Genomic selection

Abstract

In recent decades, along with the developments of the molecular approaches, many researches were done to detect genes or chromosome segments that affect the economical traits of domestic animals. Despite extensive researches about the marker assisted selection (MAS) method, there has been limited implementation of MAS and minor increases in genetic gain due to its several limitations. The successful completion of the human genome sequence and huge developments in high-throughput assays for genotyping single nucleotide polymorphisms (SNP) across the genome have provided the possibility to apply MAS in genomic scale, which is called genomic selection. Genomic selection predicts the total genetic values using genome-wide dense marker maps so that all QTLs are in linkage disequilibrium with at least one marker. Calculation of genomic breeding values requires estimating SNP effects from a subset of animals in the population with information on both phenotypes and markers genotype called the reference population. Estimated markers effects in the reference population are then used to calculate genomic breeding values of selection candidate individuals in the evaluation population which only have markers information. According to the literature, factors affecting the accuracy of genomic evaluations are the heritability of the trait, the size of the reference population, extent of relationships between selection candidates and the reference population, the method used to estimate marker effects, linkage disequilibrium among markers and QTLs, and the distribution of QTLs effects. To summarize, genomic selection has many advantages over traditional methods including increasing the accuracy of breeding value prediction, shortening the generation interval for many traits and thus improving the rate of genetic gain, and decreasing evaluation costs. Furthermore, genomic selection by using genetic markers better predicts Mendelian sampling term of breeding values and decreases the inbreeding rate compared to traditional selection.