DNA fingerprinting, a technique based on the detection of hypervariable minisatellite regions in DNA restriction fragments, was tested for its applicability to conduct population genetics in poultry. Using MspI digestion and phage M13 DNA as a probe, between 25 and 35 minisatellite-containing DNA fragments were observed per bird. Comparison of the banding pattern of offspring with their parents revealed that the bands were inherited as stable genetic traits. The variability of the DNA fingerprinting pattern was reduced in inbred strains. DNA fingerprints of chickens from five well-defined populations of known genetic relationships were analyzed and indices of genetic distances were computed. They correctly reflected the history of these strains, indicating that DNA fingerprinting may be a powerful tool to characterize genetic relationships between different breeding populations of the same species.

If the poultry industry hopes to continue to flourish, the identification of potential quantitative trait loci (QTL) for production-related traits must be pursued This remains true despite the sequencing of the chicken genome. In view of this need, a scan of the chicken genome using 72 microsatellite markers was carried out on a meat-type x egg-type resource population measured for production and egg quality traits. Using a Bayesian analysis, potential QTL for a number of traits were identified on several chromosomes. Evidence of eight QTL regions associated with a total of eight traits (specific gravity, albumin height, Haugh score, shell shape, total number of eggs, final body weight, gain, and feed efficiency) was found. Two of these regions, one spanning the area of 263/287 cM on GAA01 and the other spanning the area of 23/28 cM on GAA02, were associated with multiple QTL.

Alleles of the growth hormone (GH) gene and GH receptor (GHR) gene were analyzed for association with juvenile body weight (HBWT), age at first egg (AFE), the hen-day rate of egg production (HDR), egg specific gravity (SPG), and egg weight (EWT) in a strain of White Leghorns. The particular strain segregated at near equal frequencies for two GH alleles defined by differences at three restriction fragment length polymorphisms (RFLP) and for two GHR alleles defined by a single RFLP. The GH genotype was significantly associated with AFE (P < or = 0.04) as well as HDR from 274 to 385 d (P < or = 0.04) and 386 to 497 d (P < or = 0.0003). The GHR genotype (haploid in female chickens) had trends for association with HBW (P < or = 0.06) and HDR from AFE to 273 d (P < or = 0.07). The effects on the egg quality traits SPG and EWT were not significant. Regression analysis revealed that HDR was associated negatively with AFE and positively with HBWT. The slope of the regression line of HDR on AFE varied with the GH genotype, with the effect that the differences in HDR between GH genotypes was relatively small in chickens with early AFE and large in chickens with late AFE. Similarly, the slope of the regression of HDR on HBWT varied between GHR genotypes, with the result that the effect of the GHR genotype on HDR in chickens with low HBWT was opposite to its effect in chickens with high HBWT. The complex relationship between genotypes and traits may reflect gene interaction and indicates that simple models based on additive gene effects may not be adequate for the dissection of the genetic architecture of quantitative traits.

Lymphoid leukosis (LL) is virus-induced, lymphoblastic malignancy of chickens that can be congenitally transmitted. Mortality from LL is generally low. Effects of LL virus (LLV) on production and mortality were investigated in approximately 2000 Leghorn pullets in each of two consecutive years. The pullets were from nine strains developed in Ottawa, of which three were unselected control strains and six were strains under selection for up to 27 generations for high egg production and a complex of related commercially important traits. The overall frequency of birds shedding LL virus of gs antigen into eggs (LL-S) was significantly lower in the selected strains (3.9%) than in the control strains (18.5%), indicating that LLV may have negative effects on production and cause elimination of LL-S birds by selection. Such significant effects were indeed detected: the LL-S pullets produced to 497 days of age in 1976 and 1977, respectively, 30 and 25 eggs less per hen-housed than the nonshedders. The LL-S birds matured sexually later, produced smaller eggs at a lower rate, and their eggs had a lower specific gravity, indicating thinner shells. Mortality from all causes to 497 days was significantly higher in LL-S birds (+14.8%) in 1976. In 1977 the increase (+5.5%) did not reach statistical significance. In both years the mortality from LL itself remained very low. In another study, eggs from one of the control strains were incubated and hatched from the dams were 291 and 483 days old. The eggs from LL-S dams had 2.4% lower fertility and 12.4% lower hatchability. The effects on hatchability were more pronounced in the older dams. Since the lower production of LL-S birds results in a lower frequency of such birds in strains selected for high egg production, it is suggested that a part of the difference between the performance of the selected and control strains (delta S) is due to reduction in the frequency of LL-S birds (delta L) rather than due to true genetic gain. In this study, the size of delta L relative to delta S was estimated at 4 to 14% for egg production and 3 to 7% for egg weight. The negative effects of LLV infection on egg production, mortality, hatchability, and genetic gains show the desirability of producing chickens free of LLV infection.

Endogenous viral (ev) genes are DNA sequences residing permanently in the genome of most chickens that have a high degree of homology to avian leukosis viruses (ALV). Association of ev genes with production trait differences was studied in White Leghorns free of exogenous ALV. The Cornell Strain K and S chickens used in Experiment 1 had multiple ev genes. In each of four lines of chickens in Experiment 2, there was a 1:1 segregation of full-sibs free of ev genes and those carrying one ev gene: ev-12 that produces the complete endogenous virus, ev-3 or ev-6 that express certain viral antigens, or ev-1, a silent gene. In Experiment 1, the presence of genes ev-10 or ev-19, known to produce the complete virus, was associated with a 9% reduction in the annual egg production rate (P less than .05) in Strain S. Similarly, the presence of the virus-producing ev-12 in Experiment 2 was associated with an 8% reduction of annual egg production rate (P less than .05), a 2.2-g reduction in egg weight (P less than .01), and a .003 reduction in egg specific gravity (P less than .01). No significant effects of ev genes on age at first egg, Haugh unit score, percentage of eggs with blood spots, and body weight of hens were observed. It was concluded that ev genes producing complete endogenous virus are associated with production trait differences similar to those associated with subclinical infections with exogenous ALV.