Isolation And Speciation Flashcards
What is evolution by natural selection
A change in the allelic frequencies within a population
What does it mean if allelic frequency is affected by selection and selection is due to environmental factors
Environmental changes therefore affect the probability of an allele being passed on in a population and hence the number of times it occurs within a gene pool
Environmental factors don’t affect the probability of a mutant allele arising, what do they do
They affect the frequency of a mutant allele that is already present in the gene pool
What is speciation
Evolution of a new species from existing ones
What is a species
A group of individuals that have common ancestry and so share the same genes but different alleles and are capable of breeding with one another to produce fertile offspring
What is adaptive radiation
The different phenotypes each combination of alleles produces will be subject to selection pressure that will lead to each population becoming adapted to its local environment
What does adaptive radiation result in
Changed to the allele frequencies of each population( each population evolves)
What effect does genetic drift have on a smaller population
Genetic diversity is restricted
Small number of different alleles there is not an equal chance of each being passed on
Those passed on quickly affect the whole population as their frequency is high
Any mutation that is favoured will effect the whole population quickly as it’s frequency will be high
Population will change relatively rapidly, making it more likely to develop into a separate species
What will the effect of a mutant allele be like on a larger population
Will be diluted as it’s frequency is far less in the much larger gene pool. The effects of genetic drift are likely to be less, and development into a new species will be lower
What type of population does genetic drift take place in
Small population
What happens during allopatric speciation
Two populations become geographically separated
What may geographical separation be the result of
Any physical barrier between two populations which prevents them interbreeding e.g. oceans, rivers, mountain ranges, deserts
Describe allopatric speciation
Become geographically isolated
So reproductively isolated
The 2 environments may have different selection pressures
So some of the population is more successful in one area then the other
They survive and reproduce, passing in the allele
Over many generations the allele frequency in the population increases
If the 2 populations are put together to interbreed, they will no longer breed to produce fertile offspring - a new species has formed
What’s sympatric speciation
Describes the form of speciation that results within a population in the same area leading to them becoming reproductively separated
Explain how geographical separation of two populations of a species can result in the accumulation of the differences in their gene pools
Geographically isolated populations may experience different environmental conditions. In each is less completion and so the tolerant species’ population becomes larger. Where there is no contamination, all varieties can survive, there is greater competition and so the populations are smaller
What’s the 7 different types of variation
Geographical- physical barriers
Ecological - rarely meet, inhabit different habitats
Temporal - breeding seasons different
Behavioural - courtship
Mechanical - anatomical differences prevent mating occurring
Gametic - may not meet due to genetic incompatibility
Hybrid sterility- can not produce viable gametes
Describe sympatric speciation
Not geographically isolated
But are reproductively isolated
Mutants produced by random mutation may not be able to reproduce with non mutants of a population
In what ways does reproductive isolation occur
Seasonal- individuals from the same population develop different mating seasons, or become sexually active at different types of the year
Mechanical - changes in the genitalia prevent successful mating
Behavioural - a group of individuals develop courtship rituals that aren’t attractive to the main population
