Levels of linkage disequilibrium in a wild bird population

Abstract

Population-based mapping approaches are attractive for tracing the genetic background to phenotypic traits in wild species, given that it is often difficult to gather extensive and well-defined pedigrees needed for quantitative trait locus analysis. However, the feasibility of association or hitch-hiking mapping is dependent on the degree of linkage disequilibrium (LD) in the population, on which there is yet limited information for wild species. Here we use single nucleotide polymorphism (SNP) markers from 23 genes in a recently established linkage map of the Z chromosome of the collared flycatcher, to study the extent of LD in a natural bird population. In most but not all cases we find SNPs within the same intron (less than 500 bp) to be in perfect LD. However, LD then decays to background level at a distance 1cM or 400-500 kb. Although LD seems more extensive than in other species, if the observed pattern is representative for other regions of the genome and turns out to be a general feature of natural bird populations, dense marker maps might be needed for genome scans aimed at identifying association between marker and trait loci.

Figure 1

Plot of pair wise measures of D′ (open squares) and r² (solid dots) versus genetic distance along the collared flycatcher Z chromosome.

Figure 2

Fraction of D′ values exceeding 0.5 for the interval 0–20 cM.

Figure 3

D′ values for intergenic pairs of SNP markers located within a physical distance of 0–1000 kb in the chicken genome.