Most of the important agronomic traits are quantitatively inherited and are controlled by several genes (i.e. polygenic). Thus, the nature of quantitative traits is that their expression is controlled by tens, hundreds or even thousands of quantitative trait loci (QTL), and in general, they are having only a small effect on the trait. QTL is a genomic region that comprises gene(s) which govern(s) the expression of the quantitative trait. Since the advent of molecular markers, researchers and breeders have aimed to identify functional markers (refer chapter x for different kinds of markers) associated with these QTL for implementation of marker-assisted selection. Historically, QTL detection started with linkage mapping in biparental populations (refer chapter x for population types). Identifying a gene or QTL within a plant genome is like finding the proverbial needle in a haystack. However, QTL analysis can be used to divide the haystack in manageable piles and systematically search them. In simple terms, QTL analysis is based on the principle of detecting an association between phenotype and the genotype of markers. Markers are used to partition the mapping population into different genotypic groups based on the presence or absence of a particular marker locus and to determine whether significant differences exist between groups with respect to the quantitative trait being measured. Thus, statistically a significant difference between phenotypic means of the marker groups (either 2 or 3), depending on the marker system and type of population, indicates that the marker locus being used to partition the mapping population is linked to a QTL controlling the trait.
KeywordsQuantitative Trait Locus Interval Mapping Quantitative Trait Locus Analysis Composite Interval Mapping Quantitative Trait Locus Effect
- Moser G, Muller E, Beeckmann P, Yue G, Geldermann H (1998) Mapping QTL in F2 generations of Wild Boar, Pietrain and Meishanpigs. In: Proceedings of the 6th world congress on genetics applied to livestock production, vol 26, Armidale, pp 478–481Google Scholar
- Broman KW (2001) Review of statistical methods for QTL mapping in experimental crosses. Lab Anim 30(7):44–52Google Scholar
- Doerge RW (2002) Mapping and analysis of quantitative trait loci in experimental populations. Nat Rev 3:43–53Google Scholar
- Hospital F (2009) Challenges for effective marker-assisted selection in plants. Genetica 136:303–310, http://www.knowledgebank.irri.org/ricebreedingcourse/bodydefault.htm#QTL_mapping.htm PubMedCrossRefGoogle Scholar
- Kang MS (2002) Quantitative genetics, genomics, and plant breeding. In: Papers from the symposium on quantitative genetics and plant breeding in the 21st century, Louisiana State University, 26–28 Mar 2001, CAB International 2002Google Scholar