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
What types of populations does genetic drift have the largest effect on and why
Small populations
Small number of individuals obtain large proportion of alleles
Define the bottle neck effect
A sharp decrease in population size causing a random set of alleles to survive
Define founder effect
Population decends from a small number of colonizing ancestors
Low genetic diversity
Define allopatric speciation
Populations are geographically isolated
Describe how speciation occurs
Population becomes reproductive isolated so no gene flow
Different selection pressures are present in each population due to different abiotic and biotic factors
Genetic variation in each pop due to mutations.
Genetic drift causes random changes to allele frequency
Different alleles are. Advantageous in each population
Different phenotype selected for
Advantageous alleles make organisms more likely to survive and reproduce
Frequency of advantageous allele increases at the expense of less advantageous alleles.
Gene pools diverge so much no longer able to produce fertile offspring
Adaptive radiation
Define sympatric speciation
In same area but still reproductive isolated
Types of isolation
Geographical Ecological Temporal Behaviuoral Mechnaical Gametic Hybrid sterility
Define ecological isolation.
Same areas but different habitats or niches
Define temporal isolation
Breeding seasons don’t align
Define behavioural isolation
Different courtship behaviours
Define mechanincal isolation
Anatomical differences
Define Gametic isolation
Genetic or biochemical incompatibility preventing gamete fertilisation
Define hybrid sterility
Hybrids can’t produce viable offspring
