A quick and simple method has been developed to detect the presence or absence of the endogenous Rous-associated virus (RAV) element ev1 in chickens. The procedure consists of a one-tube multiplex polymerase chain reaction (PCR) involving three oligonucleotide primers that are specific for the upstream flanking region, the long terminal repeat (LTR), and the downstream flanking region of the proviral insert, respectively. The multiplex reaction allows for the unambiguous discrimination between ev1+/ev1+ homozygote, ev1-/ev1- homozygote, and ev1+/ev1- heterozygote birds. The method works best with purified genomic DNA as substrate, but can also be used with rapidly prepared, "crude" DNA samples. The combination of speed with the safety of a nonradioactive procedure, and the ability to perform large numbers of assays by a semi-automated procedure, make this method attractive for large-scale screening projects. The ev1 locus has been used as a model system to demonstrate the feasibility of the PCR diagnostic approach. However the same principle should be applicable to the analysis of other RAV-type ev loci, as well as endogenous elements belonging to other families of viruses as sequence information for the flanking regions of these inserts becomes available.
ABSTRACT 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 × 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.
The molecular architecture of the sex-linked late-feathering region of the chicken genome is still poorly defined. Current evidence points to a strong association between the presence of the endogenous viral element ev 21 and the late-feathering phenotype. However, analysis at the molecular level has demonstrated that this is not a simple case of insertional mutagenesis. Instead, the structure of the region of the chicken genome containing the feathering locus is complex and variable between and within lines of chickens. Significant clues to the molecular structure of this genomic region can be obtained by analyzing rare and revertant genotypes. However, searching for rare genotypes can only be carried out effectively using quick screen methodology. This paper describes a quick, polymerase chain reaction-based test for ev 21 that facilitates the search for rare genotypes.
Se midieron algunos rasgos seminales y morfologicos en gallos de dos lineas control (!lineas 5 y 7), dos lineas seleccionadas por porcentaje de postura, del primer huevo puesto hasta los 273 dias de edad (lineas 1 y 9) y dos lineas seleccionadas (lineas 3
Avian diseases in the broad sense include health problems arising from adverse physical environment or inadequate nutrition, developmental disorders, and infectious and parasitic diseases. Genetic improvement is of particular importance in the reduction of losses from the latter two groups of diseases. There is considerable knowledge of genetic mechanisms underlying many developmental disorders, mainly where major genes are involved, but their molecular basis is largely unknown. Ample evidence exists that genetic factors play an important role in resistance to infectious diseases. Such resistance appears to be controlled by polygenes, and major genes underlying the resistance have been identified in only a few instances. Knowledge of molecular bases of resistance mechanisms, such as the major histocompatibility system, immune response, and pathogen receptors, is rapidly increasing. Also, the molecular structure of many pathogen genomes is known and can be used in devising approaches to the improvement of host resistance. Molecular genetic information may provide tools for genetic improvement of resistance by selection using markers that are either linked to or are themselves components of resistance genes. Such selection does not require exposure to pathogens and, therefore, is desirable from the animal-welfare point of view. As well, DNA fingerprinting can improve the efficiency of transfer of genetic resistance by crossbreeding and backcrossing. For industrial applications, molecular gene transfer is justified primarily to introduce new resistance mechanisms, exemplified by pathogen-mediated resistance or antisense RNA, that do not exist in the avian species. Improvements of existing resistance mechanisms by gene transfer should await perfection of methods such as the culture of avian embryonic stem cells and homologous recombination. Progress in molecular mapping of avian genomes and further elucidation of molecular bases of resistance will play an important role in future improvements of genetic resistance to diseases in poultry.
Several new, powerful techniques for the manipulation of living cells and their components are globally referred to as biotechnology. They have the potential to bring about dramatic improvements in livestock production. The Symposium papers that follow review the relevant advances and consider the role of biotechnology in future animal production research. Key words: Biotechnology, animal science, genetic engineering, rumen microflora, embryo manipulation
Summary Animal production efficiency, and product volume and quality can be greatly increased by reducing disease losses. Genetic variation, a prerequisite for successful selection, has been found in animals and poultry exposed to a variety of viral, bacterial and parasitic infections. Breeding for disease resistance can play a significant role alone or in combination with other control measures including disease eradication, vaccination and medication. Feasibility of simultaneously improving resistance to specific diseases and production traits has been demonstrated. However, selection for specific resistance to all diseases of animals and poultry is impossible. Development of general disease resistance through indirect selection primarily on immune response traits may be the best long‐term strategy but its applicability is presently limited by insufficient understanding of resistance mechanisms. Another hindrance may be negative genetic correlations among various immune response functions: phagocytosis, cell mediated and humoral immunity. To better assess the feasibility of increasing general disease resistance by indirect selection we must obtain estimates of heritability for immune response, disease resistance, and economic production traits, as well as genetic correlations among these traits. The present level of disease resistance in farm animals resulted from natural selection and from correlated responses to selection for production traits while the influence of artificial selection for resistance was minimal. Future research should be directed towards developing and applying breeding techniques that will increase resistance to diseases without compromising production efficiency and product quailty. This will require cooperation of immunogeneticists, veterinarians and animal and poultry breeders. Significant progress in the improvement of resistance to diseases may result from the application of new techniques of molecular genetics and cell manipulation.
