclei in fusion products. Summary The chromosomes of N. tabacum, N. sylvestris, N. otophora, and the F, hybrids N. tabacum x TV. otophora and N. sylvestris x N. otophora were assessed for their potential as cytological markers in a putative somatic hybrid cell. All acrocentric chromosomes in the cells of N. tabacum x N. otophora are attributable to either parent, but many of the metacentric and submetacentric chromosomes are not unequivocably identifiable. In contrast, in the hybrid A', sylvestris x N. otophora all chromosomes can be attributed to either parent. Literature Cited
2. -. The use of heterochromatin spot counts -andto determine ploidy levels in root tips and callus cultures of Nicotania otophora and its hybrids. Plant Sci. Lett. 7:417— 427. 1976. 3. CARLSON, P.S., H.H. SMITH and R.D. DEARING. Para-
sexual interspecific plant hybridisation. Proc. Nat. Acad. Sci. (U.S.) 69:2292-2294. 1972. 4. GERSTEL, D.U. and J.A. BURNS. Chromosomes of unusual
length in hybrids between two species of Nicotiana. In Chromosomes Today, Vol. 1. C D . Darlington and K.R. Lewis, Eds. Plenum Press, New York. p. 41-56. 1966. 5. and . Phenotypic and chromosomal abnormalities associated with the introduction of heterochromatin from N. otophora into N. tabacum. Genetics 56:483-502. 1967. 6. and . Enlarged euchromatic chromosomes in hybrids between N. tabacum and N. plumbaginifolia. Genetica 46:139-153. 1976. 7. GLEBA, Y.Y., R.G. BUTENKO, and K.M. SYTNIK. Fusion
of protoplasts and parasexual hybridisation in Nicotiana tabacum (L). Dokl. Akad. Nauk. Uzb. SSR. 221:1196-1198. 1975. 8. KAO, K.N. Chromosomal behaviour in somatic hybrids of soybean—Nicotiana glauca. Mol. Gen. Genet. 150:225-230. 1977. 9.
, R.A. MILLER, O.L. GAMBORG, and B.L. HARVEY.
Variation in chromosome number and structure in plant cells grown in suspension cultures. Can.}. Genet. Cytol. 12:297-301. 1970. 10. MELCHERS, G. and G. LABIB. Somatic hybridisation of
plants by fusion of protoplasts. I. Selection of light resistant hybrids of "haploid" light sensitive varieties of tobacco. Mol. Gen. Genet. 135:277-294. 1974. 11. POWER, J.B., E.M. FREARSON.C. HAYWARD, D. GEORGE, P.K. EVANS, S.F. BERRY, and E.C. COCKING. Somatic
hybridisation of Petunia hybrida and P. parodii. Nature 263: 500-502. 1976. 12. H.H. SMITH, K.N. KAO, and N.C. COMBATTI. Inter-
specific hybridization by protoplast fusion in Nicotiana. J. Hered. 67:123-128. 1976.
1. BANKS, M.S. and P.K. EVANS. A comparison of the 13. WEISS, M.C. and H. GREEN. Human-mouse hybrid isolation and culture of mesophyll protoplasts from several cell lines containing partial cell complements of human chroNicotania species and their hybrids. Plant Sci. Lett. 7:409-416. mosomes and functioning human genes. Proc. Nat. Acad. Sci. 1976. (U.S.) 58:1104-1 111. 1967.
Pinto—a new coat patterning factor in Syrian hamsters
show that pinto behaves as an autosomal recessive mutation. It is a new and separate factor showing no genetic relationship to other white-spotting factors known for this species.
C. W I L L I A M N I X O N AND MAUREEN E. C O N N E L L Y
Materials and Methods HIS REPORT describes a new coat pattern mutation in Syrian hamsters (Mesocricetus auratus auratus) T that causes large areas of white spotting on the sides and dorsum of the animal. We are calling the mutation pinto and assigning the symbol pi to it. Breeding tests
The authors are affiliated with the Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts. This research was supported in part by USPHS Grant RR 00844. Reprint requests should be addressed to Dr. Nixon, 37 Ox Bow Lane, Randolph, Massachusetts 02368. The Journal of Heredity 68:399-402. 1977.
