Question

Help please

4. What is quantitative trait loci (QTL) analysis and how does it help us understand the genetics of phenotypic traits?

Answer 1

Quantitative traits are controlled by many genes, more than one gene determines the expression of a given trait hence it's called polygenic trait. Those of which regions in genome is associated with particular this type of quantitative phenotypic trait, are known as Quantitative Trait Locus Analysis (QTLs). It is a statistical method which can link both phenotypic(trait measurements) and genotypic(mostly molecular markers) data. Main purpose of QTL analysis is to find phenotypic difference and to explain genetic basis of variation in complex traits. Whether phenotypic differences are mainly due to few loci with large effects or to many loci with little effects. It indicates the proportion of the phenotypic variation. To analyse QTL, genetically different two or more strains of organisms are selected as a trait of interest. Specific genetic markers like SNPs, SSRs and RFLPs are selected for genotyping because these markers are unlikely to affect the trait of interest. To perform QTL analysis, parental strains are crossed, producing F1 heterozygous individuals and F1 individuals are crossed between each other. Phenotypes and genotypes of F2 are scored. Markers which genetically linked to QTL, it influences the trait of interest to segregate more frequently with trait values, show a significant association with the phenotype. Unlinked marker with trait of interest will not show any significant association with phenotype. QTL analysis helps in agricultural, medicinal field to link various phenotypes to a particular region of chromosomes. And interaction, number, precise location of this regions can also be identified by QTL analysis. Thus, by QTL analysis we can understand the genetics of phenotypic trait.