LOCATION OF QUANTITATIVE GENES ON CHROMOSOME-QTL
Quantitative trait locus (QTL) analysis is a statistical method that links two types of information—phenotypic data (trait measurements) and genotypic data (usually molecular markers)—in an attempt to explain the genetic basis of variation in complex traits
Molecular markers are preferred for genotyping, because these markers are unlikely to affect the trait of interest. Several types of markers are used, including single nucleotide polymorphisms (SNPs), simple sequence repeats(SSRs, or microsatellites), restriction fragment length polymorphisms (RFLPs), and transposable element positions.
In QTL analysis, the parental strains are crossed, resulting in heterozygous (F1) individuals, and these individuals are then crossed using either selfing/backcross/testcross.
The phenotypes and genotypes of the derived (F2) population are scored.
Markers that are genetically linked to a QTL influencing the trait of interest will segregate more frequently with trait values (large or small egg size in our example), whereas unlinked markers will not show significant association with phenotype.
Small sample sizes may fail to detect QTL of small effect and result in an overestimation of effect size of those QTLthat are identified. This is known at the "Beavis effect.
QTL studies require very large sample sizes, and they can only map those differences that are captured between the initial parental strains.
Because these strains are unlikely to contain segregating alleles of large effect at every locus contributing to variation in natural populations, some loci will remain undetected.
Quantitative trait locus (QTL) analysis is a statistical method that links two types of information—phenotypic data (trait measurements) and genotypic data (usually molecular markers)—in an attempt to explain the genetic basis of variation in complex traits
Molecular markers are preferred for genotyping, because these markers are unlikely to affect the trait of interest. Several types of markers are used, including single nucleotide polymorphisms (SNPs), simple sequence repeats(SSRs, or microsatellites), restriction fragment length polymorphisms (RFLPs), and transposable element positions.
In QTL analysis, the parental strains are crossed, resulting in heterozygous (F1) individuals, and these individuals are then crossed using either selfing/backcross/testcross.
The phenotypes and genotypes of the derived (F2) population are scored.
Markers that are genetically linked to a QTL influencing the trait of interest will segregate more frequently with trait values (large or small egg size in our example), whereas unlinked markers will not show significant association with phenotype.
Small sample sizes may fail to detect QTL of small effect and result in an overestimation of effect size of those QTLthat are identified. This is known at the "Beavis effect.
QTL studies require very large sample sizes, and they can only map those differences that are captured between the initial parental strains.
Because these strains are unlikely to contain segregating alleles of large effect at every locus contributing to variation in natural populations, some loci will remain undetected.
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