A new recessive ametapodia mutation in the chicken (Gallus domesticus).

An apparently new mutation that is associated with abnormal limb development appeared in a strain of Light Brown Leghorn chickens. Mutants are characterized by the complete absence of the tarsometatarsals, while severely hypoplastic development of the metacarpals is also present. The phenotype of the new mutant (ametapodia-2) closely resembles ametapodia-1, described in 1967, but ametapodia-2 is inherited as an autosomal recessive (AMET*A), while ametapodia-1 was associated with an incompletely dominant gene (MP*A). Only heterozygous ametapodia-1 (MP*N/MP*A) were viable and able to reproduce, while homozygous ametapodia-2 mutants do not normally survive beyond 2-4 days of age. The shankless mutation (SHL*S) also reduces development of the metatarsal and metacarpal bones and has been shown to be associated with a pericentric inversion of chromosome 2. No obvious cytologic abnormality was apparent in ametapodia-2 birds, and offspring of a cross between AMET*A carriers and shankless birds were normal, indicating that the two mutations are not alleles. Ametapodia-1 (MP*A) was found to be linked to the rose comb locus (R) by 16 crossover units. Linkage test matings between AMET*A and (R*R) showed independent segregation, strongly suggesting that the mutation occurred at a relatively distant locus and therefore is probably not allelic to MP*A.

Further tests for genetic linkages of three morphological traits, three blood groups, and break points of two chromosome translocations on chromosome one in the chicken.

Two matings were conducted to further test the locations of the pea comb (P*), blue egg shell color (O*), and tardy feathering (T*) loci. In each mating a different chromosome rearrangement break point (R(B)) was tested against the three loci. Independent segregation was noted between the traits and the R(B) when the R(B) was on the long arm of chromosome 1. Significant linkage was noted when an R(B) on the short arm was tested against the three markers, indicating that the loci for P*, O*, and T* are on the short arm. Three blood group loci, EAD*, EAI*, and EAP*, were simultaneously tested against the short arm R(B). Independent segregation was noted in each instance, indicating that these blood group loci are not on the short arm of chromosome 1.

International system for standardized avian karyotypes (ISSAK): standardized banded karyotypes of the domestic fowl (Gallus domesticus).

The chicken genetic map is becoming very detailed. The genetic and physical maps need to be integrated in more detail. It is important to have a consensus banded karotype to permit this integration. An international committee met to develop a karyotype for the eight largest chromosomes and the Z and W chromosomes of the domestic fowl (Gallus domesticus). This map is presented in this report.

Linkage relationships of the Z-linked silver, slow feathering, and pop-eye loci.

A three-point genetic linkage test was conducted to establish linear relationships of the Z-linked loci pop-eye (POP*), silver (S*), and rate of feathering (K*). Linkage values obtained in a back cross were POP* - 17.8 - S* - 2.4 - K* (n = 169). The POP* - K* distance was 19.0, supporting this linear order. The data support the previous assignment of POP* to the short arm of the Z chromosome. Based on previous reports, of the three loci studied, POP* is closest to the centromere.

Novel chromosomal insertional translocation in chicken uncovered by double color FISH.

A novel insertion 78,ZZ or 78,ZW, ins(3;1)(q25q27;undetermined) was revealed in chicken by double color fluorescent in situ hybridization (FISH). A fragment of chromosome 1 spanning either from q13-14 to q34-35, or from q14-21 to q36-41 bands, had been translocated to chromosome 3 at a site located between q25 to q27 bands. This has resulted in the generation of an interstitial deletion in chromosome 1 and an insertional translocation in chromosome 3. Chickens with this balanced insertional translocation are asymptomatic carriers and their fertility is not affected, but embryo mortality increases. Greater than 50% occurrence of unbalanced gametes are observed. However, progeny sex ratio is not affected.

Random amplified polymorphic DNA markers in crosses between inbred lines of Rhode Island red and White Leghorn chickens.

Reciprocal crosses and backcrosses were conducted between inbred Rhode Island Red and White Leghorn chickens differentiated for egg production and egg quality traits. Random amplified polymorphic DNA (RAPD) markers distinguishing inbred lines were detected. Twenty-two polymorphic bands were found from screening 120 single 10-mer random primers of which two were consistent with sex-linked markers. Of 90 pairwise two-point linkage analyses completed for the autosomal markers, four close linkages (8.2 cM to 14.9 cM) were significantly different from zero.

