Evolution 1.7 Flashcards
Evolution definition
The gradual change in species over generations, resulting in genomic variation.
What is evolution caused by
Natural selection
Why does evolution occur
To allow a species to become better adapted to their environment.
Natural selection definition
The non random increase in occurrence of advantageous sequences of DNA which would increase the chance of survival and reproducing, and a non random decrease in the occurrence of deleterious DNA sequences, which are the DNA sequences that would cause harm in an organism.
Selection pressures definition
The factors resulting in natural selection.
Selection pressure examples
Increased competition
Changes in environment
Introduction of new diseases
Introduction of new predators
Types of natural selection
Stabilising
Directional
Disruptive
Stabilising natural selection definition
Where organisms with phenotypes at both extremes are not favoured and removed from the gene pool and the more common phenotype is favoured and remains in the gene pool
Directional selection
Where organisms with phenotypes of one extreme is favoured and remain in the gene pool, with the other phenotypes being removed from the gene pool
Directional selection results
Results in mean phenotype will shift left or right (towards an extreme)and the variation decreases.
Stabilising selection result
the mean phenotype stays the same but the variation decreases .
Disruptive selection
Where those with phenotypes at both extremes are favoured and remain in the gene pool, but the common phenotype is removed due to not being favoured.
Result of disruptive selection
There are now two new and separate mean phenotypes and variation decreases.
Phenotype definition
The physical traits that an organism expresses.
Gene transfer two methods
Horizontal and vertical
Horizontal gene transfer definition
Where genes are passed between different individuals of the same generation.
Horizontal gene transfer occurs in
Prokaryotes
What type of gene transfer is the fastest
Horizontal gene transfer
What type of gene transfer is the slowest
Vertical gene transfer
Vertical gene transfer definition
Where genes are passed between organisms of different generations in sexual or asexual reproduction.
Where does vertical gene transfer occur
In eukaryotes
Vertical gene transfer in sexual organisms
Parents will reproduce with each other, the offspring receive one set of chromosomes from each parent, which increases variation.
Vertical gene transfer in asexual organisms
Where parent organisms reproduce on their own producing genetically identical organisms and decreasing variation.
Species definition
A group of organisms which can interbreed to reproduce fertile offspring.
Speciation definition
The process where a new species is formed through evolution, involving isolation, mutation, adaptation and natural selection, and these organisms no longer being able to reproduce with each other.
Types of isolation barriers
Geographical
Behavioural
Ecological
Geographical isolation barriers
An isolation barrier which splits up a population, by stopping organisms interbreeding with each other, through physical landmarks.
Ecological isolation barriers
Isolation barriers where a population is split up, stopping organisms from interbreeding, through change in abiotic factors
Behavioural isolation barriers
An isolation barrier which splits up a population, stopping them from interbreeding with each other, through differences in how the organisms act.
Stages of speciation
Isolation
mutation
adaptation and natural selection
new species is formed.
Isolation definition in speciation
Where an isolation barrier forms between a population dividing the population and preventing gene flow.
Mutation in speciation
A random and spontaneous change in an organisms genes will occur in the divided populations resulting in new alleles being introduced into these species.
Adaptation and natural selection in speciation
Organisms are exposed to selection pressures, which allows organisms with advantageous mutations to reproduce and pass on their genes and organisms with disadvantageous genes to be removed from the gene pool.
Types of speciation
Allopatric and sympatric
Allopatric speciation
Speciation which occurs when the isolation barrier is geographical
Sympatric speciation
Where speciation occurs due to an ecological or behavioural isolation barrier.
Difference between Allopatric and sympatric speciation
Allopatric speciation is brought about by a geographical barrier, whereas sympatric is brought about by an ecological or behavioural barrier.
Allopatric speciation occurs when organisms are physically separated, whereas sympatric occurs when organisms are isolated in the same area without physical separation.
Allopatric produces new species slowly due to natural barriers needing to form and species to be reintroduced to each other, whereas sympatric produces new species quickly.
