Population and evolution Flashcards
What is a population?
A group of organisms of the same species living in the same space at the same time
What is evolution?
A change in allele frequency in a population
What is a gene pool?
All of the alleles of all of the genes of all of the individuals of a population
What is allelic frequency?
The number of times an allele occurs in the gene pool
What does the Hardy-Weinberg principle calculate?
The frequency of the alleles of a particular gene in a population
What assumptions does the HWP make?
- Large population
- Isolated population
- No selection
- No mutation
- Random mating
What are the two equations used to calculate HWP?
P+q=1 (calculates allele frequency)
P^2 +2Pq+ q^2= 1 (calculates genotype frequency)
What does P + q tell you?
Frequency of dominant and recessive allel
What does P^2 tell yu?
Frequency of homozygous dominant genotypes in the population
What does q^2 tell u?
Frequency of homozygous recessive genotypes in the population
What does 2PQ tell u?
Frequency of heterozygous in the population
What causes variation in phenotype?
Genetic and enviroment factors
Where does genetic variation come from?
- Mutations
- Meiosis
- Random fertilisation of gametes
What are mutation?
Changes to genes and/or chromosomes
Why doe meiosis produces variation?
Meiosis results in new combinations of alleles in the gametes
Why does random fertilisation result in variation
Sexual reproduction results in a new combination of alleles in the offspring. When gametes fuse, introduces further variation
How does the environment play a role in genetic characteristics?
The genes set limits on a characteristics. The environment determines where within the limits the organism lies.
If we record a polygenic characteristic vs number of population, what would the graph shape be?
Bell shaped
What are selection pressures?
Environmental factors which limit the population of a species
Examples of selection pressures
Predation
Disease
Competition
How does selection pressures link to evolution?
Determine the frequency of alleles in a gene pool
What does evolution by natural selection rely on?
Organisms produce more offspring the environment can support.
Their is genetic variety in the population
There are a variety of phenotypes the selection operates against
Why is variation important in natural selection?
Variation within a population allows for the selection pressure to change overtime and for the population to evolve and adapt
What are three types of selection?
Stabilising
Directional
Distruptive
What does stabilising selection favour>
Average
What conditions are conductive for stabilising?
Consistent environment, little chang
What does directional selection favour?
Individuals with phenotypes on one extreme
What conditions are conductive for directional?
A change in the environment which is then consistent
What does disruptive selection favour?
Individuals on both extremes
What conditions favour disruptive selection?
Vary between two distinct parameters favouring both extremes
What is speciation?
Evolution of new species from existing ones
What is a species?
Group of individuals with shared ancestry, share the same genes but different alleles and can breed to produce fertile offspring
What is the most important factor in speciation?
Reproductive isolation followed by genetic change due to natural selection
What are two types of speciation?
Allopatric and sympatric
What is allopatric speciation?
Populations separated by a geographical barrier so no gene flow. Mutations cause variation, different selection pressures causes a change in allele frequency and eventually reproductive separation
Describe sympatric speciation
Separation within a population such as location or time of mating. No gene flow. Mutation causes variation, different selection pressures change the allele frequency until eventually reproductive isolation
What is adaptive radiation?
Process in which organisms diversify from an ancestral species into a multitude of new forms, particularly when exposed to different selection pressures and inhabit different environmental niches
What is genetic drift?
Change in allele frequency through generations due to random chance of alleles being inherited. Also due to genetic mutations.
Describe a population where genetic drift would have a large impact
Small population.
Small change makes big impact as there are only a small number of different alleles.
