The Hypostatic Genotype of the Recessive White Prat Breed of Chickens

Transcription

1 The Hypostatic Genotype of the Recessive White Prat Breed of Chickens J. L. CAMPO Area de Genética Animal, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Apartado 8111, Madrid, Spain ABSTRACT The genetics of the plumage color of the White Prat breed of chicken was studied. Results of crosses between the White Prat breed and Recessive Wheaten (ey/ey) tester line, and Buff Prat (ewh/ewh Co/ Co) or Castellana (E/E) breeds, suggested that the former carries the buttercup allele (ebc) at the E-locus, the columbian restriction gene (Co), and the autosomal recessive white (c) gene. Heterozygous Co/co+ in the presence of ebc resulted in a modified stripe pattern in the chick down. The ground color was very dark tan, whereas the light back stripes and the broken head stripe were similar to those of buttercup chicks. Adults were typical buff columbian with considerable black markings on the feathers. The homozygous ebc/ebc Co/ Co produced chicks with a black back and a brown head, similar to those previously described for the interaction between Co and the brown (eb) allele. The presence of the recessive white gene masked unexpected genetic variation at the E-locus in the Prat breed, the Buff variety carrying the dominant wheaten (ewh) instead of the buttercup allele. The sex-linked gold (s+) allele was the most frequent in the White Prat variety. The silver (S), sex-linked barring (B), blue (Bl), and possibly dominant white (I) alleles also were present at low frequencies. (Key words: plumage color, recessive white, hypostatic variation, buttercup allele, columbian interaction) 1997 Poultry Science 76: INTRODUCTION There are four kinds of white plumage in the fowl. One of these is produced by the dominant white (I) gene, and it is a breed characteristic of White Leghorns. The three remaining whites are recessive. Recessive white (c) is the most common form of white plumage that is inherited as a recessive mutation, and it is a varietal characteristic of White Plymouth Rock, White Wyandotte, and other breeds. The dominant and recessive white mutations were some of the earliest animal traits to be studied following the rediscovery of Mendel s laws (for review, see Smyth, 1990). In addition to full color (C+) and c, there are two other alleles at the c-locus: autosomal albinism (ca; Brumbaugh et al., 1983) and white with dark red pigmented eyes (cre; Smyth et al., 1986). Finally, there is a distinct sex-linked albinism (sal; Mueller and Hutt, 1941) at the S-locus, which results in essentially white plumage with partial pigmentation. The sal on an extended black background is a light greyish tan in both chick down and adult plumage, whereas on a red columbian background, the down is creamy and adult feathers have red pigment. Although C+ is usually considered to be completely dominant to c, Carefoot (1979) observed dilution effects on both Received for publication May 6, Accepted for publication October 8, pheomelanin and eumelanin in C+/c heterozygotes, in a study with Partridge Wyandotte Bantams. The two forms of white plumage (dominant, I, and recessive, c) are epistatic to most other colors and patterns, and the phenotypic uniformity of a white breed may conceal a considerable amount of diversity at loci affecting plumage color and patterns (Quinn, 1936; Jaap, 1943; Jeffrey, 1947; Jerome and Cavers, 1952; Cock, 1956). The c locus in general appears to inhibit pheomelanin more effectively than it does eumelanin; in contrast, I is a relatively ineffective inhibitor of pheomelanin. Results by Quinn (1936) and Jeffrey (1947) appeared to indicate more segregation at E, B, and S loci for c/c than for I/I lines, suggesting that c needs less assistance than I to produce white plumage. Although recessive white birds may carry either S or s+ (Quinn, 1936; Jeffrey, 1947), silver is an important part of the genotype of dominant whites. Crosses between recessive white and colored breeds of poultry may give unexpected results, especially when the genotype of the white breed is unknown. The hypostatic genotypes that are associated with down color variations in c/c chicks have not been clarified. The extended black (E) allele appears to be present when the downs are greyish (Jaap, 1943; Jeffrey, 1947); however, data by Jerome and Cavers (1952) did not support the need for E to produce smoky down. Less is known about the red-tinted downs. Adult plumages of c locus mutants are typically white, even though the chick down may have gray or red tints of melanin. 432

