Quantitative trait loci (QTL) mapping for Crop Improvement

Chromosome segments controlling quantitative traits are called as quantitative trait locus/loci (QTL). A QTL is defined as a region of the genome that is associated with an effect on a quantitative trait. These traits are controlled by multiple genes, each segregating according to Mendel's laws. These traits can also be affected by the environment to varying degrees. QTL mapping can enumerate genes contributing to a trait and estimate their relative importance. With the advent of molecular DNA markers, several QTL mapping studies have been carried out successfully in diverse crop species. However, it requires a combination of modern molecular genetics techniques and powerful statistical methods which is sometimes difficult to understand. There are many factors that influence QTL mapping such as population size and type, level of replication of phenotypic data, environmental effects and genotyping errors. Keeping this in mind, this review is written to highlight the basic concept behind QTL mapping, process of QTL detection, its importance and its application in overall crop improvement.