Evolution Flashcards
What is evolution?
The change in organisms over generations as a result of genomic variations.
What is natural selection?
The non-random increase in frequency of DNA sequences that increases survival and the non-random reduction in frequency of deleterious (harmful) sequences.
What are the three types of selection?
- stabilising
- directional
- disruptive
What is stabilising selection?
The average phenotype is selected for whilst the extremes on either side are selected against.
What is directional selection?
One extreme of the phenotype range is selected for as it gives a selective advantage.
What is disruptive selection?
Two or more phenotypes are selected for on either side of the average.
What is the effect of stabilising selection?
There is a smaller range of values so less variation as having the average phenotype gives the organism an advantage.
What is the effect of directional selection?
There is still a range of values but the average has changed as the advantageous trait that was rare is now more common.
What is the effect of disruptive selection?
The population is split into two or more distinct groups with different characteristics (not speciation).
What are the two methods of gene transfer?
- vertical
- horizontal
What is vertical gene transfer?
Genes are transferred from parent to offspring due to sexual or asexual reproduction - called inheritance.
What is horizontal gene transfer?
Genes are transferred between individuals in the same generation.
What type of cell does vertical gene transfer occur in?
Eukaryotes and prokaryotes.
What type of cell does horizontal gene transfer occur in?
Prokaryotes.
What impact does horizontal gene transfer have on the population?
Faster evolutionary change.
What is speciation?
The generation of new biological species by evolution.
What are three ways speciation can occur?
- isolation
- mutation
- natural selection
What is an isolation barrier?
It splits a population into sub-population allowing mutations to take place in both sub-groups, then natural selection takes place, then speciation.
What do isolation barriers prevent?
Gene flow between the sub-populations.
What are the three types of isolation barriers?
- geographical
- behavioural
- ecological
What is a geographical barrier?
Separates a population by natural features like a mountain or river - resulting in allopatric speciation.
What do geographical barriers result in?
Allopatric speciation.
What is a behavioural barrier?
Two populations capable of interbreeding that don’t due to differences in reproductive strategies - sympatric speciation.
What do behavioural barriers result in?
Sympatric speciation.
What is an ecological barrier?
Separation by an ecological niche such as pH levels, salinity, or breeding locations differing between populations - sympatric speciation.
What do ecological barriers result in?
Sympatric speciation.
What is allopatric speciation?
Populations become isolated due to geographical barriers physically separating them.
What is sympatric speciation?
Populations live in close proximity in the same environment yet become isolated due to behavioural or ecological barriers.
