Evolution Flashcards
What is evolution?
-the change in frequency of different alleles
4 factors affecting the frequency of different alleles in a population?
- Natural selection
- Sexual selection
- Gene flow
- Chance
How does natural selection affect evolution?
-different rates of survival (and reproduction) because of the environment
How does sexual selection affect evolution?
-different phenotypes - hence genotypes being favoured for reproduction
What is gene flow?
-movement of large numbers of organisms into or out of a habitat
How does chance affect evolution?
-distribution of alleles might be by chance in a small population (genetic drift)
Factors related to population density
-competition
-communicable diseases
-predators
-parasites
Factors independent of population density
-climate
-natural disasters
-seasonal change
-human activities
Bottlenecks effect
-if population is reduced = alleles are reduced
-can take many generations for mutation to restore genetic diversity
Founder effect
-small no.of individuals colonise an area
-no.of alleles available is limited by the small gene pool
Beneficial mutation in a small gene pool
-increases the mutation in frequency
What is normal distribution?
-how we expect a characteristic to be spread through a population
-useful to spot evolutionary forces in action
What is stabilising selection?
-selection that tends to favour the norm/average
-reject the extremes
-eg. No.of offspring in a brood of eggs
Directional selection
-one extreme trait is favoured - those alleles become more frequent
-often seen in response to environmental change
-often sexual selection
Disruptive selection
-2 distinct extreme phenotypes are favoured
