Evolution Flashcards
What is a gene pool?
The sum of all genes in a population
What is allele frequency?
The relative frequency of an allele in a population at any given time
What 2 equations make up the Hardy-Weinberg Principle?
- p + q = 1, 2. p² + 2pq + q² = 1
What does evolution involve in terms of alleles?
A long-term change in the allele frequencies within a population
What is p in the Hardy-Weinberg equation?
Frequency of dominant allele
What is q in the Hardy-Weinberg equation?
Frequency of recessive allele
What is p squared in the Hardy-Weinberg equation?
Frequency of homozygous dominant allele
What is 2pq in the Hardy-Weinberg equation?
Frequency of heterogeneous genotype in the population
What is q squared in the Hardy-Weinberg equation?
Frequency of homozygous recessive genotype in the population
What 5 assumptions underpin the Hardy-Weinberg principle?
- No selection 2. No mutation 3. No emigration/immigration 4. Random mating 5. Large population
What does the Hardy-Weinberg principle state?
That allele frequencies in a population should remain constant unless one or more factors cause those frequencies to change
Do populations tend to follow the Hardy-Weinberg principle in the real world? Why/why not?
No as the conditions/assumptions rarely tend to be met
What 2 things can the Hardy-Weinberg equations be used to calculate?
Allele and genotype frequencies
What is genetic drift?
Change in allele frequency caused by random mutations and chance
Why is a large population assumed for the Hardy-Weinberg principle?
Because genetic drift occurs much more in small populations
Upsetting the Hardy-Weinberg equilibrium may eventually lead to what?
Evolution
Why are small populations more likely to become extinct?
They tend to have lower genetic diversity and so are worse at responding to change- for example, a pathogen could wipe out an entire population
What is a genetic bottleneck?
When a sudden environmental change drastically reduces the size of the population for at least a generation
What happens to genetic diversity when a genetic bottleneck occurs?
It is greatly reduced for a long period of time
What is a positive effect of a genetic bottleneck?
A beneficial mutation will have a much greater impact and lead to quicker development of a new species
What is the founder effect?
The reduced genetic diversity that results when a population is descended from a small number of colonizing ancestors. The new population can also be very genetically different from the one its founders split off from due to genetic drift and random presence of some alleles in the founders
What is the founder effect an extreme example of?
Genetic drift
What form will the distribution of different variants of characteristics take?
A bell curve (standard distribution)
What happens in stabilising selection?
Average individuals are favoured
What happens in directional selection?
Individuals are favoured in one direction
When does directional selection occur?
When there is a change in the environment and the most common phenotype is no longer the most advantageous, so organisms with more extreme phenotypes are favoured
What happens in disruptive selection?
The extremes are selected for and the average is selected against
What is the opposite of stabilising selection?
Disruptive selection
What is speciation?
The formation of new and distinct species in the course of evolution
What form of speciation is the most common?
Allopatric speciation
What is the sequence of events for speciation?
- Members of a population become isolated and no longer interbreed with the rest of the population, so no gene flow between the groups 2. Random mutation within the groups continues, but each may have different selection pressures 3. Eventually mutations and changes in allele frequency will mean that both populations are so different that they can no longer interbreed and produce fertile offspring
What happens in allopatric speciation?
A population is geographically isolated, and due to different environmental selection pressures speciation occurs
What happens in sympatric speciation?
Speciation occurs despite the two populations sharing the same habitat
What is a reason that sympatric speciation may occur?
Two different species can interbreed and form fertile offspring which has a different chromosome number from either parent species, thus meaning that the new population is genetically isolated
What do prezygotic reproductive barriers do?
Prevent fertilisation and formation of a gamete
What do postzygotic reproductive barriers do?
Reduce the viability or reproductive potential of offspring
What often forms postzygotic reproductive barriers?
Hybridisation
What are 4 examples of problems with artificial selection?
- Makes more docile animals which can’t compete or fight with wild animals 2. Makes more lean animals which could get cold or suffer if food stocks decline 3. Coat colour might not suit environment 4. Inbreeding exacerbates genetic conditions and problems
What is artificial selection?
The selective breeding of plants and animals by humans to produce desirable traits
What are 2 reasons artificial selection reducing genetic diversity is a bad thing?
- More susceptible to genetic diseases 2. Potentially useful alleles for the future are lost
What are 2 problems with artificial selection?
- Can cause health problems by exaggerating certain negative traits 2. Reduces genetic diversity
What is a species?
A population of genetically similar individuals whose members can interbreed and produce fertile offspring
What are 3 types of changes which can cause reproductive isolation, with one example for each?
- Seasonal changes i.e. different mating seasons 2. Mechanical changes i.e. changes in genitalia prevent successful mating 3. Behavioural changes i.e. different courtship rituals developing
What is inbreeding?
Mating between closely related individuals
What is outbreeding?
The breeding of distantly related individuals of a species
How can the problems of inbreeding be mitigated?
Using alleles from gene banks to do outbreeding
What 2 things does outbreeding do?
- Reduced incidence of homozygous recessives 2. Increases the potential to adapt to environmental change
What do seed banks do?
Keep seeds from both wild type and domesticated varieties of plants
What do gene banks do?
Similar to seed banks but keep biological samples other than seeds such as sperm or ova, usually frozen
What are both seed and gene banks?
An important genetic resource
