Variance component models for X-linked QTLs.

This paper discusses the theory and implementation of a model for mapping X-linked quantitative trait loci (QTL). As a result of X inactivation, a female's body is subdivided into a number of patches. In each patch one of her two X chromosomes is randomly switched off. This smooths the allelic contributions in a heterozygote and implies that females should show less trait variation than males for an X-linked trait. The latest version of the genetic analysis program Mendel incorporates a simple variance component version of this model. An application to head circumference in autistic children illustrates Mendel in action.