The fourth application of genetic markers is genomic selection. Genomic selection is a form of marker-assisted selection in which a very large number of genetic markers covering the whole genome are used. In this case all quantitative trait loci (QTL) are closely linked at the chromosomes with at least one marker. The large number of markers is obtained by chips using Single Nucleotide Polymorphims (SNPs). The genomic selection is based on the analysis of 10.000 up to 800.000 SNPs. This high number of genetic markers is used as input in a genomic prediction formula that predicts the breeding value of an animal.
Definitions
Genomic selection is selection for a trait of interest with a very large number of genetic markers covering most QTL-loci related to the trait.
An SNP is a single nucleotide polymorphism caused by a mutation of a single nucleotide.
A complicating factor is recombination between SNP’s and QTL’s. This means that the value of animals in the reference population slows down when the number of generations between them and the test population increases (more chance for recombination events).
And it implies that it is highly recommended to continue the recording of phenotypic data of future generations. The best policy is to extend the reference population with DNA- and phenotypic data from new generations and to delete the oldest generations, but the reference population should always have a sufficient (large) size.