Close linkage relationship of the Z-linked pop-eye and silver plumage color loci in the chicken.

The Z-linked pop-eye and the silver plumage color loci in the chicken were tested for linkage using a back cross. The F1 males used were silver, with normal eyes and gold down, pop-eye in coupling (*S *N/*G *POP). The females were gold, pop-eye (*G *POP/W). In previous studies, it had been suggested that both loci were on the short arm of the Z chromosome. There were 13 recombinants among 187 individuals obtained from this mating, indicating that these loci are linked by about 7 cM.

A rapid, polymerase chain reaction-based procedure for identifying mutant restricted ovulator chickens.

Females of the restricted ovulator (RO) strain of White Leghorn chickens fail to lay eggs upon photostimulation and exhibit endogenous hyperlipidemia and atherosclerotic lesions. A mutation in the gene specifying the oocyte vitellogenesis receptor (OVR), a 95-kDa membrane protein that normally mediates the massive uptake of yolk precursors from the serum, is responsible for this abnormal phenotype. Because a single nucleotide substitution (G-->C) is responsible for the defective OVR, a PCR-based procedure, described herein, was developed in order to provide a rapid and accurate method for identifying chickens possessing the mutant allele. Polymerase chain reaction-amplified fragments of apparently identical size (approximately 400 bp) were obtained from genomic DNA using primer pairs specific for either the wild-type or mutant genes. Through cloning and sequencing of the PCR-amplified products, the fragment sizes were determined to be 413 bp each, which included an intron sequence. Polymerase chain reaction-amplified genomic DNA from wild-type (ovr+/ovr+) males, heterozygous carrier (ovr+/ovr-) males, and wild-type (-/ovr+) females all yielded a 413 bp fragment when a primer pair specific for the wild-type gene was used. Because female chickens are heterogametic (ZW), no PCR product was observed in the case of the mutant (-/ovr-) females. When the primer pair specific for the mutant gene was employed, PCR-amplification of genomic DNA from both heterozygous carrier (ovr+/ ovr-) males and mutant (-/ovr-) females, but not wild-type (ovr+/ovr+) males or (-/ovr+) females, also yielded a 413-bp fragment. Employment of the present rapid and accurate procedure would be expected to obviate the need for conventional progeny testing while reducing the time required to identify RO carrier males and mutant females from approximately 1 yr to several days.

Chicken genome mapping: a new era in avian genetics.

More than 460 loci representing either expressed or anonymous sequences have been mapped on to the first comprehensive molecular genetic linkage map of the chicken genome. Here, we review the current status of poultry genome mapping and discuss some of the new opportunities this provides.

A question on the locations of the tardy feathering and henny feathering loci in the chicken.

The locus for tardy feathering (t), previously mapped to the long (q) arm of chromosome 1 of the chicken, was tested for genetic linkage with both the NM 7659 t(Z;1) rearrangement break point (RB) and the henny feathering (Hf) locus. The RB is proximal to the centromere on 1q, and Hf has been reported to be on the proximal one-third of the same arm. Independent segregation of all three markers was found in two separate backcrosses.

Lack of recombination between the Z-linked silver feather pattern locus and the break point of a chromosome translocation: a second occurrence.

A mating was conducted to test the linkage relationship between the Z-linked silver locus (S) and the NM 7659 t(Z;1) chromosome translocation. No recombinants between the break point and S were recovered (n = 187). A previous study had shown no recombination between the S locus and the MN t(Z;3) chromosome translocation. The proximity of these two break points and the endogenous retrovirus ev21 may indicate an unstable DNA segment in this region.

Inheritance of tinted eggshell colors in white-shell stocks.

The present study was conducted to study the genetics of tinted eggshell colors in two breeds of chickens laying white-shell eggs. Reciprocal crosses were made between an inbred White Leghorn line (ES) and an inbred Ancona line (ANC). The F1 birds were intercrossed and F1 females were backcrossed to each of the original lines. Eggshell color from each resultant group was measured using a Minolta chromometer, and a value (e) representing the color intensity adjusted by hue and saturation was used as the measurement criterion. Age, hatch group, and crosses each contributed significantly to the variation seen in eggshell color. Distribution comparisons indicated that two major autosomal loci affected the trait in these lines: one gene having incomplete dominance controls the amount of pigment deposition; the second completely inhibits pigment deposition when homozygous recessive. A test of goodness of fit supported this hypothesis. Genetic components were estimated by linear models. Epistasis, dominance, and additive effects contributed significantly to this trait. No sex-linked effects were noted.

