Population and Evolution Flashcards
Define species
Group of similar organisms that reproduce to give fertile offspring
Define population
Same species living in particular area at same time
Species can exist as 1/more populations
Define gene pool
Complete range of alleles in population
Define allele freq
How often allele occurs in population
What does the Hardy Weinberg principle predict?
Freq of alleles in population won’t change from one generation to next
The Hardy Weinberg prediction only occurs w/in certain conditions.
State the conditions
- Large population
- No : immigration, emigration, mutations, natural selection
- Random mating
What is the Hardy Weinberg equation used for?
- Calculate freq :
- Alleles
- Genotype
- Phenotype
- Test whether principle applies to specific alleles in particular pop - if change then other factor involved
Predicting allele freq. equation
p + q = 1
- p = freq. dominant
- q = feq. recessive
Predicitng genotype and phenotype freq. equation
p2 + 2pq + q2 = 1
- p2 = freq. homo dominant
- q<strong>2</strong> = freq. homo recessive
- 2pq = freq. hetro
What are the causes of genetic variation?
- Mutation
- Meiosis - crossing over + independent segregation
- Random fertilisation
What are most variation w/in species caused by?
Combination of genetic + env factors
Define evolution
Change in allele freq. over time
Give examples of selection pressures
- Predation
- Disease
- Competition
What are the diff. types of natural selection?
- Stabilising selection
- Directional selection
- Disruptive selection
Define stabilising selection
- Env favours individuals w/in the middle range
- Occurs when env isn’t changing
- Reduces range of phenotype
- Mean stays the same
Define directional selection
- Env favours individuals at one extreme
- Response to env change
- Mean changes
Define disruptive selection
- Env favours individuals at either end of extreme - more than 1 phenotype
- Opposite of stabilising bc characteristics towards middle are lost
Define speciation
Development of a new species from existing species
Why does speciation occur?
- Population of same species become reproductively isolated
- No interbreeding
- Genetic variation occurs w/in population due to mutations
- Diff. selective pressures
- Best adapted survive + reproduce, passing it onto offspring
- Change in allele freq.
- Can no longer interbreed to produce fertile offspring
What are the types of speciation
- Allopatric speciation
- Sympatric speciation
Outline what happens during allopatric speciation
- Geographical isolation - experience diff. conditions
- Physical barriers prevent interbreeding
Outline sympatric speciation
- Occurs in same env - doesn’t require geographical isolation
- Mutation prevents interbreeding
- Become reproductively isolated
Outline ways reproductive isolation occurs
- Seasonal - develop diff. flowering/mating seasons, or become sexually active at diff. times of year
- Mechanical - changes in genitalia prevent successful mating
- Behavioural - develop courtship ritual that aren’t attractive to main population
Define genetic drift
When chance, rather than env factors, dictates which individuals survive, breed + pass on their alleles
When does evolution by genetic drift usually have a greater effect?
Small population - chance has greater influence
What might cause changes in allele freq?
- Natural selection
- Mutations
- Genetic drift
Which factors are involved in evolution?
- Natural selection
- Genetic drift
- BUT one can drive evolution more than other depending on population size