Pinto animals first appeared in a line of golden agouti hamsters inbred to F5. In a litter of five produced by normal golden parents, there were two golden males, one golden female, and two pinto females. Eight additional pinto animals were obtained from subsequent litters of these same parents. The inbred line involved here (Line BF) is unique and merits description. Line BF, presently inbred to nine generations, originated from animals captured from the wild in Syria in 1971 and brought to the United States by Dr. Michael Murphy1. Pinto is the first distinct mutation affecting the coat to occur in any of the lines developed from these
The Journal of Heredity
400
recently caught animals. It is well-documented history that, prior to the 1971 capture and importation of 12 hamsters, all golden hamsters in captivity had originated from three littermates surviving from a litter captured in Syria in 1930. Thus, these "new" hamsters most likely contribute a greatly expanded pool of genetic material now available in this species, and many further differences between these and conventional hamsters may reasonably be expected upon further investigation. Line BF traces its origin to 6 of the original 12 feral animals (males 2, 6, and 7; females 4, 9, and 12). No unusual coat differences (from wild-type golden agouti) were noted in the line until the fifth generation of inbreeding when the two-pinto females appeared. Steps were immediately taken to preserve the mutation and at the same time to test its mode of inheritance and also possible allelism with each of the other previously described autosomal mutations for white spotting in the hamster. In addition, some linkage studies were made. In order to accomplish these goals, inbreeding of pinto animals within the BF line was continued. In addition, various outcrosses were made to conventional hamster
lines (wild-type golden agouti, piebald (s/s), dominant spot (Ds/+), white band (Ba/-), and anophthalmic white (Wh/Wh). All of these conventional hamster lines were obtained from a private colony maintained by one of us (CWN). It was not considered necessary to outcross pinto animals to sex-linked mottled white (Mo/+) once the autosomal nature of pinto had been determined. A thorough description of the autosomal white spotting factors mentioned here has been previously published by Nixon et al. 2 and all known references to these factors are listed in that paper. For the purposes of the present paper, however, Table I describes and compares the known white spotting factors in the hamster.
Results The genetic factor pinto is the sixth white spotting mutation to be found in this species (Figure 1). Phenotypically, it most closely resembles white band (Ba), an autosomal dominant factor. However, in white banded animals, white is limited to the general area across the mid-dorsum with considerable variation as to
Table I. Tabulation comparing known white spotting factors in the Syrian hamster Factor/year description published
Symbol
I. Piebald/1949
Gene effects on coat
Additional gene effects
Autosomal, recessive
Irregular white patches on dorsum, often with white forehead blaze; may have more white areas on ventrum than on wild type; ventral dark gray chest band present but may be reduced
Bone abnormalities (lighter than normal); small body size; urogenital anomalies
Inheritance
2. Mottled white/1954
Mo
Sex-linked, dominant
White patches may be present but are usually not discrete; more often, white hair is mixed in with pigmented hair
Homozygous (Mo/Mo females) and hemizygous (MolY males) condition lethal; Mol+ females often smaller than normal
3. Anophthalmic white/ 1958
Wh
Autosomal, semidominant
Whl+ (Imperial): possible sprinkling of white guard hairs on sides and dorsum; ventral fur white; dark chest band absent Wh/Wh (Blind albino); apparently, animal completely devoid of pigment; coat white
None
Eyes unpigmented (pink), usually reduced (microphthalmia), or possibly occasionally lacking (anophthalmia); hearing possibly also impaired
4. White band/1960
Ba
Autosomal, dominant
Discrete white areas present as a white band completely or incompletely encircling sides and dorsum near middle of animal; ventral fur varies from gray to entirely white
None
5. Dominant spot/ 1969
Ds
Autosomal, dominant
Irregular white patches on dorsum, often with white forehead blaze; ventral fur entirely white; ventral dark gray chest band absent
Homozygous condition (DslDs) lethal
6. Pinto/present report
pi
Autosomal, recessive
Large areas of random discrete white spotting; ventral fur white; dark gray chest band partially or wholly absent; pigmented areas of coat lighter than normal
None
401
Notes
size and distribution of the white band; in pinto animals, large areas of white occur anywhere on the sides and dorsum. Belly fur is white in both white banded and pinto animals. Another effect of the pinto gene appears to be the overall lightening of the nonwhite areas. Thus, otherwise golden agouti areas of a pinto animal are somewhat lighter than comparable areas of a nonpinto one. This basic color difference (probably a dilution effect) prevails on siblings in a mixed segregation of golden agouti and pinto animals. There is no comparable lightening of the colored areas in the case of banded animals. When golden agouti animals (noncarriers of any other known color or pattern factor) were crossed with pinto, :
FIGURE 1—A pinto mutant showing large areas of white spotting on the sides and back. There is also an overall lightening of pigmented areas, which is probably a dilution effect of the pinto gene.
