Studies of the Pirouette Mutation

Studies of the Pirouette Mutation

Studies of the Pirouette Mutation. 1. Lack of Linkage Association with Marked Regions of Chromosomes 1 and 2 1 J. J. BITGOOD,2 E. P. EUTSLER,2 and M. ...

212KB Sizes 0 Downloads 77 Views

Studies of the Pirouette Mutation. 1. Lack of Linkage Association with Marked Regions of Chromosomes 1 and 2 1 J. J. BITGOOD,2 E. P. EUTSLER,2 and M. P. WALLACE3 Departments of Poultry Science and Wildlife Ecology University of Wisconsin-Madison, Madison, Wisconsin 53706 (Received for publication February 9, 1985)

1987 Poultry Science 6 6 : 3 8 - 4 0 INTRODUCTION

this inversion, the individual will exhibit the shankless (shl) phenotype (Langhorst and Fechheimer, 1985). This line is useful for genetic linkage studies of chromosome 2 because a cellular marker (the inversion) is available to identify heterozygous carriers, and the phenotypic marker, shl, identifies individuals that are homozygous for the inversion. The results obtained from these test matings indicate that the pir locus is not located in specific regions of chromosomes 1 and 2.

The pirouette mutation (pir) in the chicken (McGibbon, 1974) is a single gene, autosomal recessive, neurological mutation. It is evident at hatch time and throughout the life of the individual. It is characterized by whirling about (pirouetting) for a short time (less than 10 sec). Affected individuals will also exhibit a "stargazing" posture for varying periods, particularly when stimulated, such as by the presence of a caretaker or a sudden noise. Day-old chicks also display varying degrees of tremulous head movement. In spite of this, the affected chicks hatch as well as unaffected sibs. Data to support this will be presented in this paper. The pir locus has not been assigned to any linkage group. Test matings were undertaken to determine if any measurable linkage existed between pir and four other markers. Two of these markers, naked neck (Na) and tardy feathering (f), have been assigned to chromosome 1 (linkage group III) in the chicken (Somes, 1984). The third marker was the MN t(Z;l) chromosome rearrangement (Wang, 1978). The fourth marker used was the OH inv(2), a pericentric inversion on chromosome 2 (Wooster et al., 1977). When an individual is homozygous for

MATERIALS AND METHODS

A series of matings were conducted to test possible linkage relationships between pir and four other markers: Na, t, the chromosome rearrangements MN t(Z;l), and the OH inv(2). The shl mutation, associated with the OH inv(2), was used as a marker in one test. Initially, P/r + /Pir + males carrying the trait to be tested were mated with pirlpir females in single bird cages. Artificial insemination was used to obtain F,s for testing. The loci of interest were therefore in repulsion in all test matings. Na and / were tested using only intercross matings. The two chromosome rearrangements were tested using both backcross and intercross matings. The expression of all phenotypic markers used in this study is readily apparent at hatch. The phenotypes of all chicks were recorded at Day 1. Feather pulp from day-old chicks obtained from matings that used chromosome markers was processed as previously described (Bitgood, 1985). Data analyses were conducted following the procedures described by Green (1963).

'Supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison. 2 Department of Poultry Science. department of Wildlife Ecology. Current address: Greater Los Angeles Zoo Association, 5333 Zoo Drive, Los Angeles, CA 90027.

38

Downloaded from http://ps.oxfordjournals.org/ at UNIVERSITY OF ARIZONA on May 31, 2015

ABSTRACT The pirouette mutation was tested for possible genetic linkage with naked neck, tardy feathering, the MN t(Z;l) chromosome rearrangement, all assigned to distinctly different regions of Chromosome 1, and the OH inv(2) chromosome rearrangement and shankless (associated with the OH inv(2) rearrangement). No linkage associations were found in any of these tests. This eliminates specific regions of Chromosomes 1 and 2 as possible locations for the pirouette mutation. (Key words: pirouette, naked neck, tardy feathering, chromosome rearrangements, linkages)

PIROUETTE LINKAGE STUDIES TABLE 1. Tests for linkage between pirouette (pir) and the MN t(Z;l) (Trans)

Backcross mating Gamete type Trans-P;>+ Normal-pir Normal-PjV+ Trans-p!>

21 25 22 34 102

Single backcross Trans, pir intercrossed Gamete type

n

Trans-Pi>+ Normal-pir Normal-PiV+ Transmit-

32 10 34 10 86

39

TABLE 3. Test for linkage between pirouette (pir) and naked neck (Na) Gamete type

Chi-square

Na-Pir+ na+-Pir Na-pir na+-pir

160 61 42 23 286

X 2 Na = 2.91 X2 Pir = .788 X 2 L= 1.30

X2 Trans = .047 X 2 Pir= .140 X2L = .016

X2 Trans = .627 X2Pir = 2.510 X2L = .980

Combined Chi-square for linkage = .876 1 1 Information from the two types of matings consolidated and analyzed as described by Green (1963).

