Evolution Flashcards
Species
A group of organisms that can interbreed to produce a fertile offspring
Population
A group of organisms of the same species in a particular space at a particular time
THAT CAN POTENTIALLY INTERBREED
2 main sources of variation
Genetic factors
Environmental factors
To change the phenotype
Primary source of GENETIC variation
Mutations, create new alleles of a gene
When are mutations beneficial?
In a given selection pressure (environmental change), may express a phenotype that benefits possessor to increase chance of survival and therefore reproductive success
Genetic diversity
Number of different alleles of genes in a population
Other sources of genetic variation other than mutations
Meiosis: independent segregation and crossing over
Random fertilisation of gametes
Does the environment impact the phenotype expressed?
Yes
Continuous variation
No distinct categories but a quantitative measurement using a scale eg height in cm
Continuous variation eg height is controlled by how many genes?
A lot
More than discontinuous variation
Is continuous variation strongly influenced by the environment?
Yeah
How is variation in continuous characteristics eg height shown on a graph?
Tend to be in line graphs to show how the data is continuous
Discontinuos/discrete variation
Has distinct categories like blood type or eye colour
Tends to be qualitative
How many genes control discrete variation?
Not many
Is discrete variation affected much by the environment?
No
Natural selection progression 3 stages
Mutation
Selection pressure
Reproduction + Frequency of beneficial allele increases
How does mutation contribute to natural selection?
occurs randomly to create a new allele and increases genetic diversity in a population leading to expression of variety of phenotypes
How does a selection pressure contribute to natural selection?
Organisms with alleles provide selective advantages and so more likely to survive and produce offspring + pass on favourable alleles to next generation
Given a selection pressure in environment
How does, over time, a species evolve following mutation, selection?
Frequency of beneficial alleles rise in gene pool
If beneficial alleles are selected based on advantages, this means species evolve and are……
Adapted to environment
Types of adaptations
Anatomical
Physiological
Behavioural
Anatomical adaptations
Regarding body parts
Physiological adaptations
Regarding body systems
3 types of natural selection
Stabilising
Directional
Disruptive
Stabilising selection
Selection against both extremes of a phenotype
So THE mean phenotype of all species is in the middle of a scale as high frequency of species in population have allele for middle of phenotype
Stabilising selection progression
Mutation leads to creation of variety of alleles leads to expression of variety of different phenotypes
Selection pressure in environment means advantageous allele for (medium level phenotype) is selected
So organisms with this allele more likely to survive and reproduce to pass allele to offspring so this allele increases in frequency in population
Case study for stabilising selection
Birth mass in babies:
Extreme mass babies more likely to die and less likely to pass on alleles for extreme birth mass to their children
So frequency for alleles for extreme mass at birth decreases in population
And mid birth mass has selected advantages etc
Natural selection
The result of Differential survival and reproduction of specific species due to predation, disease and competition for means of survival
Meaning organisms possessing favourable alleles are more likely to survive due to adaptations as a result
How does a mutation lead to natural selection?
Creation of new alleles that increases genetic diversity in a population = variety of phenotypes created
Organisms with alleles for phenotypes that provide selective advantages are more likely to survive and produce offspring + pass on favourable alleles to next generation.
So frequencies of beneficial alleles rise within a gene pool.
Frequency of a specific allele in a population shows…?
Proportion of species in a population that possess this allele
How are frequencies expressed?
As a decimal out of 1
1.0 = 100%
0.4 = 40% of species in population have this allele
Directional selection
Selection in favour of one extreme of a phenotype
So mean phenotype of species in this population lies at one extreme end of a scale
Progression of directional selection
Mutation leads to creation of alleles for an extreme phenotype
Selection pressure in environment means species possessing beneficial extreme allele more likely to survive and reproduce to pass allele onto next gen
So frequency of extreme allele thus extreme phenotype in population BOTH INCREASE
Case study example for directional selection
Antibiotic resistance in bacteria
How does antibiotic resistance occur?
By random mutation, some bacteria have allele for resistance
Use of antibiotics is the selection pressure: non-resistant bacteria die; resistant bacteria more likely to survive to reproduce and pass on their alleles
Frequency of the resistance allele increases in the bacterial population
Frequency of antibiotic resistance increases in the bacterial population;
Is natural selection random?
NO based on selected advantages of specific alleles as a result of selection pressure (predation, disease, competition) BUT THE CREATION OF THESE ALLELES BY MUTATION IS RANDOM
Disruptive selection
When phenotypes of 2 extremes of a scale are selected for ie selected advantages of 2 alleles that encode for an extreme phenotype
Example of disruptive selection
Darker individuals of a species provide more camouflage in shadows but lighter individuals of same species are harder for predators to spot etc
Evolution
Change in allele frequencies in a population
Allele frequency
The number of times a specific allele occurs in a gene pool
Gene pool
All the alleles in a population
Genetic drift
RANDOM changes in allele frequency in a population
Death that reduces allele frequency by random chance
What causes changes in allele frequency thus leads to evolution in a population?
Genetic drift = random changes in allele frequency
Natural selection = alleles with selected advantages increase in frequency
