The Pattern of Linkage Disequilibrium in Livestock Genome

Linkage disequilibrium (LD) is bases of genomic selection, genomic marker imputation, marker assisted selection (MAS), quantitative trait loci (QTL) mapping, parentage testing and whole genome association studies. The Particular alleles at closed loci have a tendency to be co-inherited. In linked loci this pattern leads to association between alleles in population which is known as LD. Two metric parameter Dˊ and r2 were suggested for measuring the extent of LD in population. D' are more influenced by variation in allele frequencies than r2. Until recently all research on LD was carried out by microsatellite, which reported high level of Dˊ in wide extent. As progressing on large scale genomes sequencing a huge number of single nucleotide polymorphism (SNPs) were detected on genome and microsatellite replaced by SNP in such researches. By using SNP, high level of LD in short distance has been reported. Many factors can affect LD such as selection, migration, genetic drift, mutation, small finite population size and recombination. So, LD is basic tools for exploring the genetic basis of quantitative traits in livestock. Likewise, comparative LD maps make a capable us to examine the degree of diversity between breeds and to discover genomic regions that have been subject to selection. Therefore, this review states concept and current approach to estimating LD and extent of LD in livestock population.