20. Natural selection and speciation Flashcards
What is natural selection
the process that leads to evolution
What is evelution
the change in the frequency of alleles within a population over many generations.
What causes changes to allel frequencioes
differential reproductive success – some phenotypes are more likely to survive and reproduce than others
What are the causes of variation in any population
· mutations
· meiosis
· Random fusion of gametes
What results in selection pressures
Predation, disease, competition and changes in the environment
giving some phenotypes a selective advantage acting as a trigger for natural selection to occur.
What is the process of natural selection
· There is variation in a population.
· is due to random mutations giving rise to new alleles of a gene.
· Organisms that have advantageous alleles, will have a phenotype that give them a selective advantage
· Organisms with advantageous alleles are more likely to survive to reproduce
· These organisms are more likely to pass on advantageous alleles to the next generation
· causes an increase in the frequency of the advantageous allele in that population over many generations.
What is an example of anotomical adaptations
Changes to the organisms body, such as beak shape
What is an example of physiological adaptations
Haemoglobin with a different oxygen affinity
What is an example of behavioural adaptations
Better food search strategies / more elaborate songs in whales
What are the different types of selection
- Directional.
- Stabilising .
- Disruptive.
What is directional selection
Occurs when the environment changes
acts against one of the extreme phenotypes and selects the other. This results in an increase in the frequency of alleles resulting in the most successful phenotype.
What is stabilising selection
occurs in an unchanging environment
type of selection acts against both the extremes in a range of phenotype. Acts to prevent change
What is disruptive selection
occurs in a fluctuating environment
individuals with both extremes of a phenotype have a selective advantage over those in the middle, so both are selected. The intermediate phenotypes are selected against.
What is a species
A group of organisms with similar characteristics that can interbreed to produce fertile offspring
What is speciation
Speciation is a process whereby one gene pool gives rise to more than one gene pool.
What are the types of speciation
Allopatric speciation
Sympatric speciation
What is allopatric speciation
occurs when two populations of the same species become geographically separated by a physical barrier
prevent the separated populations from interbreeding.
What happens to genetic differences in allopartic speciation
genetic differences between the populations increase through selection due to the different environmental conditions so different selection pressures. Eventually, the two populations are unable to interbreed and have become distinct species
What is sympatric speciation
the two populations may inhabit the same area, but still evolve into 2 different species
occur due to random mutations leading to differences that prevent individuals with the mutation from breeding with other members of the population that do not carry the mutation. This is called reproductive isolation
What are causes of sympatric speciation
Seasonal / temporal isolation
Mechanical isolation
Behavioural isolation
How does sesonal isolation cause sympatric speciation
members of the two populations reproduce at different times of the year
How does mechanical isolation cause sympatric speciation
anatomical differences may prevent mating occurring
How does behavioural isolation cause sympatric speciation
For example - members of the two populations have different courtship patterns
How does evolution occur via genetic drift
chance rather than environmental factors dictate which alleles are passed on. Genetic drift can lead to differences in allele frequencies between two isolated populations. Over time, this could lead to reproductive isolation and speciation
The smaller a population the bigger the impact these chance changes in allele frequency will have – hence evolution often occurs more rapidly in smaller populations.
