Lecture 4: Selection Flashcards
What would the heritability of a trait with no genetic variation be?
0.
Define ‘selection differential’ (S).
The selection differential is the difference of the base population mean and the mean of the selected parents.
Define ‘response to selection’ (R).
How much gain you make when mating the selected parents.
Related response to selection and selection differential.
R = h(squared) x S.
Define ‘phenotypic evolution’.
Change in the mean or variance of a trait across generation due to changes in allele frequencies.
Define ‘fitness’.
Relative transmission of alleles to the next generation.
How can you measure directional selection?
Linear regression.
Define ‘standardisation’ (z-scores).
Standardisation of phenotypic traits allows to interpret selection as a number of standard deviation from the mean.
How do you calculate a z-score?
The score minus the mean score, divided by the standard deviation.
How can you measure non-linear selection?
Quadratics.
Does a positive quadratic represent destructive or stabilising non-linear selection?
Destructive. (sad face)
Does a negative quadratic represent destructive or stabilising non-linear selection?
Stabilising. (smiley face)
Define ‘direct selection’.
Causalrelationshipbetweena
phenotypictraitandfitness.
Define ‘indirect selection’.
Covariancebetweenatraitandfitness
causedbyaphenotypiccorrelationbetweenthattrait
andanothertraitunderdirectselection.
What is stabilising selection?
Favours intermediate phenotype. There are no changes in the mean but a reduction in variance. It is expected to reduce genetic variation.
What is disruptive selection?
Favours both phenotypic extremes. There are no changes in the mean but a reduction in variance. it is expected to increase genetic variation.
