With the arrival of new molecular technologies, specifically molecular genetic markers, it is theoretically possible to greatly increase the information available for breeding programmes. Genetic markers are differences in the DNA of animals that can be identified easily in individuals by biochemical simple tests. Such genetic markers provide particularly valuable information when they are located close to or in a gene of interest and some dependence or “disequilibrium” exists between different forms of the marker and different forms of the gene.
Indeed in a population, when the marker and gene are very close the physical characteristics of the animals will be statistically associated with the marker and will stay linked for generations of breeding. If this statistical relationship is detected, individuals can be selected when the desired form of the molecular marker is present, since its presence would be an indication of the desired trait under study. This is known as “Marker Assisted Selection”. By using molecular markers it is then possible to use a simple DNA test (e.g. blood sample) to “genotype” animals and classify those carrying a desire trait before the selection process. Thus, the selection of superior animals can be achieved in a simpler and faster manner than through the standard approach of recording data and analyzing it statistically. Much research in Animal Genetics is currently focused on the search of genetic markers for economically important traits, with the aim of providing new tools for breeding programmes. Research strategies have been aided by the use of easy and reproducible technologies that can be later transferred to member states.
Most genetic studies need a strategic technique that can provide results in a fast, accurate, economical manner, while allowing for high throughput. The TaqMan SNP genotyping Assays provide a highly flexible technology for detection of Single Nucleotide Polymorphisms (SNP). With the simplest workflow available, TaqMan assays are the quickest way to generate genotypic data. It should be added that straight forward screening from a population can be done by pooled DNA for allele frequency studies, making the study less costly and less laborious. Compared to conventional radioactive labelling, this new chemistry offers greater sensitivity, specificity, and is easy to perform because requires no post-PCR processing. More important, the technology simplicity and reproducibility can be easily transferred to member states to continue with the research in their own laboratories.
On a global scale, ruminant diseases caused by gastrointestinal nematode parasite infestations are among the diseases with the greatest impact upon animal health and productivity. It has been known for years that the natural genetic ability of some animals to cope with internal parasites existed. For example, several breeds of are sheep known to have some degree of enhanced resistance and show superior growth compared to other breeds in environments where animals are exposed to helminths. These are typically breeds native to areas where helminth infection occurs, and give the local sheep an advantage over exotic breeds. In theory, obtaining sheep more “tolerant” to helminths can be achieved, via identification of molecular markers for traits known to be involved on conferring resistance to parasites.
The Animal Genetics group at Seibersdorf is trying to develop tools to make this possible. Using available information on the Genbank and data from other previous and on-going research, the INFG (Interferon gamma) and MHC-DRB1 genes have been selected for the identification of putative SNP sites related to parasite resistance. The Animal Production Unit has started the search of possible SNP sites in both genes, with the main objective of obtaining markers to be used as tool in breeding strategies to obtain populations of small ruminants that are more tolerant to helminth infection. In addition, members of the Animal Production Unit and Section are collaborating with researchers from the United States Department of Agriculture, the International Livestock Research Institute and the University of San Paulo on a genome scan of a cross between Dorper and Red Massai sheep to develop genetic markers for helminth resistance.
Studies of the genetics of sheep have shown that it is possible to identify whether sheep are resistant or susceptible to scrapie, an incurable degenerative disease affecting the central nervous system of small ruminants. A single polymorphism (in the so-called PrP locus) has been shown to confer resistance to infection in sheep. However this is not the same scenario in the case of goat, where more information is still needed to better understand the disease mechanisms. To address these problems, the Animal Production Unit is currently developing a test for identification of scrapie resistance and susceptibility based on the use of TaqMan technology. The study is aiming at finding an approximate indication of the PrP allele frequency of individual breeds and eventually identifying susceptible or resistant flocks. This work is expected to yield a tool that can improve our ability to predict disease resistant/susceptibility status and also be used in studies on the biological mechanisms of scrapie.
It is widely known that the autosomal Booroola fecundity gene (FecB) mutation in sheep increases ovulation rate and litter size. In other words, Booroola could offer a possibility for selecting sheep with high levels of prolificacy. By the use of genetic molecular markers, a single mutation causing prolificacy in sheep can be easily detected. The Booroola trait offers a new option that can allow certain breeds producing single lambs to obtain a high level of prolificacy, by genetic introgresion of the desired allele of the FecB. By using a simple detection system (TaqMan technology), it is possible to identify certain breeds with the Boorola mutation, and on that way breeders will be able to select Booroola rams from those breeds to incorporate into their crossbreeding programme.