Mapping of Quantitative Trait Loci (qtl)

What is a QTL? A Quantitative Trait Locus a region of the genome that is associated with an effect on a quantitative trait. Conceptually, a QTL can be a single gene, or it may be a cluster of linked genes that affect the trait. Using the methods for QTL detection to be discussed below, it is not possible to resolve the difference, and use the term “locus” to refer to a chromosomal region. Are QTL structural enzyme genes, do they code for regulators of gene expression, or are they non-coding regions that affect gene expression? The fact is, not known, and it is not possible to distinguish these possibilities based on the following methods. However, any of these are possible. The major purpose of QTL mapping is primarily to describe the effects of each genomic region on quantitative traits of interest, namely: 1. Detect which regions of the genome that affect the trait: where are the QTL? 2. Describe the effect of the QTL on the trait: How much of the variation for the trait is caused by a specific region? What is the gene action associated with the QTL additive effect? Dominant effect? Which allele is associated with the favorable effect? 3. Assign breeding values to lines or families based on their genotypes at one or more QTL. In this way the information obtained can be used in QTL mapping experiments for applied marker-assisted breeding strategies.