32. Measuring evolution Flashcards
How do we measure evolution?
Can’t actually measure evolution itself because a oftenly a phenotype is created by interaction of several genes → can only measure selection and deduce evolution by natural selection assuming the underlying genetics
What are the problems in using phenotypes in measuring evolution?
Not necessarily evolutionary but change in environment leads to favouring of a phenotype
What are the types of phenotypic selection?
- Stabilising selection
- Directional selection
- Diversifying selection
Explain stabilising selection
An intermediate phenotype is favoured over extremes
Explain directional sleection
Selecting the extreme in populations
Explain diversifying selection
Both phenotypic extremes are favoured over the intermediate
How to calculate selection differential S?
What are the possible mathematical measures for estimating selection?
- Selection differential (S)
- Heritability of a trait
- Additive genetic effect
What is a real life historical example of calculating selection differential?
A big storm on East coast in 1898 → sparrows started dying → brought to scientist Herman Bumpus → analysed survivors and non-survivors
Directional selection in males
Stabilising selection in females (no graph included in flashcards but there is in lecture slides)
=> Sexually antagonistic selection
Explain how heritability of a trait is calculated as a mathematical measure of estimating selection
Breeder’s equation
Explain heritability
(1) Trait value in offspring is positively correlated with the value in parents → high heritability (high resemblance)
(2) Trait values in offspring and parents are not correlated → low heritability (low resemblance)
Individuals vary because of environmental effects and genetic effects
What is the additive genetic effect? How it is calculated?
The additive effect is independent of the allele from the other partner (maternal can contribute +1 while paternal +2 towards the phenotype)
How is heritability evaluated (high / medium / low) in a graph?
What is adaptive radiation?
ADAPTIVE RADIATION - new species rapidly diversify from ancestor where each new species is adapted to utilise a specific unoccupied niche in the environment/resources
Members evolve different morphological features (adaptations) in response to the different selection pressures
Example - Galapagos finches
Natural selection on bill morphology graphs
Explain what is character displacement
Character displacement - competition between / within species leads to have different characteristics - less competition between each other
When competitors introduced - small beaks were favoured
What is coevolution?
Paired evolution if several species in the same environment
