Populations and evolution Flashcards
Gene pool definition
Total information from all the genes and alleles of the breeding individuals in a population at a particular time
Allele frequency definition
The number of that allele divided by the total number of alleles for that gene in a population
Hardy Weinberg principle
The proportion of dominant and recessive alleles in a population remains constant from one generation to the next.
What are the 5 conditions needed for the hardy Weinberg principle to be met
- no mutations
- isolated population
- no selection
- large population
- random mating in the population
Is p the frequency of the dominant or recessive allele
Dominant
Is q the frequency of the dominant or recessive allele
Recessive
What is the first equation for hardy Weinberg
P + Q = 1
What is the hardy Weinberg formula
P2 + 2pq + Q2 =1
Psquared is the frequency of homdom
2pq is frequency of hetero
Q2 is frequency if homrec
Strategy for working out hardy Weinberg
1) work out the hardy Weinberg frequency
2) turn this into a probability
3) usually need to calculate p and q
4) work out hardy Weinberg frequency you need to work out
5) calculate it (probability)
6) check by adding up to 1
7) multiply to make units needed in the answer I.e %
What are the ways to get variation
Environment
Mutation-new alleles
Meiosis -crossing over(new combinations)
Meiosis-independent segregation
Meiosis-random assortment of sister chromatids
Any sperm can fuse with any egg - random fertilisation
Discontinuous variation
- bar charts
- limited number of traits, no intermediate forms
- controlled by few genes(usually multiple alleles)
- environment has little effect on these characteristics
- eg blood group
Continuous variation
- histograms
- range of gradation of characteristics
- controlled by many genes (polygenic)
- environment has significant effect
- eg height
Selection pressures definition
Environmental factors that limit the population of a species e.g. predation, disease and competition
Species definition
Group of organisms that can interbreed successfully to produce fertile offspring
Limitations of the species concept
Doesn’t apply to all
Can’t tell if extinct animals can/can’t breed
Natural selection process
Apply to Q
1) variation occurs in a species
2) due to mutation
3) selection pressure causes some organisms to be disadvantaged
4) some organisms are better adapted(phenotype)-anitomical, physiological or behaviours
5) these survive and reproduce(differential reproductive success
6) increasing the frequency of their successful alleles in the next generation
Evolution means natural selection depends on
Over production - produce more than can support with supply of food light space etc
Genetic variety in populations of all species
Variety of phenotypes that selection operates against
Role of overproduction
Ensure enough organisms survive to reproduce in next generation
Alternative is lower rate but good parenting to ensure young survive
What is the selection pressure for over producing species
Intra specific competition
Role of variation in natural selection
Is essential when there are changing selection pressures so natural selection can occur
Stabilising selection
- mean stays the same
- standard deviation occurs
- reduces variation
- occurs in an unchanging environment
Graph gets thinner >
Directional selection
- mean changes
- standard deviation not altered much
- phenotype at end of a range is selected for
- environment changing
Graph moves to either side but is same shape
> or
Disruptive selection
- opposite of stabilising
- selection pressure toward extremes, creates 2 moral values
- over time when species evolve 2 means and 2 standard deviation form —— 2 different species
Graph has two bumps <>
What is evolution
A change in allele frequencies in a population
What is speciation
Evolution of a new species from existing ones
What is reproductive isolation
Members are reproductively separated from others (can’t breed)
Is the most important way new species are formed. Followed by genetic change
What is adaptive radiation
Changes in different populations to local selection pressures
Genetic drift
Occurs most in small isolated populations
Genetic diversity is less because there is a smaller gene pool
Any favourable mutation will spread more quickly through this population
Population will change more quickly and is more likely to develop into a new species
What is allopatric speciation
The formation of a new species when there has been geographical isolation
A geographical barrier for one organism might not be for another
What are the 7 steps in allopatric speciation
1) organisms of Same prices are separated into 2 groups b physical barrier so can’t interbreed
2) prevents gene flow between the 2 groups’ gene pools
3) variation exists in each population due to mutations occurring in each population
4) if there are different selection pressures on the 2 groups it will cause different phenotypes to be selected in natural selection
5) 2 groups evolve differently (as have different alleles)
6) in time differences between 2 gene pools are so great that they are now separate species
7) the 2 species groups will not be able to interbreed to produce fertile offspring as they are now different species
What is sympatric speciation
Speciation where the organisms are living in the same area( not geographically isolated) but reproductive isolation occurs
What are the methods of sympatric speciation
- geographical > isolated by physical barriers
- ecological > different habitats in same area
- temporal > different breeding seasons
- behavioural > different courtship
- mechanical > anatomical differences
- gametic > gametes can’t meet due to genetic/biochemical incompatibility