RESULTS AND DISCUSSION

Table 1 presents the results of the backcross and intercross matings between pir and the MN t(Z;l). There is no indication of linkage in either mating. Green (1963) outlines procedures for consolidation and analysis of results from different types of test matings. In these matings consolidation of the results to test greater numbers still produced a nonsignificant Chi-square of .876 for linkage. The MN t(Z;l) is linked by six map units to pea comb (P) and is on the proximal portion of the short arm of Chromosome 1 (Bitgood et al., 1980). The results in Table 1 indicate that pir is not closely linked to the MN t(Z;l) and thus also not to P. This eliminates this region of Chromosome 1 as a site for this locus. Table 2 indicates that no measurable linkage exists between pir and t. Munro and McGibbon (cited by Etches and Hawes, 1973) suggested

linkage of 41 map units between P and t. Warren (1949) reported 125 recombinants among 287 individuals (43%) in a test between P and t. An intercross mating to test this further has also shown 41% recombination (P<.005) (unpublished observations). If these results are substantiated, pir does not lie within measurable distance of the region of Chromosome 1 delineated by P and t, The results of the pir-Na test mating are in Table 3. No indication of linkage is apparent with 286 individuals tested. If Na is located on Chromosome 1, as shown on the current map (Somes, 1984), the studies reported here indicate pir may be on a different chromosome. The three markers on Chromosome 1 that were used, the MN t(Z;l), t and Na, span a good distance on this chromosome. Table 4 presents the results of the backcross and intercross matings between pir and the OH

TABLE 4. Tests for linkage between pirouette and the OH inv(2)/shankless (shl) Backcross mating Gamete type inv-ft>+ Normal-pir Normal-fty*" inv-pir

TABLE 2. Test for linkage between pirouette (pir) and tardy feathering (t)

(pir)

Intercrossi mating

n 31 29 23 24

Gamete type

n

Shl+-Pir+ Shl+-pir shl-Pir+ shl-pir

38 13 7 4

107

62

Chi-square Chi-square

Gamete type T+-Pir+ t-Pir+ T+-pir t-pir

83 29 22 14 148

X2 Tardy = 1,297 X 2 Pir= .036 X 2 L = 2.35

X2 inv = .084 X2 Pir = .009 X2L = 1.579

X 2 Shl= 1.74 X 2 Pir= .194 X 2 L = .351

Combined Chi -squiire for linkage = .796' 1 Information from the two types of matings consolidated and analyzed as described by Green (1963).

Downloaded from http://ps.oxfordjournals.org/ at UNIVERSITY OF ARIZONA on May 31, 2015

Chi-square

40

BITGOODETAL. TABLE 5. Segregation of pirouette in the two types ofmatings Backcross

Pir+ pir n

Intercross

Obs.'

Exp.

Obs.

Exp.

97 112 209

104.5 104.5

444 138 582

436.5 145.5

Chi square for segregation = 2.69

.97

inv(2)M/ matings. In the backcross mating, F ; males of genotype N,pir/l, Pir+ (N = standard chromosome; I = inv(2)) were backcrossed to N, pir/N, pir females. Chromosomes of the chicks were analyzed to determine presence or absence of the inversion. In the intercross matings, the Fx parents were also N, pir/l, Pir+. The F 2 progeny were scored for presence or absence of pir and shl, as the shl phenotype is a marker for homozygosity of the inversion (Langhorst and Fechheimer, 1985). No significant linkage relationships were noted in either test, and a combined Chi-square also indicated independent segregation. Kaelbling and Fechheimer (1985) examined the synaptonemal complexes formed by males heterozygous for this pericentric inversion in Chromosome 2. They found a high frequency of nonhomologous pairing and unpaired loops in the region of the chromosome that was involved in the inversion, suggesting that there is no recombination occurring within the inverted segment. The results in Table 4 indicate that the pir locus is not in the region of Chromosome 2, which is involved in this inversion. Few, if any, recombinants would be expected for any loci that lie in this chromosome segment.

REFERENCES Bitgood, J. J., 1985. Additional linkage relationships within the Z chromosome of the chicken. Poultry Sci. 64:2234-2238. Bitgood, J. J., R. N. Shoffner, J. S. Otis, andW. E. Briles, 1980. Mapping of the genes for pea comb, blue egg, barring, silver, and blood groups A, E, H, and P in the domestic fowl. Poultry Sci. 59:1686-1693. Etches, R. J., and R. O. Hawes, 1973. A summary of linkage relationships and a revised linkage map of the chicken. Can. J. Genet. Cytol. 15:533-570. Green, M. C , 1963. Methods for testing linkage. Pages 56-82 in: Methodology in Mammalian Genetics. W. J. Burdette, ed. Holden-Day, Inc., San Francisco, CA. Kaelbling, M., and N. S. Fechheimer, 1985. Synaptonemal complex analysis of a pericentric inversion in chromosome 2 of domestic fowl, Gallus domesticus. Cytogenet. Cell Genet. 39:82-86. Langhorst, L. J., and N. S. Fechheimer, 1985. Shankless, a new mutation on chromosome 2 in the chicken. J. Hered. 76:182-186. McGibbon, W. H., 1974. Pirouette: A behavioral mutant in the domestic fowl. J. Hered. 65:124-126. Somes, R. G., 1984. Linked loci of the chicken - Gallus gallus (G. domesticus). Genet. Maps 3:465^173. Wang, N., 1978. Induction of chromosomal structural and numerical changes in the chicken (Gallus domesticus). Ph.D. Thesis, Univ. Minnesota. Warren, D. C , 1949. Linkage relations of autosomal factors in the fowl. Genetcs 34:333-350. Wooster, W. E., N. S. Fechheimer, and R. G. Jaap, 1977. Structural rearrangements of chromosomes in the domestic chicken: Experimental production by X-irradiation of spermatozoa. Can. J. Genet. Cytol. 19:437-446.

Downloaded from http://ps.oxfordjournals.org/ at UNIVERSITY OF ARIZONA on May 31, 2015

'Obs. = observed, Exp. = expected, based on 1:1 segregation.

Table 5 substantiates the premise that pir chicks do not show reduced hatchability. Results from the different backcross matings and the intercross matings were pooled into their respective groupings and subjected to Chi-square analysis. The numbers of pir and normal progeny from each of the two types of matings show no significant deviations from expected. This also indicates that pir is an ideal mutation to use in linkage studies, as it shows complete penetrance and can be identified at hatch time.