Population And Evolution Flashcards
Population
A group of organisms of the same species that live in the same area, at a particular time and can interbreed
Gene pool
All the alleles of all the genes of all the individuals in a population at a given time
Allelic frequency
The number of times an allele occurs within the gene pool
Hardy - Weinberg principle
Calculates the frequency of alleles of a particular gene in a population
Assumes- proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to the next
Why Hardy Weinberg might not apply
Mutations Population is not isolated There maybe selection - only some alleles passed Population is small Mating within population is not random
Hard Weinberg equation
P (dominant)
q (recessive)
P+q = 1
P2 + 2pq + q2 = 1
Causes of genetic variation
Mutations
Meiosis - different alleles passes
Random fertilisation of gametes- new combination of alleles for offspring
What kind of variation is genetic variation
Discontinuous variation
Controlled by a single gene
Organisms fit into a few distinct forms
ABO blood group - variation controlled by single gene
bar chart can be produced
Environmental factors that influence the way organisms genes are expressed - variation
Climatic change (e.g. Temperature, rainfall, sunlight)
Soil conditions
PH
Food availability
What kind of data is continuum
Continuous data
A continuum - e.g mass and height
Controlled by poly genes
Bell shaped curve called normal distribution curve can be drawn
Selection pressures
Environment that limit the population of a species
Determine the frequency of alleles
Types of selection pressures
Predation
Disease
Competition
How does evolution occur
By natural selection
For natural selection to occur what factors are needed
Organisms to produce more offspring than can be supported
Genetic variety within the population of all species
A variety of phenotypes that selection operates against
Why is Over production of offspring in natural selection needed
So that a large population survives to breed and produce next generation
Compensates for high death rates (from disease, natural disasters, extreme temp, competition for food)
Natural selection
Some organisms are better adapted for survival in their given habitat
Individuals best suited to environment more likely to survive
Individuals are more likely to breed and pass on favourable allele to next generation
Frequency of this allele in the gene pool will increase
Why is there variation in natural selection
Conditions change overtime and having a range of genetically different in the population - some will have the genes needed to survive in any circumstance
Populations showing little variation - more vulnerable to disease etc
Stabilising selection
Preserves the average phenotype of a population
Selection against the the extreme phenotypes
Directional selection
Changes the phenotypes of a population by favouring phenotypes that vary in one direction from the mean of the population
Selection for one extreme phenotype
Disruptive selection
Favours individuals with extreme phenotypes rather than those with phenotypes around the mean of the population
Speciation
The evolution of new species from existing ones
How new species are formed
Reproductive separation
Speciation lead to different species to evolve
- Geographical isolation
- Variation due to mutation
- Different environmental conditions - causes selection pressure
- Selection for different favourable allele
- Organism survive and reproduce
- Leads to change in allele frequency
- Each population unable to interbreed/ each population becomes different species/ each with own gene pool
Genetic drift in small populations
- Genetic diversity is less
- Allele passes or mutations - quickly Affects the population because frequency is high
- Population will change rapidly + more likely to develop into separate species