2 GENETICS OF WHITE PRAT PLUMAGE 433 The White Prat is the only population with white plumage that is maintained in a conservation program of Spanish genetic resources started in 1975 (Campo and Orozco, 1982). Making sex-linked crosses involving this white breed requires knowledge of its genetic background. It seems that the White Cochin breed was utilized in the original formation of the White Prat, and the White Cochin carries the recessive white (c) gene (Somes, 1988). On the other hand, the White Minorca breed, which is historically and geographically related to the White Prat, also seems to be c/c (Smyth, 1990), although dominant white may be present in this and other recessive white breeds. Somes (1988) says that the White Minorca is I/I, E/E, or ey/ey. The Prat breed comes from the area around Barcelona. It was a traditional productive breed used in Spain before the introduction of the commercial hybrids; its phenotypic standard was defined in 1916 (Corominas, 1953). Buff and White are the recognized varieties of the Prat, Buff being the most popular. The Buff Prat ( Catalana del Prat Leonada ) was admitted to the American Standard of Perfection in 1949 (American Poultry Association, 1983). Feathers are all white in the White Prat, and its chick down is yellow. Eye color is reddish bay in both varieties, and shank color is dark slaty blue, dermal melanin being neither eliminated nor diluted by the white plumage color. Dermal melanin in the shanks is generally expressed in day-old chicks. The purpose of the present study was to conduct a genetic analysis of the plumage color of the White Prat breed of chickens. A test to detect the presence of Co in the chick down is also presented as a by-product from the experiment. MATERIALS AND METHODS Birds from the White Prat variety were crossed with the Buff Prat variety, the Castellana (a different Spanish breed), and a Recessive Wheaten tester line obtained from J. R. Smyth, Jr. (University of Massachusetts, Amherst, MA 01002). All of these populations are maintained at the Experimental Station of El Encín (28806 Alcalá de Henares, Madrid). Adults in the Buff Prat variety have ginger red plumage with a columbian restricted pattern, the black feathers appearing on the tail and wings. The basic color genotype of these birds is due to an interaction between the dominant wheaten (ewh) allele and the columbian restriction (Co) gene (Campo and Orozco, 1984). Its usual chick down is orange buff. The Castellana breed is all black (E/E; Campo and Orozco, 1984). The chicks are black with yellowish or white ventral surfaces and wing tips. The melanotic gene (Ml) may have been incorporated by poultry fanciers into the Castellana to ensure completely black plumage (Campo and Orozco, 1986), and may be present in the breed at unknown frequency. Adult males of the Recessive Wheaten tester line have black-breasted red plumage, whereas the females are salmon-brown in color with darker pigmentation in the hackle, wings, and tail (Brumbaugh and Hollander, 1966). The ey/ey chicks are cream-colored with a small head spot or narrow dark back stripes. Three different groups of crosses were made. The first was a cross between White Prat males and Recessive Wheaten females. The F 1 generation was produced from 10 separate pens, each with 1 male and 3 females, whereas the F 2 generation was obtained from three matings each utilizing 1 F 1 male and 10 F 1 females. The second group of matings originated from crosses between 1 Buff Prat male and 10 White Prat females. Four pens each with 1 F 1 male and 10 F 1 females were used to produce an F 2 generation. The reciprocal F 1 cross between a White Prat male and 10 Buff Prat females was also established in an attempt to analyze possible sex-linked effects for white. The third group of matings originated from 10 separate pens, each with 1 White Prat male and 3 Castellana females, followed by an F 2 generation produced from four matings each utilizing 1 male and 10 females. The reciprocal F 1 mating was made in a breeding pen with 3 Castellana males and 30 White Prat females, to widen the parental basis of an F 1 using the white population as male parent, and to increase the possibility of detecting segregation. Both 1-d and 12-wk plumage color descriptions were obtained from the resulting F 1 and F 2 progeny. Statistical analyses using chi-square (Snedecor and Cochran, 1980) were based on 12-wk. RESULTS Mating of White Prat with Recessive Wheaten Eight of the males produced 65 chicks with very dark ground color and a definite stripe pattern, the light parallel back stripes being irregular and