DNA Testing: What We Know,
What We Don't Know and How To Use It
SIOUX FALLS, S.D. (Dec. 3, 2012) — It’s a blueprint for life, an instruction manual for everything that functions in a living thing. That’s how geneticist Michael Gonda described DNA to an audience gathered for the Applied Reproductive Strategies in Beef Cattle (ARSBC) symposium Dec. 3-4, in Sioux Falls, S.D. A South Dakota State University (SDSU) assistant professor and researcher, Gonda reviewed the development and application of DNA testing to aid genetic selection of cattle for breeding.
Gonda explained how a single gene can be responsible for the expression of certain simply inherited traits, while multiple genes influence complex traits. A DNA test for the presence of a gene known to be associated with a simply inherited trait may be highly accurate. A test for a gene associated with a complex trait may not be particularly accurate, because the complex trait is controlled by perhaps hundreds of genes. Consequently, not all DNA tests predict genetic merit with equal accuracy.
"To know if a DNA test is any good, we need to know what percentage of genetic variation is explained by the test," stated Gonda. "No DNA test can explain all the genetic variation for a trait, but the percentage needs to be high."
According to Gonda, some DNA tests are breed-specific, while others can be applied to cattle of any breed. Generally, breed-specific tests are more accurate. Ideally, he added, more highly accurate DNA tests applicable to multiple breeds will be developed in the future.
Gonda said the best practical application of DNA tests is to incorporate results in the calculation of expected progeny difference (EPD) values for respective genetic traits. The result, a genomic-enhanced EPD, then includes information representing an animal's pedigree, individual performance information, available progeny performance information and DNA test information. The significant advantage over traditional EPDs is the higher accuracy of genomic-enhanced EPDs as predictors of genetic merit.
"DNA tests can be developed for most traits for which there are EPDs, and genomic-enhanced EPDs are going to be the standard for most breeds because of their higher accuracy," said Gonda.
Comprehensive coverage of the symposium is available online at www.appliedreprostrategies.com. Compiled by the Angus Journal editorial team, the site is made possible through sponsorship by the Beef Reproductive Task Force and LiveAuctions.tv.
Editor's Note: This article was written under contract or by staff of the Angus Journal. To request reprint permission and guidelines, contact Shauna Rose Hermel, editor, at 816-383-5270.