Populations And Evolution Flashcards
Define allelic frequency
Frequency of an allele
Define gene pool
All alleles in a population
What conditions must be met in the Hardy weinberg principle
No mutations Large population Isolated population No selection pressure Mating is random
How is phenotype arranged when variation is mainly due to genotype
Distinct groups
Bar chart
How is phenotype arranged when variation is mainly due to environment
Continuum
Normal Distribution
What are the causes of genetic variation
Meiosis
Mutation
Random fertilisation
Define selection pressure
Environmental factor limiting population
What factors drive natural selection
Overproduction of offspring Genetic variation Phenotypic variation Selection pressure Intraspecific competition for resources
Describe how natural selection occurs
More offspring than is needed is produced.
Gene pool contains a variety of alleles
Mutations cause new alleles to arise
Organisms with advantageous alleles more likely to obtain resources, survive and reproduce
Advantageois alleles passed down generations due to selective advantage
Freq of new allele increases at expense of less advantageous ones.
Define evolution
Change in allele frequency
Why do population sizes remain constant despite over production of offspring
Intraspecific competition
Types of selection.
Disruptive, directional and Stabalising
When does directional selection occur
Chnage to environment that is constant and in one direction
What changes are made by directional selection
Change to phenotype same variation
Describe how antibiotic resistance occurs in bacteria
New allele produced via mutation coding for enzyme comp to antibiotic causing antibiotic breakdown so organism is resistant.
Upon exposure to antibiotics organisms with new allele are more likely to survive and reproduce (binary fission).
New allele passed on down generation’s via plasmids. Increase in allelic frequency
When does stabilising selection occur
When there is no chnage to the environment
What effects does Stabalising selection have
Less variation
Same phenotype
When does disruptive selection occur
When there is a fluctuation in an environment
What occurs due to disruptive selection
Two extremes are favoured at the expense of the intermediate forms
New species
What type of selection drives evolution
Disruptive
Define speciation
Formation of new species
Define genetic drift
Change to allele frequency due to chance events
Give examples of events causing genetic drift
Lightning
Earthquake
What two subcategories of genetic drift are there
Bottle neck
Founder effect
