Quantitative Genetics Flashcards
What are most genetic traits (discontinuous or continuous variation) that have been studied?
Discontinuous variation
What are discontinuous variation?
- Distinct categories
- Tend to be qualitative
- Controlled by a few genes
- Unaffected by the environment
What are continuous variations?
- No distinct categories
- Tends to be quantitive
- Controlled by a lot of genes
- Strongly influenced by the enviroment
What is quantitative genetics?
The study of continuously measured traits (such as height or weight) and their mechanisms.
What are three types of polygenic traits?
- Metric
- Meristic
- Threshold
What are the types of polygenic traits based on?
Theoretical assumption of an underlying normal distribution
What is metic?
Continuous scale
What is meristic?
Discrete scale
What is threshold?
Present or absent
What are different types of metric traits?
- Mean
- Popluation variance
What is mean?
The central of phenotypic distribution
What is population variance?
The average squared deviation from the mean is called the variance
Why is quantitative genetics important?
- Medicine
- Agriculture
- Conservation
How is quantitative genetics important for medicine?
- Susceptibility to disease
- Complex disorders caused by multiple genetic and environmental factors
- Understanding genetic vs environmental causes
- Prevention
- Genetic counselling
- Genetically-tailored treatments
How is quantitative genetics important for agriculture?
- Economically important traits = quantitative traits.
- Quantitative genetics theory and the basis for selective breeding
- Environmental variation reduces efficiency of selection
How is quantitative genetics important for conservation?
Conservation of:
- endangered species
- captive breeding programmes
Consequences of inbreeding and outcrossing.
Are quantitative genetics fundamentally different from the Mendelian patterns of inheritance that you have been studying previously?
NO …traits are still determined by alleles of genes that are inherited following the laws of segregation and independent assortment
BUT …now we must consider traits that are influenced by many genes and are also influenced by the environment
Finish:
Phenotype =…
genotype + environment
What is the variation in population related to?
Vp = VG + VE + VGE
What does VP stand for?
Phenotypic Variation
What does VG stand for?
Genetic variance
What does VE stand for?
Environmental variance
What does VGE stand for?
Genetic x environmental interaction variance
What can phenotypic variation in a trait be?
Partitioned
How can VG be partitioned into variation?
- Alleles present or additive effects (VA)
- Dominance interaction (VD)
- Epistatic interactions (VI)
What is the VG equation?
VG = VA + VD + VI
What is additive effect?
Effect of adding alleles
What is dominance interaction?
Two alleles at the same locus
What is epistatic interaction?
Alleles at different locus
What is Genetic variance [VG]?
Contribution to phenotypic variation due to set of alleles present in a population and their interactions
What is Environmental variance [VE]?
Contribution to phenotypic variation caused by differences in environmental conditions (E for environment)
What is broad sense heritability?
Measures the importance of genetic variation (VG) relative to total variation (VP) in the phenotype
What is the equation for broad sense heritability?
H^2 = VG/VP
What is heritability of trait?
Describes how much variation is genetic
What is narrow sense heritability?
Measures the importance of additive genetic variation (VA) or variation due to the alleles present in the population, relative to total variation (VP) in causing variation in the phenotype.
What is the equation for narrow sense heritability?
H^2 = VA/VP
What should the theoretical H^2 vary between?
0 and 1
What does H^2 estimate?
Predict change in the population mean under selection
Finish the sentence:
When H^2 increases, the response to…
selection increases
Relating to y = mx + c what is h^2 equal to?
M
What is the infinitesimal model?
A simple model of the inheritance of quantitative traits, which assumes an infinite number of unlinked loci, each with an infinitesimal effect
Finish the sentence:
Infinite number of genes controlling a …..
phenotypic trait each with a very small effect
