7.3 Evolution may lead to speciation Flashcards
Define evolution
Change in allele frequencies in a population
Regarding natural selection, and evolution, what are the primary and secondary causes of variation?
- Mutations primary
- Meiosis secondary
- Random fertilisation of gametes secondary
Effect on gene pools in a smaller population
Smaller populations have smaller gene pools
What does genetic drift cause?
Change in allele frequencies
In what type of populations will genetic drift occur in?
small populations
What phenotypes are best adapted to survive during stabilising selection, and so what happens to phenotypes?
- Intermediate phenotypes best adapted to survive
- As intermediate are advantageous, they become more common, so extreme phenotypes disappear
Example of stabilising selection:
Birth weight in humans
What phenotypes are best adapted to survive during directional selection, and so what happens to phenotypes?
- Extreme phenotypes are best adapted to survive in environment
- As extreme phenotypes are advantageous, they become more common, and intermediate phenotypes disappear
Example of directional selection:
Antibiotic resistance in rats
Describe disruptive selection:
- Population experiences two different selection pressures
- Two phenotypes are advantageous and both become more common
- Speciation occurs
What type of selection results in speciation?
Disruptive
Define allopatric speciation
Formation of new species from different populations, that are reproductivly isolated georgraphically
Describe and explain the process of allopatric speciation
- Two populations become reproductively isolated geographically
- No gene flow between populations
Each population experiences different selection pressures - Variation occurs in each population, due to mutation
- DIfferent alleles are advantageous, so different alleles are passed on
- Change in frequency of alleles
- Disruptive selection
Describe and explain the process of sympatric speciation:
- Two populations become reproductively isolated in the same habitat
- No gene flow between populations
- Each population experiences different selection pressures
- Variation occurs in each population, due to mutation
- Different alleles are advantageous, so different alleles are passed on
- Change in frequency of alleles
- Disruptive selection
- Eventually, populations cannot interbreed to produce fertile offspring
Define sympatric speciation:
Formation of new species from a population that are reproductivly isolated, but not geographically isolated (in the same habitat)