Albinism in White Leghorn chickens.

The appearance in 1988 of an oculocutaneous albino chick in a Single Comb White Leghorn line suggested a new mutational event. This line was closed in 1949, and has been reproduced each spring since then. Subsequent matings indicated that the mutation occurred at the C pigment locus. A mating of the Wisconsin albino (WIA) to cre/cre (red-eyed white) birds showed the mutation to be incompletely recessive to cre. No segregation was apparent when mated to ca/ca (recessive albinism) birds. These data indicate that the WIA mutation is identical to, or very similar to, the previously described tyrosinase-negative ca mutation at the C locus.

Effect of the MN t(1;4) translocation on some economic traits of the chicken.

The F2 progeny from an original mating between chickens that were carriers of the MN t(1;4) chromosome translocation and the inbred WI-ES line were compared to determine if the translocation had any effect on selected economic traits. Homozygous translocation (TT), heterozygous translocation (TN), and karyotypically normal (NN) individuals were compared. Traits analyzed were body weight at 8, 18, 39, and 55 wk of age; shell deformation; Haugh units; egg weights at 32 and 55 wk of age; sexual maturity; egg production; and male fecundity. The TT group had greater body weights at 39 and 55 wk than the TN and NN groups, and at 55 wk the TN group was heavier than NN group. Shell deformation was greater for TT birds at 32 wk. At 32 wk, Haugh units of the TT and TN birds, and the TN and NN birds were not significantly different. The TT eggs were heavier than the TN eggs at 32 wk, which in turn were heavier than the NN eggs. Sexual maturity was reached in the order NN, TN, then TT. Eggs from TT males had the lowest fertility and highest percentage of late dead embryos. There were increased early deaths among embryos from heterozygous males. An unexplained higher number of pips among embryos from normal males was noted. No differences were noted among any other traits in either sex. Results suggest that this translocation may have some effect on production traits.

Estimating meiotic disjunction frequencies in chicken translocation heterozygotes based on embryonic mortality.

Chickens heterozygous for a chromosomal translocation [MN t(1;4)] were intercrossed and the progeny were analyzed for their chromosome complement. A ratio of 1 homozygous translocation carrier to 4 heterozygous translocation carriers to 1 homozygous standard chromosome carrier was noted (n = 520), rather than the 1:2:1 ratio expected from Mendelian segregation. The excess of heterozygous carriers was apparently caused by union of complementary duplication/deficient gametes. Embryonic death occurred in 68% of fertile zygotes. This finding fits very closely to expectations if alternate and adjacent meiotic disjunctions occurred at equal frequencies. As alternate disjunction frequencies increase from 0.5 to 1.0 in inter se matings, the proportion of inviable zygotes among fertilized ova will decrease from 0.625 to 0 and the proportion of translocation heterozygotes among viable progeny will decrease from 0.667 to 0.5. In instances where alternate and adjacent disjunction occur at equal frequency, preferential recovery of translocation carriers will occur. This may contribute to chromosomal diversity within a species, and possibly lead to speciation.

Erythrocyte alloantigen loci Ea-D and Ea-I map to chromosome 1 in the chicken.

A test cross was conducted to analyse some linkage relationships in the chicken. Pea comb (P), naked neck (Na), tardy feathering (t), four erythrocyte alloantigen loci (Ea-C, -D, -I, -P), and the rearrangement break point (RB) of the NM 7092 t(Z;1) chromosome translocation were tested. Significant linkages were found between P and Ea-I (32.9 +/- 4.2), the RB and Ea-D (30.7 +/- 4.3), and t and Ea-D (38 +/- 4.8). The data suggest the linear order of t, Ea-D, and the RB, with t closest to the centromere. Significant linkage was also found between Na and Ea-P (32.4 +/- 4.9), confirming earlier reports.

Spontaneous high density lipoprotein deficiency syndrome associated with a Z-linked mutation in chickens.

