With the advent of modern genetics, scientist often try to investigate the under
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With the advent of modern genetics, scientist often try to investigate the underlying portions of the genome that influence quantitative traits. These portions are called Quantitative Trait Loci or QTLs. The way this is done is using QTL mapping, which is a suite of different computational techniques that uses a genetic ‘map’ to identify portions of the genome responsible for any given trait. One of the first QTLs identified was the one responsible for color in Monkey flowers. The above is the clade which contains multiple species of monkey flower, primarily organized by hummingbird pollinated or bee pollinated.
QTL Mapping results are often displayed as a LOD score. A LOD score measures the likelihood that a QTL near your marker is responsible for the trait in question. LOD scores increase the closer the association is between marker and QTL. Make sure you can explain exactly what a peak means in terms of finding a QTL.
In the above graphs, what exactly is being recombined in (a)? How do we know the location on the chromosome in (b)? Marker should be part of your answer.
3.5 Chromosome 10 3.0 -fruit mass -soluble-solids concentration 1.5 0.5 0.0 00 0.1 0.2 03 04 0.5 Recombination rate Location on chromosomeExplanation / Answer
QTLs or Quantitative Trait Loci are regions of DNA associated with a particular observable phenotype, a trait that can be measured. QTLs are genes which are either linked to the gene which controls a particular phenotype, or the QTL contains the gene contributing to that phenotype. Either way, a gene qualifies as a QTL only when it is inherited along with a specific phenotype, and hence acts as a marker of the presence of the gene responsible for that phenotype. QTLs are particularly helpful in case of a phenotypic feature which are continuous in nature, or in other words, traits which vary across a range of degrees (e.g. - height, complexion). Some phenotypic features are polygenic in nature, that is multiple different genes on different chromosomes might contribute to the same phenotype. In that case, a polygenic phenotype can have different QTLs on different chromosomes. QTL mapping is done by identifying the molecular markers (SNPs or microsatellites) that correlate with the observed phenotypic trait. QTL mapping reveals the location of the genes that are responsible for that phenotypic trait, after which these genes can be sequenced.
In graph 'a', the different phenotypes of monkey flowers are being recombined in order to test for the association of specific marker genes with phenotypic traits. Mimulus cardinalis is a red variety of monkeyflower which gets pollinated by hummingbirds and Mimulus lewisii is a pale-pink variety of monkeyflower that is pollinated by bumblebees. The marker used in the case of the QTL mapping of monkeyflowers is the YUP (Yellow Upper) gene. This marker is responsible for the presence of yellow carotenoid pigments in the pink monkeyflowers (Mimulus lewisii) or the absence of the same from the red variety monkeyflowers. The recombination between these two flower varieties led to the substitution of the YUP allele from one species to the other. The resulting effect of this recombination on pollination patterns revealed the association of the YUP allele with the QTL controlling flower colour and morphology.
The chromosome in which a specific QTL is present can be found by coarse mapping and fine mapping procedures. The objective of QTL analysis is to make use of marker genes with known loci to partition or segregate the mapping population to different genotypic classes, based on genotypes at the marker locus. The differences in the genotype (underlying the phenotypic trait in question) depending on the presence or absence of the marker goes on to reveal that the marker is linked to the QTL controlling the trait. Since the marker locus is known, therefore using that information the chromosomal location of the associated QTL can also be found, since the marker is correlated to the QTL controlling the phenotypic trait.
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