The equation: Phenotype = Genotype + Environment, represents how the level of performance of a trait (Phenotype), is the result of genetic makeup of the animal and all environmental (non-genetic) influences. Genotype can be thought of as the underlying genetic potential of animals to reach a level of performance for a given trait. Genotypes are established at conception, inherited from parents. Selection and mating decisions made by cattle producers impact genotypes. Thereby, wise selection and mating decisions, informed by analyzing the components of your production system, have the potential to create better genotypes.
Genotype has two components, these are:
Breeding Value (BV), whichis based on the additive effect of individual genes. BV is the sum total of these additive effects of individual genes, across an animals entire genome, which influence any specific trait of interest. BV is the best indicator of a bull or heifers genetic value as a parent. Expected Progeny Differences (EPDs) are estimates of an animal’s BV. Selection of breeding stock based on EPDs is a powerful tool to improve the additive genetic merit of cowherds and calf crops. EPDs are available for reproductive traits, growth traits and carcass traits. Since BV is based on the additive effect of individual genes, it is transmittable from generation to generation. Additive genetic change is cumulative and permanent in selected populations of cattle.
Gene Combination Value (GCV), also commonly referred to as the non-additive component of genotype, is the effect of gene pairs at loci across the genome. Mating decisions, involving the choices we make to crossbreed or inbreed, determine GCV. For example, if we make the mating decision to use an Angus bull on our Hereford cows, we are crossbreeding for the sake of creating hybrid vigor (heterosis). The resulting F1 generation of black-baldy calves will have a maximum level of individual heterosis based on GCV, as an Angus gene will be paired with a Hereford gene across all loci. Since GCV is based on the pair of alleles at a given locus, and since genes from a specific locus can’t be transmitted in pairs, GCV can’t be passed from parent to offspring.
Tips for Building Better Genotypes:
- Each selection and mating decision should be intentional, deliberate and made for a purpose. Selection decisions impact BV. Mating decisions impact GCV.
- Choose breeds (and breeding stock within those breeds) with high breeding value for traits of economic importance to your operation.
- Crossbreeding (to increase GCV/hybrid vigor) does not replace additive genetic merit, it builds off of it.
- Purebred animals are an essential component for effective crossbreeding programs.
