7.3 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
Describe disruptive selection
- Population experiances two different selection pressures
- Two phenotypes are advantageous and both become more common
- Speciation occurs
Graph for disruptive selection
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 reproductivly isolated geographically
- No gene flow between populations
- Each population experiances different selection pressures
- Variation occurs in each population, due to mutation
- DIfferent alleles are advanatageous, so different alleles are passed on
- Change in frequency of alleles
- Disruptive selection
- Eventually, populations **cannot interbreed to produce fertile offspring **
Describe and explain the process of sympatric speciation
- Two populations become reproductivly isolated in the same habitat
- No gene flow between populations
- Each population experiances different selection pressures
- Variation occurs in each population, due to mutation
- DIfferent alleles are advanatageous, 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)
Explain stabilising selection
- Mean/intermediate phenotypes best adapted to survivie in unchanging enviroment
- Selection against extreme phenotypes in favour of mean/intermediate phenotypes
- Range and standard deviation reduced
Example of stabilising selection
Birth weight in humans
Explain directional selection and give an example
- Extreme phenotype is best adapted to survive in unchanging enviroment
- Selection against mean/intermediate phenotypes in favour of extreme phenotypes
- Range and standard deviation reduced
Example of directional selection
Antibiotic resistance in rats