Table II.
Results of crossing pinto with four other white spotting factors
Mating type 1) piebald (sis) x pinto (pi/pi) observed expected F, x F, from above observed expected (theory: 9:3:4) 2) banded (Bal+) x pinto (pilpi) observed expected F, banded x F, banded from above observed expected (theory: 3:9:4) 3) anophthalmic white (Wh/Wh) x pinto (pilpi) observed expected F, imperial x F, imperial from above observed expected (theory: 3:4:6:3) 4) dominant spot (Ds/+) x pinto (pilpi) observed expected F, dominant spot x F, dominant spot from above observed expected (theory: 3:6:1:2)
Total
Offspring phenotypes
9 agouti 9
9
a
47 agouti
5 piebald
17 pinto & piebald/pinto
68
38.8
12.9
17.2
69
5 agouti 6
7 banded 6
16 agouti
30 banded
45 pinto & banded/pinto
91
17.1
51.2
22.8
91
28 imperial 28
28 28
12 12
17 agouti
18 anophthalmic white
22 imperial
16 pinto & imperial/ pinto
73
13.69
18.25
27.38
13.69
7f
2 agouti 2.5
3 dominant spot 2.5
3 agouti
0 dominant spot
1 pinto
3 dominant spot/pinto
7
1.75
3.50
0.58
1.17
7
S
5
402
The Journal of Heredity
the F, generation, numbering well over 50 animals, was 100 percent golden agouti. Among 95 F2 animals, 71 were golden agouti and 24 were pinto. The two colors were well distributed between the sexes. This is significant support for a simple 3: 1 segregation of an autosomal recessive factor (theoretical ratio is: 71.25:23.75). In routine breeding of the present colony, pinto animals have been crossed with other pintos well over 100 times, and the results have been, without exception, 100 percent pinto offspring. Having established the mode of inheritance of pinto, it appeared desirable to determine if pinto might be allelic with any of the other white spotting factors. Thus, crosses were made between pinto animals and each of the following distinct mutant types: piebald (s/s), white band (Bal-), anophthalmic white (Wh/Wh), and dominant spot (Ds/+). A discussion follows of the results of these crosses, and they are also shown in Table II. When piebald animals were crossed with pinto (sis x pi Ipi), 9 F, offspring were all agouti. Among 69 F2 offspring, there were 47 agouti, 5 piebald, and 17 that were either pinto or piebald-pinto. As in every F2 segregation for pinto and one of the other white patterning factors, it was difficult or impossible to distinguish with any degree of certainty between pinto and pinto combined with the other patterning factor. This was due to the extensive and exceedingly variable amount of white that pinto alone imparts to different animals along with a similar effect caused by the other factor being tested. The problem was most notable and extreme in the case of white band, the pattern factor most closely resembling pinto. In the case of piebald white spotting, it will be noted in Table II that the observed number of piebald animals in F2 was far below the number expected. It is well established, however, that piebald animals have a considerably reduced viability, and it would have been surprising if the number were greater. Due to these factors, any effort to determine probabilities (by chisquare analysis) would be an exercise in futility. However, even without the full support of such statistical methods, certain conclusions can be made concerning these crosses. For instance, it can be concluded that piebald white spotting and pinto are nonallelic. It is likely, also, that the two factors are not linked since the F2 segregation gave a group of animals some of which were clearly a combination of piebald and pinto. Heterozygous white banded animals crossed with pinto (Bal+ x pi/pi) produced 12 F, offspring of which 5 were agouti and 7 white banded. Among 91 F2 offspring from banded F, parents, 16 were agouti, 30 white banded, and 45 either pinto or white banded-pinto. The difficulty experienced in separating pinto from banded-pinto has already been mentioned. This was due to the extreme variability of white areas produced by both of these factors. Indeed, it is likely that some of the heavily white banded animals were also included in the pinto, banded-pinto category. However, it can be concluded that white band and pinto are nonallelic and that the two factors are not linked since the F2 segregation showed a sizeable number of animals that were a combination of white band and pinto. The exact number of these is uncertain, of course, due to color overlap.
