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Centre for Genetic
Improvement of Livestock Gene Tracking |
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New genetic
technologies that more efficiently trace the inheritance of key genes for
production traits may lead to an improved selection program for dairy
breeders.
Prof. Gerald Jansen, Centre for Genetic Improvement of Livestock, in collaboration with visiting scientist Dr. Giulio Pagnacco from Italy's University of Milan, has adopted a method, called molecular marker technology, to track important genes. If it works in industry, Jansen says it has the potential to change the way breeders select their parent stock. The team's method involves the identification of genes called quantitative trait loci (QTL) -- segments of DNA that, if inherited by the calf, will lead to a small improvement in a certain trait, such as milk protein levels or rate of growth. The final productivity of a grown calf for any one quality depends on how many positive QTLs it inherits for that particular trait. "By using this new technology, we can figure out the specific genes that offspring have inherited from their parents," says Jansen. "This could, for example, significantly improve our accuracy in selecting test bulls." On average, each calf has a 50 per cent chance of inheriting a particular QTL varient from one of its parents. The industry bases its relatedness estimates on this average, assuming a calf will be born with exactly half of its genetics from the dam and half from the sire. But, as Jansen points out, the 50 per cent estimate is inexact. Since the combination of genes passed to a calf is random, it can receive more favourable QTL varients from one parent than the other. The result? For a trait of interest, certain calves can be genetically more similar to the sire than the dam or to one sibling over another. |
By using genetic markers -- or gene landmarks
-- known on either side of a specific QTL, Jansen and Pagnacco can compare
the DNA of full siblings to find which may have the upper hand for
production potential. In some cases, they may find that a calf is missing
genes from the sire and immediately exclude it from testing...a method
much faster and more economical than discovering genetic shortcomings
after years of breeding.
Jansen subjected this technique to a computer simulation, going head-to-head against today's conventional genetic testing programs. Tracking the progress of computerized herds of 200 animals for five generations, Jansen and Pagnacco found the new technique increased the rate of trait-specific genetic improvement by up to eight per cent over two generations -- before settling to a final overall improvement of two per cent above standard methods. Jansen sees the results as a first small step in the move toward better genetic improvement strategies. "We're looking to go far beyond this simulation," says Jansen. "By expanding the process to include multiple QTLs and using it alongside other genetic techniques, we could significantly enhance the accuracy and efficiency of dairy breeding programs." This research is supported by DairyGen (formerly the Cattle Breeders' Research Council). |
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