Chapter 5: Genetic models

Even though for some animal species the full genome has been mapped, we still cannot ‘see’ which in a population of animals would be the genetically superior ones. We cannot read the working of the DNA in full detail yet. So instead we need to make an estimate of the genetic potential of the animal based on its phenotype. How we can do that will be the subject of the chapter about ranking the animals. In this chapter we will look into how we can get an impression of how much of the phenotypic variation in performance we observe in our population is due to actual genetic differences between the animals. For example, is a cow that produces an average of 25 kg per day in her lactation indeed a genetically better cow than a cow that produces 15 kg per day? Is a horse that always has high scores in a dressage test indeed a genetically better horse than the one that scores much lower? And why is the full sister of that excellent hunting dog not also performing at top level with that same trainer? The answers to these question may not all be the same. In this chapter we will find out why.

If we look at the diagram again with the stages involved in the breeding program circle, then we are at the stage number 4. In the previous chapters we have identified the breeding goal and we have collected measurements on phenotypes and genotypes and pedigree of the animals. In this chapter we will define the genetic model that we will use as tool to translate the measurements into a set of criteria that we can use to rank animals for selection.

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