wide, and the head stripe being broken. The phenotype of the adults was buff columbian restricted. The males had a great degree of black tipping on the feathers, whereas the females showed considerable stippling, particularly on the back region. The 378 F 2 adults (Table 1) were classified as buff columbian, white, buttercup, or wheaten at a ratio that approximated 36:16:9:3 (P > 0.1). Buff columbian males showed varying degrees of black tipping, whereas columbian females showed frequently considerable black stippling. Some of the white adult females had red pigment on the feathers. Adult males of both buttercup and wheaten had identical black-breasted red plumage; adult buttercup females showed a similar stippling on the body and breast feathers, whereas adult wheaten females had black back stippling. As chicks, buff columbian adults were striped very dark tan, orange buff with or without an ashy back coloration, or grayish-black with a brown head. The adults showing the maximum degrees of black tipping (males) or stippling (females) had striped dark tan chicks. Chick color in white birds was yellow or cream; females classified as white with red

3 434 CAMPO Obtained TABLE 1. Segregation in the F 2 generation from the mating of White Prat Recessive Wheaten (e y /e y co + /co + C + /C + ) 1 Possible genotypes Buff columbian e bc / Co/ C + / e y /e y Co/ C + / White e bc / Co/ c/c e bc / co + /co + c/c e y /e y Co/ c/c e y /e y co + /co + c/c Buttercup e bc / co + /co + C + / Wheaten e y /e y co + /co + C + / Based on the genotype of the White Prat being e bc /e bc Co/Co c/c with an expected proportion of 36:16:9:3. 2x 2 = 2.60; P > 0.1. feathers were cream as chicks. Chick down of the buttercup birds was light tan with irregular and wide parallel back stripes and broken head stripe. Chick down of the wheaten birds was cream. Two White Prat males also produced some F 1 chicks with yellow down, and some F 1 chicks with orange buff down; as adults, they were silver columbian and buff columbian, respectively. These data suggest that the variant White Prat males were segregating for the sexlinked silver and gold alleles and carried a wheaten allele. Mating of Buff Prat and White Prat The Buff Prat White Prat cross resulted in 61 buff columbian birds. Most of them had a phenotype similar to that of the Buff Prat; some males showed black tipping on the feathers, whereas some females had diverse degrees of back stippling. As chicks, they were generally orange buff, with the addition in some of an ashy back coloration or a black head spot; chick color in birds with black markings was nearly black with a brown head. Similar results were obtained in the progeny of the reciprocal mating (White Prat Buff Prat); this cross resulted in 64 buff columbian birds, most of them having orange buff chick down. Adults of the F 2 generation from the Buff Prat White Prat cross (Table 2) were classified as buff columbian or white, with the segregation of the 330 F 2 progeny closely fitting a 3:1 ratio (P > 0.5). Some of the 117 columbian males and 129 columbian females showed black markings and black stippling on the feathers. Most of the buff columbian adults were orange buff as chicks, or orange buff with an ashy back; chick color of columbian birds showing black markings was grayish-buff or nearly black with a brown head. Chick color of birds classified as white was yellow. A White Prat female also produced some F 1 chicks with cream down; as adults they were buff columbian with white feathers on the tail and wings. These data suggest that the variant White Prat female was carrying the I mutation, and offspring were white-tailed red I/i+, as the pheomelanic pigment is apparent on a heterozygous dominant white columbian background, whereas the eumelanic pigment is not. Mating of White Prat with Castellana Most of the 87 F 1 birds had completely black plumage; the remaining birds were black with red pigment present on some feathers. As chicks, they were black with white ventral surfaces, some of them showing a reddish color on the face or a chocolate coloration with a brown head. Similar results were obtained in the 84 F 1 birds from the reciprocal mating (Castellana White Prat), most of them being all black. TABLE 2. Segregation in the F 2 generation from the mating of Buff Prat (e Wh /e Wh Co/Co C + /C + ) White Prat 1 Obtained Possible genotypes Buff columbian e Wh / Co/Co C + / e bc /e bc Co/Co C + / White e Wh / Co/Co c/c e bc /e bc Co/Co c/c 1Based on the genotype of the White Prat being e bc /e bc Co/Co c/c with an expected proportion of 3:1. 2x 2 = ; P > 0.5.

