What is QTL?
Number of agronomically important traits – yield, quality, maturity, resistance to biotic and abiotic stress are the results of the interaction of number of gene loci called Quantitative Trait Loci, display a large continuous range of variations forming a Normal bell shaped curve., hence can’t be fitted to simple Mendelian ratio.
Principal of Mapping of QTLs
Associate QTLs with molecular markers in their common inheritance and to assign individual QTL to a chromosome location and determine the alleles contributed by each parents.
Method of QTL Mapping
- QTL mapping in biparental mapping population is done using ANOVA and linear regression analysis to test the relationship between traits and markers.
- QTL mapping using simple interval mapping method (SIM) – It considers the linkages between markers and uses the maximum likelihood equation to give an estimate, based on the LOD (logarithm of odds) threshold score, of the probability of a QTL being present in any interval based on flanking marker information.
- QTL mapping using composite interval mapping method (CIM) – It combines SIM for a single QTL in a given interval with multiple regression analysis on markers associated with other QTL, there by enabling mapping of multiple QTLs along with increased precision and power of detection.
- QTL mapping using multiple interval mapping method (MIM) – It is an extension of SIM, allowing the detection of multiple QTL and positing QTLS between markers. It can be also used to detect epistatic interactions.
- Other method of QTL mapping – MCML – Monte Carlo Maximum Likelihood or Bayesian; and MCIM – Mixed Model composite interval mapping.
Softwares used for QTL mapping
- QTL Cartographer
- QTL Mapper