Evolution of quatitative characters Flashcards
Define a meristic character.
Those that are expressed as whole numbers.
Define a threshold trait.
A trait that is only expressed in the phenotype when the variable surpasses a threshold value.
The evolution of quantitative characters occurs under 3 types of selection. What are they?
- Directional
- Stabilising
- Disruptive
What happens in directional selection.
One point across the character distribution becomes favoured, thus selection moves towards this point and there is a shift in mean trait value.
In directional selection, does the point that becomes favoured have to be an extreme value?
No.
Directional selection is not often sustained in one direction. True or false?
True - fluctuations maintain variability.
We can describe directional selection with an equation. What is it?
R = h2s
R = selection response h2 = heritability s = selection differential
Define stabilising selection.
Intermediates of the trait are favoured and extremes are selected against.
What happens to the variance under stabilising selection?
There is a reduction in variance of distribution as only the middle values are selected for.
What happens to the mean under stabilising selection?
There is no change to the mean.
Define recruitment.
A natural increase in a population as progeny grow and new members arrive.
Define disruptive selection.
Extreme values are selected for and intermediates are less fit.
Under what conditions does disruptive selection usually occur?
Resource limitation where different phenotypes become specialised for different resources.
What happens to the variance in disruptive selection?
It increases the variance of distribution as the lower/upper limit values are extended.
Artificial selection has both a) direct and b) indirect responses. Give examples of each.
a) A change in the trait being selected for
b) Changes in related traits
