3. Speciation And Genetic Drift Flashcards
What drives evolution ?
Natural selection
Allowed species to change over time and new species to evolve
What is speciation ?
Development of new species from an existing species
Occurring when populations of same species become reproductively isolated - can’t interbreed because changes in allele frequency cause changes in phentotyoe
How can reproductive isolation occur ?
Physical barrier eg flood which divides the population of species causing individual to become separated from main population - GEOGRAPHIC ISOLATION
There is no gene flow between 2 populations which can lead to allopathic speciation
Or when population become reproductively isolated without any physical barrier - sympathetic speciation
What happens to populations that are geography separated ?
Different conditions - climate
So different selection pressure and different allele frequencies could occur
Separated populations
Different alleles will be more advantageous
So different alleles will be more advantageous in different populations so natural section occurs
Eg colder climate directional section will take place as fur length increase becuase those with long fur can survive / reproduce and pass on their alleles. Those with average / short fur decrease in pop size
What else will occur in separated populations ?
•Mutations which change allele frequency
Advantageous or harmful so will either just die out or frequency will increase
•genetic drift
So if the organisms are isolated geographically for a long period of time ; what will happen C
Speciation will occur
Changes in allele frequency will lead to differences accumulating in gene pools causing changes in phenotype frequencies
Eventually won’t be able to breed and produce fertile offspring - reproductively isolated as now separate species
What is sympatric speciation ?
Occur when random mutations within a population prevent individuals that carry the mutation from breeding with other member of population that don’t carry it
NO GEOG ISOLATION
How common is sympatric speciation
Rare
Difficult for a section of population to become completely reproductively isolated from rest of population without being geographically isolated too
How does reproductive isolation occur ?
Changes in alleles
Genotypes
Phenotypes which prevent. Individuals with changes from successfully breeding
What it’s important to note about geographical isolation ?
They are separately isolated
They may still be able to successfully breed if bought back togther
It CAN LEAD to reproductive isolation if natural selection occurs and changes the allele frequcies
What 3 changes occur due to reproductive isolation ?
- seasonal changes - develop flowering/mating seasons or become sexually active at different times of year. So can’t breed together as they aren’t reproductively active at same time.
- mechanical changes - changes in size/ shape / function of genitalia prevents mating
- behavioural changes - courtship rituals which don’t attract to rest of species like dancing / singing - stops breeding
What 2 things can cause evolution ?
Natural selection
Genetic drift
How does evolution work by genetic drift ?
- individuals within population show variation in genotypes ( A and B )
- by change the allele for one genotype ( B ) is passed on to more offspring than the others. So number of individuals with this allele increases
- by chance the same allele is passed on more often again and again - lead to evolution as allele frequency increases in pop
What else is genetic drift called ?
Random drift
What 4 things could genetic drift lead to ?
Evolution
( because of ) changes in allele frequency
( which could lead to ) reproductive isolation and speciation
What is difference between genetic drift and natural selection V
Genetic drift is due to chance
Natural selection is when characteristic become more common as they increase chances of survival
Genetic drift and population size
Evolution by genetic drift usually has greater effect in smaller populations where chance has a greater influence
In larger populations any chance factors even out across whole pop
Genetic drift and diversity
Decrease in genetic diversity
Meaning species less adaptable to future changes in environmental so could be fatal
Evolution of human blood groups
Blackfoot Indiana = A
Navajos = O
Blood group doesn’t affect survival or reproductive success so speciation hasn’t occurred and it’s not due to evolution but natural section.
Caused by evolution due to genetic drift as blood group O was passed on more often in Navajo tribe so over time more common
Why wouldn’t hardy wineberg apply to populations affected by genetic drift?
As populations affected by genetic drift tend to be smaller
HW looks at larger populations
What is diversity of life on Earth today due to ?
Speculation and evolutionary change over millions of years
Only one pop or organism
The pop was divided and new pop evolved into separate species
New species divided and new pop evolved into separate species
This process repeated over long period of time