4 Obtained GENETICS OF WHITE PRAT PLUMAGE 435 TABLE 3. Segregation in the F 2 generation from the mating of White Prat Castellana (E/E co + /co + C + /C + ) 1 Possible genotypes Black E/ Co/ C + / E/ co + /co + C + / White E/ Co/ c/c E/ co + /co + c/c e bc /e bc Co/ c/c e bc /e bc co + /co + c/c Buff columbian e bc /e bc Co/ C + / Buttercup e bc /e bc co + /co + C + / Based on the genotype of the White Prat being e bc /e bc Co/Co c/c with an expected proportion of 36:16:9:3. 2x 2 = 3.49; P > 0.1. Table 3 shows the results obtained in the 389 birds from the F 2 generation of the mating of White Prat Castellana. Black, white, buff columbian, and buttercup approximated an expected 36:16:9:3 ratio (P > 0.1). Most of the black adult females had completely black plumage, whereas about one half of the black males showed red feathers in hackle, saddle and wing-bows. Most of the white birds were similar to the White Prat breed; one of the adult males showed red pigment in saddle and wingbows, and one of the adult females showed red pigment in breast and shoulders. The buff columbian males had diverse degrees of black markings, some of them being similar to a melanotic columbian phenotype; the buff columbian females had diverse degrees of black stippling on the feathers. The buttercup adult males were blackbreasted red, and the buttercup females showed a definite stippling in the body and breast feathers. As chicks, black birds were black, black with a red face, or chocolate-black with a brown head. White birds had generally yellow chicks, some of them being grayish or bluish; however, none showed black or blue markings in the adult plumage. Chick down in the male classified as white with red feathers, was cream with two lateral yellow back stripes. Buff columbian chicks had a buttercup stripped pattern with a dark tan ground color, or were nearly black with a brown head. Chicks classified as buttercup were stripped with a typical light ground color. A White Prat male also produced some F 1 chicks with black down and a white head spot, and some F 1 chicks with dark blue down; as adults they were black barred, with some red feathers, and blue, respectively. These data seem to suggest that the variant White Prat male was carrying the sex-linked barring gene and the blue mutation. DISCUSSION Data from the cross between the White Prat and the Recessive Wheaten tester line indicate that the White Prat breed carries the buttercup allele (ebc) at the E- locus. This fact was further verified by the cross between the White Prat and the Castellana breeds. The buttercup chicks, reported previously by Smyth et al. (1980), are similar to those found in the F 2 generation of the White Prat Recessive Wheaten cross and in the mating of White Prat Castellana. The adult primary pattern in the presence of ebc closely resembles that found in the F 2 generation from both crosses. Results of these matings suggest that a columbian mutation (Co), is carried by the White Prat breed. If a columbian gene had not been involved, the F 2 segregation between the White Prat and the Recessive Wheaten tester line would not have been included columbian. Furthermore, if a columbian gene had not been carried by the White Prat, the F 2 segregation of the Buff Prat White Prat varieties would have included wheaten and buttercup individuals among the nonwhite. The three crosses have shown that the white gene in the Prat is the recessive one (c), as the F 2 had proportions of 3 colored:1 white. Reciprocal crosses between White Prat males and Buff Prat females yield comparable results to those of Buff Prat White Prat, indicating that the white locus was not sex-linked. The same fact was observed in the reciprocal cross between the Castellana and White Prat breeds in relation to its direct cross. The presence of the recessive white (c) allele in the White Prat genotype masked unexpected genetic variation at the E-locus in the Prat breed, as the previously defined genotype of the Buff Prat variety (Campo and Orozco, 1984) carried the dominant wheaten allele (ewh), instead the buttercup allele (ebc) found in the white variety, and the former should be the allele carried by the white variety if all White Prats were created from the buff variety. The presence of a wheaten-type allele (dominant or recessive) segregating at low frequency is suggested by the two variant White Prat males tested in the mating with the Recessive Wheaten line. Brumbaugh and Hollander (1966) reported a Buff Minorca population to be heterozygous for the buttercup and recessive wheaten (ey) alleles. The buttercup allele derives from the Sicilian Buttercup breed, and these two Mediterranean isles are historically related to the region of origin of the Prat breed. The recessive white varieties previously reported in the literature all carried the extended black (E) allele, the only exception being the strain of

