Quantitative trait locus

Quantitative trait locus (QTL) is a region of DNA that is associated with a particular trait (e.g., plant height). Though not necessarily genes themselves, QTLs are stretches of DNA that are closely linked to the genes that underlie the trait in question.

Related Topics:
DNA - Trait - Gene

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Typically, QTLs underlie continuous traits (those traits that vary continuously - the trait could have any value within a range - e.g., height) as opposed to discrete traits (traits that have two or several character values - e.g., number of leaves on a plant or smooth vs. wrinkled peas used by Mendel in his experiments).

Related Topics:
Trait - Mendel

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Moreover, a single phenotypic trait is usually determined by many genes (a phenomenon called epistasis). Consequently, many QTLs are associated with a single trait - these QTLs can even be found on different chromosomes. Knowing the number of QTLs that explains variation in the phenotypic trait tells us about the genetic architecture of a trait. It may tell us that plant height is controlled by many genes of small effect, or by a few genes of large effect.

Related Topics:
Epistasis - Chromosomes - Genetic architecture

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Another use of QTLs is to identify candidate genes (Quantitative Trait Genes, QTG) underlying a trait. Once a region of DNA is identified as contributing to a phenotype, it can be sequenced. The DNA sequence of any genes in this region can then be compared to a database of DNA for genes whose function is already known. In this way, we might find a gene involved in the production of growth hormone.

Related Topics:
Quantitative Trait Gene - Sequenced

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In a recent development, classical QTL analyses are combined with gene expression profiling i.e. by DNA microarrays. Such expression QTLs (e-QTLs) describe cis- and trans-controlling elements for the expression of often disease-associated genes. Observed epistatic effects have been found beneficial to identify the QTG by a cross-validation of genes within the interacting loci with metabolic pathway- and scientific literature databases.

Related Topics:
DNA microarray - Cis - Trans - Epistatic effects - Metabolic pathway - Scientific literature

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