Lectures 36/37-Quantitative genetics Flashcards
What is quantitative genetics?
To understand quantitative characters which are those where there are a range of possible values rather than categorical values
What is the phenotypic variation of a character?
Something which is usually distributed unimodally with a statistical description being done by mean and variance
What is the variation observed in quantitative characters?
They have continuous variation and high environmental variance compared with genotype differences
They also undergo polygenic inheritance where the additive effect and multigenic genes effect may be present
How is it possible to determine if continuous phenotypic variability is due to additive effects or the environment acting on the 1-gene 2 allele system?
This can be determined through raising offspring in a constant environment where the trait will show a less continuous distribution with different distributions for each phenotype if it is the environment acting on the 1 gene 2 allele system, while if the trait is determined by additive effects of many genes then a continuous variation will still be achieved
What are the different types of selection that can occur on quantitative traits?
Stabilizing which reduces variation
Directional selection which results in a change in the mean trait value
Disruptive which separates one distribution into two
Artificial selection which is typically done by a truncation selection
What is the selection differential?
The difference between meant trait value for selected parents and unselected population
How can testing for heritability be done?
Mate individuals at the extremes of the distribution and raise the offspring in a common controlled environment
The difference in means of the offspring and general population indicate heritability
What components can phenotypic variance be partitioned into?
Phenotypic Variance= Genetic variance + Environmental variance
Genetic Variance= Additive genetic variance + dominance variance
What is the difference between broad and narrow heritability?
Broad heritability is the degree to which phenotypic variation is due to genetic factors
(Genetic Variance/Phenotypic Variance)
Narrow heritability is the degree to which the phenotypic variation is due to additive genetic factors
(Additive genetic variance/phenotypic variance)
How can an estimate of narrow heritability be determined?
The parent-offspring phenotype relationship where the offspring value is compared to midpoint of the parent value where the slope will provide the estimate
What is the selection response?
Difference between mean trait value of offspring and previous generation
Response= narrow heritability*diferential
What is association mapping?
When a gene of phenotypic significance is detected through statistical analysis of markers which vary throughout the population allowing some insight to be gained as to the location of the gene and can be used to predict what allele for that gene locus the organism possess
What are typical markers?
Chromosome Bands External Phenotype Biochemical traits SNPs RFLPs Simple Sequence repeats
What is quantitative trait loci?
A breeding and statistical technique which estimates what fraction of a quantitative trait is due to a genetic marker
Note large associations of a trait with a marker may not result in a hugely valuable predictable value due to the multigenic nature of many traits
What are population association studies?
Genome wide studies of associations between markers and traits performed where selective breeding experiments are not possible so statistical analysis and family data can be used instead
