Summary
Regions of the genome statistically associated with variation in continuous traits.
In depth
QTL mapping associates genetic markers with variation in a trait across crosses or populations. It identifies regions of the genome, not necessarily genes. Many QTL have small effects, and resolution is improved by fine mapping.
QTL are used in crop and livestock breeding for yield and disease resistance.
Mapping crosses two inbred lines that differ in a trait, genotypes the F2 progeny at many markers and finds markers whose alleles correlate with the trait. The LOD score (log of odds) measures the strength of evidence, and a score above 3 is conventionally significant.
QTL work has helped breeders: genes controlling grain size in rice (GS3), fruit size in tomato (fw2.2) and maize domestication (teosinte branched1) came from QTL mapping. Fine mapping, sequencing and gene editing then identify the actual gene.
Key idea: QTL studies tell us how many regions affect a trait and how large the effects are, even when the genes are unknown.
Frequently asked questions
What is Quantitative Trait Loci?
Regions of the genome statistically associated with variation in continuous traits.
Which area of biology covers Quantitative Trait Loci, and how advanced is it?
Quantitative Trait Loci is one of the 54 topics in Genetics. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Polygenic Inheritance, Genome-Wide Association Studies, Genetic Linkage Mapping.
Can you give an example of Quantitative Trait Loci?
QTL for flowering time in maize.
What should I learn before Quantitative Trait Loci?
Work through the Beginner topics in Genetics first, such as Heredity, Gene, Allele, then return to Quantitative Trait Loci. Advanced topics assume the Intermediate vocabulary.
What topics are related to Quantitative Trait Loci?
The closest topics to Quantitative Trait Loci are Polygenic Inheritance, Genome-Wide Association Studies, Genetic Linkage Mapping, Gene Pool. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Quantitative Trait Loci?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Quantitative Trait Loci. To practise the whole of Genetics, use the Genetics quiz.
How is Quantitative Trait Loci different from Polygenic Inheritance?
Quantitative Trait Loci: Regions of the genome statistically associated with variation in continuous traits. Polygenic Inheritance: A trait controlled by many genes producing continuous variation, such as height and skin colour. Read both side by side and note what each one explains.
How should I study Quantitative Trait Loci step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Polygenic Inheritance and explain the difference aloud. Finally, take the Genetics quiz and come back to this page for any question you miss.