[18.3-4] natural selection, effects of selection on evolution Flashcards
1
Q
describe the core of natural selection?
A
- genetic diversity in a population due to random mutations (gene pool)
- ability to reproduce and pass on alleles (genes)
- selective pressures in the environment leads to differential survival
- those that have a selective advantage will be more likely to survive and reproduce, thus passing on advantageous alleles
- over many generations desired alleles will increase in frequency
2
Q
what are selection pressures?
A
environmental factors that limit the polulation of a species
3
Q
what are some examples of selection pressures? (3)
A
- predation
- disease
- competition
4
Q
what factors does the process of evolution by natural selection depend on?
A
- organisms produce more offspring than can be supported by the available supply of food, light, space etc.
- genetic variety within the populations of all species
- variety of phenotypes that selection operates against
5
Q
what are the 3 types of natural selection?
A
- stabilising
- directional
- disruptive
6
Q
draw the graph!
describe stabilising selection
A
- favours average phenotype (phenotype around the mean)
- selection against extreme phenotypes
- tends to occur where the environmental conditions are constant over long periods of time
7
Q
draw the graph!
describe directional selection
A
- changes phenotype of a popuation
- favours phenotypes that vary in one direction from the mean in the population ie. extreme phenotype
- due to change in environmental condition
8
Q
draw the graph!
describe disruptive selection
A
- favours individuals with extreme phenotypes rather than those with phenotypes around the mean of the population
- occurs when an environmental factor takes two or more distinct forms