5 436 White Plymouth Rock described by Jerome and Cavers (1952). The results of all three types of crosses indicate that the recessive white gene is an effective inhibitor of pheomelanin, either on the chick down or adult plumage. Only a few adults from the White Prat Recessive Wheaten and White Prat Castellana crosses showed red pigment on the feathers and a cream color on the chick down; neither adults nor chicks from the Buff Prat White Prat mating had pheomelanin on their. The white plumage of some adult males in the White Prat variety exhibits a cream color on the hackle, saddle, and wing-bows as they increase in age, particularly after 2 yr (unpublished results), suggesting that the inhibition of pheomelanin by the recessive white allele can be reduced in older birds. The cross of the White Prat with the Castellana also showed that c/c inhibits eumelanin as effectively as it does pheomelanin. White birds showed no black markings on their adult plumage. Data from the White Prat Castellana mating support the hypothesis that the extended black allele (E) is necessary in order for gray or smokiness to be present in the c/c chick down (Jaap, 1943; Jeffrey, 1947). However, fewer than expected yellow chicks with gray color were observed; three quarters of the white birds should be homozygous or heterozygous for E. The expected proportion of white birds not carrying the columbian restriction gene (3/16) fits better the observed number, suggesting that only the E/- co+/co+ genotype allows gray color to appear in the down. No greyish yellow chicks were obtained in the White Prat Recessive Wheaten or Buff Prat crosses. Breeders of the White Prat may have selected against the extended black allele (E), because uniform down color would be useful as an aid in merchandising the chicks. The ebc allele provides a test to detect the presence of the columbian gene (Co) in the chick down; heterozygous Co in the presence of ebc results in a modified stripe pattern, whereby the ground color is very dark tan; the light back stripes and the broken head stripe are similar to those of buttercup chicks. Adults are typical buff columbian restricted with considerable black markings on the feathers. These chicks were obtained in the White Prat Recessive Wheaten and White Prat Castellana matings, but not in the Buff Prat White Prat cross, suggesting that homozygous Co does not result in a striped pattern on buttercup chicks. The chicks with black back and brown head, being presumably homozygous Co, are similar to those reported for the interaction between Co and eb genes (Smyth, 1976). Up to now, the best test to detect the presence of Co in a genetic background was the interaction between the Co and e+ alleles in a female adult plumage; the columbian gene produces adult e+/e+ females with orange-buff rather than salmon coloration on the breast and plentiful dorsal stippling (Malone and Smyth, 1979). CAMPO REFERENCES American Poultry Association, American Standard of Perfection. American Poultry Association, Inc., Troy, NY. Brumbaugh, J. A., and W. F. Hollander, Genetics of buff and related color patterns in the fowl. Poultry Sci. 45: Brumbaugh, J. A., T. W. Bargar, and W. S. Oetting, A new allele at the C pigment locus in the fowl. J. Hered. 74: Campo, J. L., and F. Orozco, Conservation and genetical study of Spanish chicken breeds (6). Pages in: Proceedings of the 2nd World Congress on Genetics Applied to Livestock Production, Madrid, Spain. Campo, J. L., and F. Orozco, A genetic study of the buff columbian color pattern in Prat chickens. J. Hered. 75: Campo, J. 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