A mutant strain of chicken previously identified by a "recessive white skin" phenotype was found to have a profound deficiency in high density lipoprotein (HDL) and apolipoprotein A-I (apoA-I). ApoA-I levels in the mutant chickens were reduced by greater than 90%. Since HDL is the predominant cholesterol transporter in chickens, the HDL deficiency was associated with a greater than 80% decrease in total plasma cholesterol. The mutation segregates with markers linked to the Z-chromosome. The structure of the apoA-I produced by the mutant chickens appeared normal as judged by two-dimensional gel electrophoresis. The genetic and biochemical evidence, therefore, suggests that the mutation is not in the apoA-I structural gene. Turnover studies were performed on labeled HDL or on labeled apoA-I preincubated with HDL prior to intravenous injection. Both types of experiments showed that both defective apoA-I production and hypercatabolism contributed to the HDL deficiency, although defective production made a much larger contribution.

Function of bilateral oviducts in double oviduct hens following surgery.

A double oviduct line of Rhode Island Red chickens has been maintained as a closed flock at the Wisconsin Experiment Station since 1970. Sixty-four percent of the stock reared during the 3-yr study period had complete left and right oviducts. Experiments were designed to determine whether the right oviduct of double oviduct hens was functional. Two surgical procedures were chosen in which either a piece of the left ovary was transplanted to the right side, or the abdominal-midline tunica serosa was opened and the left ovary was pulled to the right side. In one experiment the left oviduct was also made nonfunctional. Laparotomized hens served as controls. Insemination with semen from dominant barred males as a genetic marker, followed by physical examination, confirmed right oviduct function. Hens that formed the egg in the normal left oviduct laid significantly more eggs of much greater weight and had higher percentage fertility than hens with functional right oviducts.

Linear relationship of the loci for barring, dermal melanin inhibitor, and recessive white skin on the chicken Z chromosome.

The Z-linked loci barring (B), dermal melanin inhibitor (Id), and recessive white skin (y), and the MN t(Z;1) Z-linked chromosome translocation breakpoint (TB) were tested for linkage relationships. The linear order was found to be B-Id-TB-y, with B distal from the centromere on the long arm of the chromosome, and y mapping closest to the centromere. Calculated map unit values between markers varied depending on the presence or absence of the chromosome translocation. When tested on a normal chromosome, map distance +/- SE between B and Id was 13.7 +/- 2.2, and the Id-y distance was 39.9 +/- 3.0. The B and y loci showed independent segregation. When B and y were tested in the presence of the translocation, the calculated distance between these markers was 29.8 +/- 4.0. The B locus mapped 19.1 +/- 3.5 from TB, and y mapped 16.8 +/- 3.1 from TB.

Pairing of ZW gonosomes and the localized recombination nodule in two Z-autosome translocations in Gallus domesticus.

Electron microscopic observations of synaptonemal complexes of oocytes from chickens heterozygous for two Z-autosome translocations have been used to identify and study the pairing region of the Z and W chromosomes. The two translocations, MN t(Z;1) and t(OH 10), have breakpoints in opposite arms of the Z, and the arm having the breakpoint of MN t(Z;1) is marked by the terminal C+ band. In both translocations the short arm of the W was specifically paired with the euchromatic short arm of the Z. In MN t(Z;1) only open quadrivalents (74%) and trivalents plus W univalents (26%) were observed, whereas t(OH 10) exhibited, in addition to the prevalent quadrivalents (62%), III + I (19%) and II + II (19%) configurations. The extent of W pairing was slightly decreased in MN t(Z;1) (68.4% of the W chromosomes paired) and considerably decreased in t(OH 10) (25.3% of the W chromosomes paired). Nonhomologous synapsis occurred regularly at the quadrivalent crosspoint in MN t(Z;1) and also in bivalents from t(OH 10). The recombination nodule normally located in the terminus of the pairing region in normal ZW pairs is present in both translocations without any alteration of its frequency or its strict terminal position. Based on these data and previous observations (Rahn and Solari, 1986), it is proposed that an obligatory recombination event occurs at a locus between 0.7 microns and 0.15 microns of the paired ZW telomeres, establishing a recombinational region and a pseudoautosomal region which determine partial sex-linkage and no sex-linkage, respectively. Most of the pairing region of the ZW pair is nonhomologously paired.