Module 7- Evolution 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
How has evolutionary change resulted in greater diversity?
Evolution is a result of speciation and natural selection
3 marks
In South America, there are several species of guinea pig. They are thought to have arisen by sympatric speciation.
Explain how sympatric speciation may have occurred.
- Mutation occurs
- Temporal: different breeding seasons
- Differenct selection pressure–> change in allele frequency
Define population
Group of organisms of the same species
Occupying a particular space, at a particular time, that can potentially interbreed
6 marks
On islands in the Caribbean, there are almost 150 species of lizards belonging to the genus Anolis. Scientists believe that these species evolved from two species found on mainland USA. Explain how the Caribbean species could have evolved.
- Geographical isolation
- Separates gene pools
- Variation due to mutation
- Different selection pressures
- Different reproduction success- selected organisms survive and reproduce
- Increase in allele frequency
5 marks
Changes in ecosystems can lead to speciation. In Southern California 10 000 years ago a number of interconnecting lakes contained a single species of pupfish.
Increasing temperatures caused evaporation and the formation of separate, smaller lakes and streams. This led to the formation of a number of different species of pupfish. Explain how these different species evolved.
- Geographical isolation
- Variation due to mutation
- Different environmental conditions / selection pressures
- Organisms with beneficial allele survive and reproduce
- Leads to change in allele frequency
1 mark
Define gene pool
All the alleles in a population
1 mark
Define allele frequency
The proportion of each allele in a gene pool
5 marks
Variation in flower colour is considered one of the factors involved in the evolution of the following two species of monkeyflower.
* Erythranthe lewisii (Great Purple Monkeyflower), which has pink flowers, is mostly found at higher altitudes (1600 to 3000 metres) and attracts bumblebees.
* Erythranthe cardinalis (Scarlet Monkeyflower), which has red flowers, is mostly found at lower altitudes (up to 2000 metres) and attracts hummingbirds.
Bumblebees and hummingbirds are important in the pollination of flowers. Pollination involves the transfer of male gametes to female gametes. Explain the different processes that may have been involved in the evolution of these two species of monkeyflower. Use the information provided to justify your answer.
- Geographical isolation/separation due to altitude
- Allopatric speciation due to isolation
- Different selection pressures
- However some overlap in distribution
- So sympatric speciation
- Variation due to mutations
- Separate gene pools due to different altitudes
- Different allele frequency in each population
- Different species can no longer interbreed to produce fertile offspring
1 marks
The scientists used the mark-release-recapture method to determine the number of lemurs in one area of forest. They captured, marked and released a first sample of 30 lemurs. A week later, they captured a second sample of 25 lemurs from the same area of forest. The scientists calculated that there were 250 lemurs in that area of forest. Suggest one precaution needed when marking the lemurs to make sure the estimate of the number of lemurs is valid.
Marking does not affect survival/predation/recapture
