What is a Genotype?
- The genetic makeup of an organism or group of organisms with reference to a single trait, set of traits, or an entire complex of traits.
- The sum total of genes transmitted from parent to offspring.
Why do we need to Genotype?
The conventional way to measure the genetic merit of progeny is to raise a cow, impregnate her, and have her raise progeny. It takes several years to evaluate the progeny and decide whether she’s any good. With genomics, the producer can take a tail hair or other tissue sample when she’s a day old and get exactly the same information.
If I have a young bull and I want to evaluate his genetic merit, traditionally I put him out with a group of heifers, he impregnates them, and they calve. Their progeny grows up, are weaned, and put into a feedlot, where they are evaluated as they’re prepared for market. By the time I get the data on the first progeny, that bull has sired another set of calves and he’s out in the pasture working on his third set. That’s a risk management situation. I want to know before I put him out the first time whether he’s any good. I don’t want to wait until he’s 3 or 4 years old and sired three set of calves, before I realize I’ve made a mistake: Dr Steward Bauck – GM at GeneSeek.
Technological progress is inevitable, as well as extremely advantageous in today’s farming enterprises, but should not replace solid practices like physical measuring and evaluation of animals. Phenotypical information is still necessary to support and verify genotyping.
The Brahman Society introduced genotyping for the first time to members as part of the Beef Genomics Project that was initiated in 2015. Tying in with the BGP, Brahman is trying to promote genotyping of as many animals as possible. Once we have a minimum number, data from Australia and Southern-Africa can be combined to calculate GEBVs for all involved countries. This will further aid the construction of a reference population, which is partly the purpose of the BGP. GEBVs will allow the breeder to do more accurate selection of suitable breeding animals at a younger age.
Advantages and Disadvantages
The use of DNA marker information can allow for early prediction of the genetic merit of an animal before phenotypic records are collected thus increasing the accuracy of young sires and decreasing the generation interval. In some instances, traits are expensive to measure (tenderness, feed intake) or lowly heritable (stay-ability, heifer pregnancy) and thus molecular information can be of greater benefit. As with any new technology, the cost of DNA marker tests is decreasing with time. However, careful economic analysis must be performed prior to implementing any new technology for selection or management purposes to determine if the end results justify the cost.
The Value of Improving Accuracy
The uncertainty surrounding early predictions of genetic merit arise as a result of Mendelian sampling. Every animal is passed a random sample of alleles from each parent, half coming from the dam and half from the sire. We have an estimate of the average effect of what was passed from parent(s) to offspring in the form of pedigree estimates, but the certainty with which we know this estimate is correct (i.e., the accuracy) is low. As more information is collected, such as an individual’s own record and data from progeny, accuracy increases. For lowly heritable traits like measures of reproduction, it can take a considerable number of off-spring to reach high accuracy levels.