QTL
A quantitative trait locus (QTL) is a polymorphic locus which contains alleles that differentially affect the expression of a continuously distributed phenotypic trait. Usually it is a marker described by statistical association to quantitative variation in the particular phenotypic trait that is thought to be controlled by the cumulative action of alleles at multiple loci.
Added in respose to request by Simon Twigger November 14th 2005.
SO:0000771
quantitative trait locus
sequence
biological_region