2pq
Heterozygous
Hardy Weinberg equation?
P^2 + 2pq + q^2 = 1.0
P + q = 1.0
What is the hardy Weinberg principle?
Mathematical equation that can be used to calculate the frequencies of the alleles of a particular gene in a population.
What does the hardy Weinberg principle assume that?
- No mutations arrive.
- Large population.
- Mating within the population is random.
- There is no selection.
- Population is isolated.
What does genetic variation arise as a result of?
Mutations
Meiosis
Random fertilisation of gametes
What does natural selection depend upon?
- Genetic variety within the population.
- A variety of phenotype that selection operates against.
- Organisms produce more offspring than can be supported by the available resources.
Gene pool
Total number of all the alleles of all genes of all individuals within a particular population at a given time.
When does disruptive selection occur?
When an environmental factor takes two or more distinct forms.
What does disruptive selection favour?
Favours those with extreme phenotype.
What does stabilising section favour?
The average phenotypes.
What does directional stabilising selection favour?
Favours phenotypes that vary in one direction from the mean of the population.
Speciation
Evolution of a new species from an existing one.
Adaptive radiation
Each phenotypes present will be subject to selective pressures that will lead to populations becoming adapted to its local environment.
What type of population does genetic drift occur in?
Small
Why does genetic drift occur in small populations?
Less genetic diversity. Genetic diversity is restricted to few alleles. As small number, not an equal chance of them all being passed on. Those passed on will quickly affect whole population as the frequency is high. Any mutation to one of these alleles that is selectively favoured will also quickly affect the population as the frequency is high.
Two types of speciation.
Allopatric
Sympatric
Describe the process of allopatric speciation.
- Two populations become geographically separated.
- Environmental conditions may differ on either side of the barrier. Therefore, natural selection will affect both populations differently.
- Over many generations this may lead to reproductive separation and the formation of separate species.
Describe the process of sympatric speciation.
- Occurs between populations of species within the same area.
- Occurs when random mutations within a population prevent individuals that carry the mutation from breeding with other members of the population that don’t carry the mutation.
What are the changes that results in reproductive isolation?
- Seasonal change. (Different flowering or mating patterns).
- Mechanical change. (Changes in size and shape).
- Behavioural changes. (Group of individuals may develop courtship rituals that aren’t attractive to the rest of species).
What is the advantage of presenting results as a ratio?
Comparisons can be made.
Number/ sample size may vary.
