Correcting for classification errors when estimating the number of genes using recombinant inbred chromosome lines

Techniques based on intercultivar chromosome substitution lines in wheat (T riticum aestivum L.) have been used to identify and locate the genes contro lling quantitative traits on a specific chromosome. For a particular trait, the number of segregating loci affecting differences between two parental lines are generally determined by the frequency distribution of recombinant inbred chromosome lines (RICLs). Recombinant inbred chromosome lines are t he inbred progeny of crosses between a chromosome substitution line and its parent cultivar. The determination of the presence and the number of segre gating loci becomes difficult (i) when the distribution exhibits no clear d iscrete classes, (ii) when there is a considerable chance of misclassifying lines into parental and recombinant types, and (iii) when loci are linked. We describe an approach to estimate the number of segregating loci respons ible for the difference between a chromosome substitution line and parental cultivar using the derived RICLs when classification errors are likely. We also discuss the effects of linked loci on the estimates. The method was u sed to estimate the number of genes on chromosome 3A controlling grain yiel d, kernels spike(-1), kernel weight, spikes m(-2), grain volume weight, pla nt height and anthesis date in wheat.