Recombinant inversion chromosomes in phenotypically normal chickens.

Some progeny resulting from interbreeding of individuals heterozygous for a pericentric inversion of chromosome 1 in the chicken have the two complementary types of recombinant chromosomes arising from a single crossing-over within the inverted segment. These individuals are capable of reproduction. Their progeny can have one or the other of the two recombinant chromosomes or, if crossing-over occurs, either a normal or an inversion chromosome.

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.

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.

Additional linkage relationships within the Z chromosome of the chicken.

Genetic linkage tests were conducted using four Z-linked loci and three Z-linked chromosome rearrangements (interchanges). Z-linked recessive white skin (y) segregated independently from the Z-linked barring (B) and silver (S) loci. A map distance of 18.2 +/- 3.2 was found between y and the MN t(Z;1) interchange. A previous report had shown that B was located 22 map units from this interchange, therefore, because B and y were found not to show measurable recombination, the linear order is B-interchange-y. The MN t(Z;3) interchange was tested against S, and no recombinants were recovered in 217 backcross progeny, indicating very close genetic linkage. The NM 7659 t(Z;1) interchange was tested against the dermal melanin locus (id+) and independent assortment was noted. This supports other work that has shown that the S and id+ loci lie on opposite arms of the Z chromosome. Evidence is reviewed that supports the concept that S and the NM 7659 and MN t(Z;3) interchange break points are located on the short arm, while B, id+, y, and the MN t(Z;1) interchange break point are located on the long arm of the Z chromosome.

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.

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.

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.

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.

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.

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.

Live monovular twin chicks from a single yolk chicken egg.

Monovular fully formed twin chicks were recorded from a single-yolked egg. The chicks were attached to a common umbilical cord. One of the twin chicks survived for 10 weeks and the other for 4 days.

Studies of the pirouette mutation. 2. A detrimental phenotypic interaction with naked neck.

During a study to determine if any genetic linkage existed between the chicken mutations pirouette and naked neck, it was found that when both traits are expressed simultaneously in an individual, an "automutilation" condition can be created in some cases. The tremulous head movements of naked neck-pirouette chicks cause scraping of the skin on the neck against the egg shell during hatching, resulting in lacerations of the neck in varying degrees. Because of this potential for injury, it is suggested that matings between carriers of tremulous neurological disorders and carriers of mutations that result in lack of down cover be avoided whenever possible.

Studies of the pirouette mutation. 1. Lack of linkage association with marked regions of chromosomes 1 and 2.

The pirouette mutation was tested for possible genetic linkage with naked neck, tardy feathering, the MN t(Z;1) 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.

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.

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.

A study of linkage relationships of blood group P with naked neck, silkie feathering, and recessive white in chicken.

Linkage relationships of blood group P (Ea-P), naked neck (Na), silkie feathering (h), and recessive white plumage (c) were studied to attempt to clarify the h-Na-Ea-P region of linkage group III of the chicken. The Na-Ea-P linkage values obtained in this test agreed with previous reports, and pooled data were used to recalculate a map distance of 27.9 +/- 2.3 map units between these two loci. A significant chi square for linkage was calculated between Na and c; however, because of the relatively low numbers of progeny tested, the high linkage value calculated, and the absence of detectable linkage between c and the other marker genes, this was probably a chance deviation. All other linkage relationships appeared negative, supporting the current suggested linear order of these loci as h-Na-Ea-P with c not being in this chromosomal region.

Mapping of the genes for pea comb, blue egg, barring, silver, and blood groups A, E, H, and P in the domestic fowl.

Five chromosomal rearrangements involving chromosome 1 were utilized to test linkage relationships of the blue egg--pea comb--naked neck (O-P-Na) linkage group. An F1 stock was created by crossing rearrangement carriers with individuals carrying the traits being studied. The F1 was then backcrossed to recessive, normal chromosome tester stocks. Chromosomal and phenotypic descriptions were made for each of the segregating progeny. Significant linkage relationships were shown for blue egg and pea comb on the proximal one third of the short (p) arm of chromosome 1. No linkage was found for naked neck. Barring and silver were tested against the two arms of the Z (sex) chromosome, and the linkage values suggest that these loci are on opposite arms. Blood group loci linkages between Ea-H and W4, Ea-P and Na, and Ea-A and Ea-E were confirmed. However, no linkage was observed between these loci and the marker rearrangements on the p arm of chromosome 1.

Effect of dietary zearalenone on reproduction of chickens.

Variable quantities of zearalenone (0, 10, 25, 50, 100, 200, 400, or 800 mg/kg diet) were incorporated into a practical laying hen diet and fed to 30-week-old White Leghorn females in egg production. During the 3 week pretest and 8 week experimental periods hens were inseminated weekly with .05 ml of pooled semen from males fed normal diets. Zearalenone was without effect on egg production, egg size, feed consumption, change in body weight, fertility, hatchability of fertile eggs, growth of progeny to 3 weeks of age, comb, weight, oviduct weight, heart weight, liver weight, spleen weight, egg shell thickness, Haugh units, blood hematology, serum calcium, serum inorganic phosphorus, and serum alkaline phosphatase. Zearalenone above 50 mg/kg of diet caused reduced serum cholesterol. In a reciprocal study, adult male New Hampshire chickens were fed diets containing 0, 100, or 800 mg/kg zearalenone for an 8 week period. Semen was collected and inseminated into White Leghorn females fed normal diets. Zearalenone was without effect on fertility or hatch of fertile eggs resulting from matings of these males. Zearalenone resulted in reduced serum inorganic phosphorus, serum cholesterol, and serum alkaline phosphatase in males. Histological examination of a number of tissues in both males and females revealed no changes due to zearalenone feeding. It is concluded that zearalenone up to 800 mg/kg of diet is without effect on reproductive performance of mature chickens.

Relationship of plasma estradiol and progesterone levels to egg productivity in domestic chicken hens.

Female chickens from eight different genetic stocks, ranging from 13 to 21 months of age, and exhibiting various levels of egg production were studied. Plasma samples were collected between 1700 and 2200 hr to determine basal circulating levels of progesterone (P4) and 17 beta-estradiol (E2) by radioimmunoassay. Linear regression analysis was used to describe the relation between mean hormone levels (E2, P4, and E2/P4) and mean egg production from these groups, and correlation coefficients were used to evaluate the general usefulness of these hormone parameters for estimating egg production within a group or flock of hens. Of the three hormone parameters evaluated, basal circulating E2/P4 was found to be the best estimator of egg productivity.