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 is 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 Polymorphisms (SNPs). The genomic Genomic selection is based on the analysis of 10.000 10000 up to 800.000 800000 SNPs. This high number of genetic markers is used as input in a genomic prediction formula that predicts the breeding value of an animal.
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A complicating factor is recombination between SNPs and QTLs. This means that the value of animals in the reference population slows breaks 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 while data from the oldest generations can be deleted, but the reference population should always have a sufficient (large) size.
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