QTL mapping.

Most biologically relevant traits are quantitative, controlled by multiple genes, and can be influenced by the environment. The multiple genes, collectively called quantitative trait loci (QTL), segregate according to Mendel's law of inheritance. DNA markers also follow Mendelian expectations but with no apparent effects on quantitative traits. The genomic positions of DNA markers are known or can be inferred with computational algorithms. Combining the observable segregation of markers with that of QTL linked on the same chromosome is the basis of QTL mapping. In plants, QTL mapping depends on crossing experiments. In animals and humans, QTL mapping can be carried out with highly structured family data. The detected QTL represent genomic regions whose lengths depend on population type and sample size. This Primer unpacks the basics of QTL mapping with the goal of being accessible to audiences with limited statistical and genetic knowledge.