Efficiency of marker assisted selection

The use of DNA polymorphisms in genetic mapping

The introduction of molecular markers has revolutionized genetics. The range of polymorphisms that are available is increasing and the advent of large-scale cDNA and genomic sequencing is a source of an ever-increasing set of available markers. The ease with which any particular marker type can be applied to an experimental system depends, to some extent, on the amount of genomic information available for that system. However, comparative genomics is enabling a wider range of marker technology to be applied to relatively information-poor systems. The types of markers that are available include restriction fragment length polymorphisms, amplified fragment length polymorphisms, ransom amplified polymorphic DNAs, simple sequence repeats, single nucleotide polymorphisms and small insertions/deletions. The types of questions that can be addressed with these molecular markers include the generation of genetic and physical maps for the identification of interesting loci, the development of marker-based gene tags, map-based cloning of agronomically important genes, synteny mapping, marker-assisted selection and quantitative trait analysis. The continued development of technology including new high throughput methods, for example those being applied to single nucleotide polymorphisms, will change the ease with which current questions can be answered as well as enable new analyses that are presently impossible to undertake.

Supply of genetic information--amount, format, and frequency

The volume and complexity of genetic information is increasing because of new traits and better models. New traits may include reproduction, health, and carcass. More comprehensive models include the test day model in dairy cattle or a growth model in beef cattle. More complex models, which may include nonadditive effects such as inbreeding and dominance, also provide additional information. The amount of information per animal may increase drastically if DNA marker typing becomes routine and quantitative trait loci information is utilized. In many industries, evaluations are run more frequently. They result in faster genetic progress and improved management and marketing opportunities but also in extra costs and information overload. Adopting new technology and making some organizational changes can help realize all the added benefits of the improvements to the genetic evaluation systems at an acceptable cost. Continuous genetic evaluation, in which new records are accepted and breeding values are updated continuously, will relieve time pressures. An online mating system with access to both genetic and marketing information can result in mating recommendations customized for each user. Such a system could utilize inbreeding and dominance information that cannot efficiently be accommodated in the current sire summaries or off-line mating programs. The new systems will require a new organizational approach in which the task of scientists and technicians will not be simply running the evaluations but also providing the research, design, supervision, and maintenance required in the entire system of evaluation, decision making, and distribution.