QTL kartlegging i planter Flashcards
The following histogram shows the phenotypic distribution of the quality trait «Particle Size
Index» in what flour in F2 from a cross between the wheat cultivars Falcon and Heron. What
does this phenotypic distribution tell us about the genetics behind the trait? How many genes
are involved? Is dominance involved?
The distribution in F2 is 1:2:1. This implies that there’s mainly one gene controlling the trait, and
that dominance isn’t involved.
Compare QTL mapping based on linkage analysis with association mapping. Which method
requires the highest number of markers to identify the QTL behind the trait?
QTL mapping is used to localize the genes affecting a quantitative trait, and using linkage analysis between marker and gene. The statistical association between a marker and a gene depends on both distance and the effect the gene has on the phenotype
Association mapping seeks to identify specific functional genetic variants (loci, alleles) linked to phenotypic differences in a trait to facilitate detection of trait causing DNA sequence polymorphisms and selection of genotypes that closely resemble the phenotype.
Association mapping requires a higher number of markers because the method relies on
historical recombination between marker and QTL.
What is the difference between genetic distance versus physical distance?
Genetic distance: Measured as recombination frequency.
Physical distance: Number of base
pairs distance.
What are the greatest limitations for QTL mapping in a RIL population compared to GWAS?
In QTL mapping we are limited to map genes/regions that show allelic variation between two
parents only. The genetic diversity of a GWAS panel is usually much larger with the potential to map
a larger number of QTL.
Another limitation of QTL mapping is the limited recombination happening as a result of one cross,
compared to all the historical recombination events in a GWAS population. The genetic resolution is
lower in a QTL mapping population. GWAS has a higher precision when it comes to the localization
of the QTL due to the historical recombination events.
What is GWAS
Genome-wide association studies (GWAS) help scientists identify genes associated with a particular disease (or another trait). This method studies the entire set of DNA (the genome) of a large group of people, searching for small variations, called single nucleotide polymorphisms or SNPs
What is a quantitative trait?
Traits governed by multiple loci with additive effects. A quantitative trait is a measurable phenotype that depends on the cumulative actions of many genes and the environment. Examples of quantitative traits include height, skin colour, weight and blood pressure.
What are markers used for?
Measurable variation in the DNA – can be used to mark genetic differences between individuals. It is used to Study genetic variation, Construct linkage maps and map genes (QTL mapping) and as a Selection tool in plant breeding (marker assisted selection, genomic selection).
Markers have to be polymorphic to provide information which can be used for mapping.
Codominant markers can be used to identify heterozygous individuals
