Lecture 13 Flashcards
Continuous traits are a result of multifacorial inheritance. What does this mean?
- Many genes/loci are involved
- Variance is introduced by the environment
- Variance introduced by the genetic backgrounds (epistasis)
Epistasis:
The interaction of genes that are non alleles, such as the suppression of one gene by another
- Genetic and environmental interactions
Quantitative genetics as opposed to traditional mendelian genetics:
- Explain the genetic basis of continuous complex/multifactorial/quantitative traits
- Make no assumptions
- Focus on a populations
- Statistical and mathematical
Genetic architechture:
- How much variation is genetically based
- How many genes are involved
- Where are the genes found in the genome
- What are the genes underlying the QTLs?
How much variation is explained by genetic factors?
- Observe a phenotype to infer genetic causes (forward genetics)
- Focuses primarily on the genes inducing variation on those fundamental to a function
Reverse genetics:
- Create genetic perturbation (mutations, insertions, transpositions) and observes the effects of these changes
- Decompose into linear effects
- Decomposing data into additive (alpha) and dominance (delta) effects
- The effects are linear and therefore independent from each other
- Variation calculation:
- alpha of the AA genotype and the + alpha of the BB genotype and compute a residual/environmental variance sigma squared based e of what is left unexplained
Heritability:
H squared = sigma squared to the base G/ sigma squared to the base P
The fundamental components of measuring how much variation is explained genetically
- The population size and properties
- Accurate measure of the mean/means for the different genetic classes
- A good estimation of the variance for its different componenets
How many loci are involved?
- Observe the covariance between parents and offspring
- Interactive QTL mapping is a straightforward frame work
- Use the change of variance between parents and offspring
- Assume that all the effects are of equal size and all the effects from one parent go in the same direction
- Mean of the parents minus the mean of the other parent
- The rate of convergence to the parents value is proportional to the number of QTL affecting the trait (if many genes are involved the segregating offspring it will take more time to return to the parent)
- Using molecular markers, a step-wise inclusion of WTL to the model:
- Describes the iterative procedure of the WTL mapping strategy
- Find the first significant alpha and include the sum of G
QTL are classified into major, minor QTL and infinitesimal/polygenic effects (infinite number of very small effects)
- We will never have the ability to measure these tiny tiny infinite effects
The power to detect QTL depends on:
- sample size (to gain precise estimate of the variance components)
- the size of the effect/penetrance of the genetic effect