structural:scholar_edition
QTL mapping

Many complex traits are genetically determined by quantitative trait loci (QTL). A Quantitative Trait Loci analysis can be used to find regions on the genome sequence that are associated with a complex trait. To find these regions, researchers will select a trait of interest and take a group of individuals of a species with varying expressions of this trait. They will label the individuals as founding parents and attempt to measure the trait. This can be difficult as most traits do not have a direct cut off point. Researchers will then genotype the parents using molecular markers such as SNPs or RFLPs. These act as signposts pointing to an area of where the genes associated with a trait are. From there, the parents are crossed to produce offspring. These offspring are then made to produce new offspring, but who they breed with can vary. They can either reproduce with their siblings, with themselves (different from asexual reproduction), or backcross. After this, a new generation is produced that are more genetically diverse. This is due to recombination. The genotype and phenotype of this new generation are measured and compared with the molecular markers to identify which alleles are associated with the trait. This does not mean there is a direct causal relationship between these regions and the trait, but it does give insight that there are genes that do have some relationship with the trait and reveals where to look in future research.