When anophthalmic white animals were crossed with pinto (Wh/Wh Y. pi Ipi), 28 F, offspring were all agouti imperial (Whl+ +lpi). F2 offspring numbered 73 (17 golden agouti, 18 anophthalmic white, 22 agouti imperial, and 16 pinto or imperial-pinto). Clearly, anophthalmic white and pinto are not alleles, and the two factors are not linked due to the apparent F2 independent segregation. It should be noted that the F, agouti imperial offspring (and also F2 agouti imperials) exhibited occasional small random white flecks in the coat. Although this condition had never been observed before by us in several lines of hamsters in this country, it was reported by Robinson3 (England), who noted: "An occasional individual may have small patches of white hair on the head and body." We attribute this variation in imperial animals to the action of modifying genes that are almost certain to be present. Indeed, there is considerable variation in shades of color and amounts of patterning throughout all the color varieties in hamsters that can only be attributed to such modifiers. Thus, Robinson's animals likely differed in the quantity and/or quality of modifying factors from our previously studied conventional hamsters, whereas the newly caught ones possess modifiers that allow or promote white flecking. When dominant spot was crossed with pinto (Dsl + x pi/pi), only 5 F, offspring were observed. These were 2 golden agouti and 3 dominant spot. When two F, dominant spotted animals (Ds/+ +/pi) were crossed, the 7 F2 offspring were: 3 golden agouti, 0 dominant spot, 1 pinto, and 3 dominant spot-pinto. Although numbers are small in these crosses, it would appear that pinto and dominant spot are not allelic and that they are also not linked. Lack of space and funds prevented repetition of the cross in order to obtain larger numbers.
Summary A new patterning factor is described for the Syrian golden hamster. It is called pinto (symbol pi), and it causes large random white areas to be present on the sides and dorsum, interrupting the ground color of the animal. Belly fur is white instead of grayish and there is an overall color lightening effect on self-colored areas. Pinto acts as an autosomal recessive factor. The relationship of pinto to other white patterning factors in hamsters is discussed. It is concluded that pinto is nonallelic with and not linked to any of the other autosomal white patterning factors: piebald (s), white band (Ba), anophthalmic white (Wh), and dominant spot (Ds). The remaining white patterning factor, mottled white (Mo), is sex linked and is assumed to be genetically unrelated to pinto. Literature Cited 1. MURPHY, M.R. Natural history of the Syrian golden hamster—a reconnaissance expedition. Am. Zool. 11:632. 1971. 2. NIXON, C.W.,
J.H.
BEAUMONT, and
M.E.
CONNELLY.
Gene interaction of coat patterns and colors in the Syrian hamster. J. Hered. 61:221-228. 1970. 3. ROBINSON, R. Genetics and karyology. In The Golden Hamster-Its Biology and Use in Medical Research. R.A. Hoffman, P.F. Robinson, and H. Magalhaes, Eds. Iowa State University Press, Ames. 1968.
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