Evolution Flashcards
How does variation in a species happen
Mutations
Alleles
Crossing over and independent segregation
Environmental- climate, food, lifestyle
Define evolution
The frequency of an allele in a population changes over time
Explain evolution by natural selection
Individuals vary due to different alleles
Selection pressures create a struggle for survival
Individual with beneficial alleles not the selection pressure are more likely to survive and reproduce
Passing on the successful genes
A greater proportion of the next gen will have the beneficial alleles
And are more likely to survive and reproduce
Increasing the allele frequency in the gene pools
What is stabilising selection
Alleles for a phenotype in the middle ground are favoured so are more likely to survive and reproduce
Where does stabilising selection occur
The environment isn’t changing and reduces the range of phenotypes
What is directional selection
Individuals with alleles for an extreme phenotype are more likely to survive and reproduce
Why does directional selection happen
Environmental change
What is disruptive selection
Individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce
When does disruptive selection happen
The environment favours more than one phenotype
What is assortative breeding
Non random
Leads to 2 different breeding populations
What is speciation
The development of a new species from an existing species
Describe speciation
Populations of the same species become reproductively isolated
Causing changes in allele frequency
Changing the phenotype
The 2 populations can no longer interbreed to produce fertile offspring
What is allopatric speciation
Populations separated by a physical barrier
So the populations are geographically isolated
And experience slightly different environmental conditions
So experience different selection pressures
And different phenotypes are beneficial
So change allele frequency and phenotype frequency
Until the 2 populations are so different they are reproductively isolated
Why does allele frequency change
Different alleles are advantageous for different populations in different environments.
Mutations
Genetic drift
What is sympatric speciation
Populations don’t have to be geographically isolated
Members of the population have random mutations preventing them breeding and becoming reproductively isolated
How is polyploidy an example or sympatric speciation
Most eurkaryptic orgs have a diploid number of chromosomes
Mutations create polyploid organisms
That can’t reproduce sexually to give fertile offspring
So are reproductively isolated
If the polyploid org reproduces asexually to give fertile offspring a new species will be created
When can speciation only occur
If the change isn’t fatal
When does reproductive isolation occur
When changes in alleles ans phenotypes prevent orgs reproducing successfully
What is an example of Seasonal reproductive isolation
Individuals of the same species develop different mating/flowering seasons
What is an example of mechanical reproductive isolation
Changes to genitalia
Give an example of behavioural reproductive isolation
Individuals of the same species develop different courtship rituals that aren’t attractive to the main populations
Explain genetic drift
Individuals in a population show genotype variation
By chance the allele for 1 genotype is passed on more than the other
So the allele frequency of that genotype increases
Changes in allele frequency in 2 isolated populations could lead to reproductive isolation and speciation
When does genetic drift have a bigger impact
In smaller populations because chance has a greater influence
As large populations chance variations even out
