7B - Speciation and genetic drift Flashcards
What is speciation?
The development of a new species from an existing species.
When does speciation occur?
When populations of the same species become reproductively isolated - changes in allele frequency cause changes in phenotype, which mean they can no longer interbreed to produce fertile offspring.
What when populations of a species become isolated, does changes in the allele frequency cause?
Changes in phenotype, which mean they can no longer interbreed to produce fertile offspring.
When can reproductive isolation happen?
When a physical barrier, e.g. a flood or an earthquake, divides a population of a species, causing some individuals to become separated from the main population. This is known as geographical isolation and leads to allopatric speciation.
Alternatively, speciation can also occur when a population becomes reproductively isolated without any physical separation. This is known as sympatric speciation.
What does geographical isolation lead to?
Allopatric speciation.
What is geographical isolation/allopatric speciation?
When a physical barrier, e.g. a flood or an earthquake, divides a population of a species, causing some individuals to become separated from the main population. This is known as geographical isolation and leads to allopatric speciation.
What is sympatric speciation?
Occurs when a population becomes reproductively isolated without any physical separation. This is known as sympatric speciation.
What does allopatric speciation require?
Geographical isolation.
Describe the process of allopatric speciation
1) Populations that are geographically separated will experience slightly different conditions, e.g. a different climate.
2) This means the populations will experience different selection pressures and so different changes in allele frequency could occur.
3) The changes in allele frequency will lead to differences accumulating in the gene pools of the separated populations, causing changes in phenotype frequencies.
4) Eventually, individuals from the different populations will have changed so much that they won’t be able to breed with one another to produce fertile offspring - they’ll have become reproductively isolated.
5) The two groups will have become separate species.
What differences in allele frequencies could occur in allopatric speciation as a result of the different populations experiencing different selection pressures?
- Different alleles will be more advantageous in the different populations. For example, if geographical separation places one population in a colder climate than before, longer fur length will be beneficial. Directional selection will then act on the alleles for fur length in this population, increasing the frequency of the allele for longer fur length.
- Allele frequencies will also change as mutations occur independently in each population.
- Genetic drift may also affect the allele frequencies in one or both populations.
How does a species separate as a result of geographical isolation?
- There starts of as one population of individuals.
- Then physical barriers stop interbreeding between populations.
- Populations adapt to new environments.
- Allele and phenotype frequency change, leading to development of new species.
What causes reproductive isolation in sympatric speciation?
Random mutations within a population, preventing members of that population breeding with other members of the species.
What types of changes can cause reproductive isolation?
Seasonal, mechanical and behavioural.
How can seasonal changes cause reproductive isolation?
Individuals from the same population develop different flowering or mating seasons, or become sexually active at different times of the year.
How can mechanical changes cause reproductive isolation?
Changes in genitalia prevent successful mating.
