Module 7 - Evolution may lead to speciation Flashcards
What is genetic variation?
This is when there is a variation of alleles in a species
What are the 3 main sources of genetic variation?
- Mutations
- Crossing over and independent segregation
- Random fertilisation
What is evolution?
This is when a frequency of an allele in a population changes overtime.
What is the main method to allow evolution to occur?
Natural selection
What are the 3 types of natural selection?
- Stabilising selection
- Directional selection
- Disruptive selection
What is the difference between stabilising and directional selection?
Stabilising is when alleles move towards the middle of the range whereas directional is when Individuals with alleles for an extreme phenotype are more likely to survive and reproduce
What is disruptive selection?
This is when alleles for an extreme phenotype at either end of the ranges are more likely going to survive
Explain how disruptive selection works within birds
In a species, two organisms have different alleles which give them a different characteristic. For example, a bird with a small beak and a bird with a long beak. The bird with a small beak can pick up small seeds and a large beak can pick up large seeds. A bird with a medium beak has no benefit. Therefore his creates a selection pressure with the small and larger beak birds and they are more likely to survive, reproduce and pass on the advantageous allele
What is speciation?
This is the development of a new species from an existing species.
How does speciation happen?
It happens when a species becomes reproductively isolated which causes a change in allele frequency which can cause changes in phenotypes?
What are the 2 different types of speciation?
Allopatric speciation and sympatric speciation
What is allopatric speciation?
This is speciation which requires geographical isolation. It happens when a population is geographically separated causing both populations to experience different selection pressures. The ones that are best adapted will be able to survive and reproduce and pass on their advantageous alleles. Eventually both populations will have changed so much that they cannot reproduce to produce fertile offspring
What is sympatric speciation?
This is speciation which doesn’t required geographical isolation. This occurs usually when mutations occur in the population meaning members of the same species can no longer breed to produce fertile offspring. If the organism that is reproductively isolated reproduces asexually, it could create a new species
What is genetic drift?
This is when chance rather an environmental factors influence whether individuals survive, breed and pass on their alleles. For example if an allele is passed on more often than another by chance, this can eventually lead to reproductive isolation
How is genetic drift more significant in smaller populations than larger ones?
In smaller populations, there is a greater chance of an allele being passed on more often than another
