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Reference.org
Quantitative trait locus
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<p> A quantitative trait locus (QTL) is a <a href="/facts/Locus_(genetics)/JcIT8wLm">locus</a> (section of <a href="/facts/DNA/nB89Iauz">DNA</a>) that correlates with variation of a <a href="/facts/Quantitative_trait/l6HY9lPG">quantitative trait</a> in the <a href="/facts/Phenotype/vxWXKGLj">phenotype</a> of a <a href="/facts/Population_genetics/v55qAnKu">population</a> of <a href="/facts/Organism/j8JkL09u">organisms</a>. QTLs are mapped by identifying which molecular markers (such as <a href="/facts/Single-nucleotide_polymorphism/Qy5Y2wom">SNPs</a> or <a href="/facts/Amplified_fragment_length_polymorphism/y1yGBvm2">AFLPs</a>) correlate with an observed trait. This is often an early step in identifying the actual <a href="/facts/Gene/e1swwPY6">genes</a> that cause the trait variation. </p>