Natural Selecion And Speciation Flashcards
What is natural selection?
The process that leads to evolution
What is evolution?
Evolution is the change in frequencies of alleles of a population, over many generations
Describe the process of natural selection (5 marker)
A population has variation
This is due to random mutations that lead to new favourable allleles of a gene
The allele gives an organism a phenotype that has a selective advantage in the environment
The organisms with the advantageous allele is more likely to survive, and reproduce more offspring
Passes on the advantageous allele too next generations
The frequency of the advantageous allele increases over many generations
STATE THE TYPE OF NATURAL SELECTION (DISRUPTIVE, DIRECTIONAL OR STABILISING)
State the three types of natural selection, and the differently environments that they occur in
Directional- an environment that has changed
Stabilising- an environment that stays the same
Disruptive- fluctuating environment
How can natural selection be show?
On a graph with phenotypes against frequency, and initially shows a bell curve with a normal distribution
Describe what happens in directional selection, and how it affects the graph
Occurs when an environment has changed
It acts against one of the extreme phenotypes in a range of different phenotypes, and favours the other
Causes the mode to change
The frequency of the most successful phenotype increases
Describe what happens during stabilising selection, and how it affects the graph
Occurs when there is no change in environment
It acts to prevent change, as is acts against both extremes in a range of different phenotypes
The mode stays the same, but the range and standard deviation of phenotypes decreases
The frequency of alleles that is adapted to the environment increases
Describe what disruptive selection is, and how it affects the graph
Occurs in an environment that fluctuates
It favours both extremes in the range of phenotypes, so the intermediate/ middle phenotype is less likely to survive and reproduce
Acts against the middle/ intermediate phenotype
The graph goes from having one peak to having two peaks either side
What is selective pressure?
Environmental factors that affects an organisms ability to reproduce and survive
What is a species?
A group of organisms with similar characteristics that can reproduce to produce fertile offspring
What is speciation?
The process where one gene pool gives rise to more than one gene pool
What are the two types of speciation?
Sympatric and allopatric
Describe what allopatric speciation is (5 marker)
Two populations of the same species are geographically isolated due to a physical barrier
two populations are unable to reproduce
Different environments, different selection pressures
Different mutations, formation of advantageous alleles that gives organisms a phenotype that is more likely to survive and reproduce
The allele frequencies in each population change over many generations
The genotypes of the two populations become so different that they cannot reproduce to produce fertile offspring
Two district species created
Describe what sympatric speciation is (5 marker)
Two populations of the same species inhabit the same area, but evolve into different species
Random mutations occur in some organisms, giving them phenotypes that prevent them from reproducing with organisms that do not carry the mutated gene
Reproductive isolation
Reproduction causes different allele frequencies to change in each population
Disruptive natural selection
Eventually genotypes so different they cannot reproduce to produce fertile offspring
Two distinct species
What type of natural selection Gene technology occurs in sympatric speciation?
Disruptive selection
What are the types of reproductive isolation that occur in sympatric isolation?
Seasonal isolation- member of two populations reproduce at different times of the year
Behavioural isolation- members of the same population have different courtship behaviours
Mechanical isolation- anatomical differences prevent two organisms from mating or interbreeding
