Editing Quantitative trait locus (section)

==Definition==
A '''quantitative trait locus''' ('''QTL''') is a region of [[DNA]] which is associated with a particular [[Phenotype|phenotypic]] [[Trait (biological)|trait]], which varies in degree and which can be attributed to [[polygene|polygenic]] effects, i.e., the product of two or more [[gene]]s, and their environment.<ref name="ComplTraitCons">{{cite journal |author1=Oduola Abiola |display-authors=et al |title=The nature and identification of quantitative trait loci: a community's view |journal=[[Nature Reviews Genetics]] |publisher=[[Nature Portfolio]] |date=2003 |volume=4 |issue=11 |pages=911–916 |doi=10.1038/nrg1206 |pmid=14634638 |pmc=2063446 |s2cid=27285742}} {{S2CID|195367115}}.</ref> These QTLs are often found on different [[chromosomes]]. The number of QTLs which explain variation in the phenotypic trait indicates the [[genetic architecture]] of a trait. It may indicate that plant height is controlled by many genes of small effect, or by a few genes of large effect.{{cn|date=July 2024}}

Typically, QTLs underlie continuous [[Trait (biological)|trait]]s (those traits which vary continuously, e.g. height) as opposed to discrete traits (traits that have two or several character values, e.g. red hair in humans, a recessive trait, or smooth vs. wrinkled peas used by [[Gregor Mendel|Mendel]] in his experiments).

Moreover, a single [[Phenotype|phenotypic]] trait is usually determined by many genes. Consequently, many QTLs are associated with a single trait.
Another use of QTLs is to identify [[candidate gene]]s underlying a trait. 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, this task being fundamental for marker-assisted crop improvement.<ref>{{cite journal |last1=Watanabe |first1=Satoshi |last2=Hideshima |first2=Rumiko |last3=Xia |first3=Zhengjun  |display-authors=etal|title=Map-Based Cloning of the Gene Associated With the Soybean Maturity Locus E3 |journal=Genetics |date=2009 |volume=182 |issue=4 |pages=1251–1262 |doi=10.1534/genetics.108.098772|pmid=19474204 |pmc=2728863 }}</ref>