Interval Mapping
Lander and Botstein developed interval mapping, which overcomes the three disadvantages of analysis of variance at marker loci. Interval mapping is currently the most popular approach for QTL mapping in experimental crosses. The method makes use of a genetic map of the typed markers, and, like analysis of variance, assumes the presence of a single QTL. Each location in the genome is posited, one at a time, as the location of the putative QTL....
The term ‘interval mapping’ is used for estimating the position of a QTL within two markers (often indicated as ‘marker-bracket’). Interval mapping is originally based on the maximum likelihood but there are also very good approximations possible with simple regression.
The principle for QTL is: 1) The Likelihood can be calculated for a given set of parameters (particularly QTLeffect and QTL position) given the observed data on phenotypes and marker genotypes. 2) The estimates for the parameters are those were the likelihood are highest. 3) The significance can be tested with a likelihood ratio test
CONVENTIONAL methods for the detection of quantitative trait loci (QTLs) are based on a comparison of single QTL models with a model as- suming no QTL. For instance in the “interval map- ping” method (LANDER and BOTSTEIN 1989) the like- lihood for a single putative QTL is assessed at each location on the genome. However, QTLs located else- where on the genome can have an interfering effect. As a consequence, the power of detection may be compromised, and the estimates of locations and effects of QTLs may be biased (LANDER and BOTSTEIN 1989; KNAPP 1991). Even nonexisting so-called “ghost” QTLs may appear (HALEY and KNOTT 1992; MARTINEZ and CURNOW 1992). Therefore, it is obvious that multiple QTLs could be mapped more efficiently and more accurately by using multiple QTL models
Read more about this topic: Mapping Of Quantitative Trait Loci
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