Key Area 7 Flashcards
What is natural selection
This is the non-random increase in frequency of DNA sequences that increase survival and the non-random reduction in the frequency of deleterious sequences.
What are the 3 types of natural selection
Stabilising
Directional
Disruptive
How does stabilising selection occur
Stabilising selection occurs when the average phenotype is selected for and extremes of the phenotype range are selected against.
When natural selection has a stabilising effect, the mean phenotype remains unchanged but the range of
phenotypes is narrower
How does directional selection occur
Directional selection occurs when one extreme of the phenotype range is selected for
When natural selection has a directional effect, the mean phenotype and range of phenotypes change
How does disruptive selection occur
Disruptive selection occurs when 2 or more phenotypes are selected for.
When natural selection has a disruptive effect, 2 new mean phenotypes result and the range of phenotypes is altered.
Why is natural selection in prokaryotes more rapid
Prokaryotes can exchange genetic material (genes) horizontally, resulting in faster evolu- tionary change than organisms that only use vertical gene transfer ( from parent to off- spring/one generation to the next)
What is horizontal gene transfer
Horizontal gene transfer is where genes are transferred between individuals in the same generation.
What is vertical gene transfer
Vertical Gene Transfer is where genes are transferred from parent to offspring (different generation) as a result of sexual or asexual reproduction.
What is a species
A species is a group of organisms capable of interbreeding and producing fertile offspring, and which does not normally breed with other groups.
Speciation is the generation of new biological species by evolution as a result of:
Isolation
Mutation
Selection
What speciation do geographical barriers lead to
Allopatric
Speciation.
What do Behavioural or Ecological barriers lead to
Sympatric Speciation.
What is Sympatric Speciation.
In Sympatric speciation the behavioural or ecological barriers prevent gene flow between populations living side by side but do not interbreed and so natural selection is able to act separately on the 2 sub-populations.
