Mapping quantitative trait loci in complex pedigrees: A two-step variance component approach

There is a growing need for the development of statistical techniques capab le of mapping quantitative unit loci (QTL) in general outbred animal popula tions. Presently used variance component methods, which correctly account f or the complex relationships that may exist between individuals, are challe nged by the difficulties incurred through unknown marker genotypes, inbred individuals, partially or unknown marker phases, and multigenerational data . In this article, a two-step variance component approach that enables prac titioners to routinely map QTL in populations with the aforementioned diffi culties is explored. The performance of the QTL mapping methodology is asse ssed via its application to simulated data. The capacity of the technique t o accurately estimate parameters is examined for a range of scenarios.