20.5 Evolution Flashcards
What is stabalising selection? (2 marks)
Environment stays stable
So the same alleles are selected in successive generations
Nothing changes
What is directional selection? (3 marks)
Change in environment
Change in selection pressures on the population
Different alleles are selected for successive generations
So genetically determined characteristics change
What is meant by a ‘genetic bottleneck’? (3 marks)
When a large number of the original population die (due to natural selection)
This leads to some alleles being lost
So when the now smaller population reproduces, the new population is a lot less genetically diverse.
Is genetic drift caused by natural selection or by chance? (1 mark)
Chance
Is a genetic bottleneck caused by natural selection or by chance? (1 mark)
Natural selection
What is meant by ‘genetic drift’? (1 mark)
A change in the gene pool is caused by chance instead of natural selection.
Why are species on islands more susceptible to genetic drift? (2 marks)
They have small populations.
They are geographically isolated from other members of their species.
Describe how genetic drift can contribute to extinction. (2 marks)
Genetic drift causes a reduction in genetic variation.
The species may have a reduced ability to survive in the new environment.
This can lead to extinction.
Describe how genetic drift can lead to the development of a new species. (3 marks)
Genetic drift causes a reduction in genetic variation.
The species may have a reduced ability to survive in the new environment.
So the population adapts.
This can lead to the development of a new species.
What does the Hardy-Weinberg principle state? (2 marks)
In a stable population with no disturbing factors, the allele frequencies will remain constant from one generation to the next and there will be no evolution.
What is the equation for the Hardy-Weinberg principle? (1 mark)
p^2 +2pq +q^2 = 1
What does ‘p’ mean in the Hardy Weinberg principle equation? (1 mark)
The frequency of homozygous dominant genotype in the population.
What does ‘q’ mean in the Hardy Weinberg principle equation? (1 mark)
The frequency of heterozygous genotype in the population.
What does ‘2pq’ mean in the Hardy Weinberg principle equation? (1 mark)
The frequency of homozygous recessive genotype in the population.
What is the difference between genetic diversity within a species and genetic diversity between species? (2 marks)
Within species: diversity between alleles
Between species: diversity between genes
