Lecture Nine - Evolution

Question 1

What do evolutionary processes have an effect on?

Answer 1

The effect that a changing environment has on a population (or a species as a whole) depends heavily on evolutionary processes.

Question 2

What causes evolution?

Answer 2

Random events:
Stochastic, unpredictable, changes in allele frequencies across generations due to chance factors.

Non-random events:
Some alleles will confer either an advantage or a disadvantage on a ‘phenotype’ or trait, relative to the other alleles in the population.
Advantageous alleles should increase in frequency in the population over generations. Disadvantageous alleles should decrease in frequency over generations.

Question 3

What is directional selection?

Answer 3

Directional selection:
Two formes -
1) Purifying (negative) eliminates detrimental phenotypes (and alleles) from the population.
Involves individuals with the harmful allele dying before reproduction.
Decreases the frequency of this allele.
2) Positive (Darwinian) selection involves an increase in a particular alleles frequency over generations.
Beneficial alleles have a competitive advantage within the population - the confer phenotypes that are competitively superior - individuals with these phenotypes are more likely to reproduce the others in the population.

Question 4

What is domestication?

Answer 4

A form of evolution under positive selection.
In nature, evolution occurs by ‘natural selection.’
When humans do the selecting, we call it ‘artificial selection.’

Question 5

What is disruptive selection?

Answer 5

Directional selection, but favours alleles for phenotypes at BOTH ends of the continuum.

Question 6

What is balancing selection?

Answer 6

Maintins genetic variation.
Main form is selection on the heterozygote.
Heterozygote advantage - when heterozygotes out perform homozygotes.