Topic 19 - Populations and Evolution Flashcards
What is the Hardy-Weinberg principle?
A mathematical formula that can be applied to calculate the frequencies of the alleles.
What does the Hardy-Weinberg principle assume?
1) No mutations arise.
2) Population is isolated, no flow of alleles in or out.
3) No selection.
4) Population is large.
5) Mating within population is random.
What are the two equations of the Hardy-Weinberg principle?
Allele frequency = p + q = 1
p = frequency of dominant allele (A)
q = frequency of recessive allele (a)
Genotype frequency = p^2 + 2pq + q^2 = 1
p^2 = frequency of AA
2pq = frequency of Aa
q^2 = frequency of aa
What is phenotypic variation a combination of?
Genetic and environmental factors.
What are the causes of genetic variation
- Mutations
- Meiosis
- Crossing over
- Independent segregation
- Random fertilisation
What is hard to figure out between genetic and environmental influences?
Hard to distinguish between the two effects on variation so conclusions must be drawn with care.
What does the process of evolution by natural selection depend on?
1) Organisms produce more offspring than can be supported (over-production).
2) Genetic variation present in population.
3) Phenotypic variation within population.
4) Environmental factor (predator, disease, competition etc) results in differential survival and reproduction of individuals.
How does reproductive success affect allele frequency?
1) Organisms produce more offspring than can be supported.
2) Intraspecific competition keeps population relatively constant in size.
3) Random mutation of alleles within gene pool means some individuals will possess combination of alleles that make them more likely to survive.
4) These individuals have a better chance of reproducing and producing more offspring.
5) They will pass on their advantageous alleles to the next generation.
6) This means the favourable alleles gave the parents a selective advantage.
7) Offspring are also more likely to survive and pass on these advantageous alleles.
8) Over many generations, the frequency of the favourable alleles in the population increase, whilst the frequency of the less favourable allele decreases.
What is directional selection?
Change in a population from one phenotype to another.
What is stabilising selection?
A reduction of variation about an optimum modal value.
What is a disruptive selection?
Favours extreme phenotypes at the expense of intermediate phenotypes.
- Occurs when environmental factors takes two or more distinct forms.
- Can lead to formation of two separate species.
What is a species?
A group of organisms that can interbreed and produce living fertile offspring.
What is speciation?
1) Individuals of a species can interbreed in the same area.
2) Habitat separates into two regions that becomes geographically isolated.
3) Abiotic and biotic conditions within two areas become different so selection pressures exist in two areas.
4) Within a population, there is genetic variation cuz gene mutation.
5) Mutations give rise to different phenotypes.
6) Organisms with phenotypes better able to survive are selected for, meaning they have greater reproductive success and pass on their alleles.
7) Over time, the differences between gene pools become so great that the two populations can no longer interbreed and produce living fertile offspring - speciation!
What is genetic drift?
The change in allele frequencies due to chance events. It occurs in small populations because chance plays a bigger role.
In smaller populations, the few members possess a smaller variety of alleles and have low genetic diversity.
What is a genetic bottleneck?
Sharp reduction in size of population, some alleles may be lost. Allele frequency thus changed.
