4. Genetic Variation, Natural Selection, Diversity Flashcards
Why do organisms show genetic variation?
- Random mutations
- Meiosis
- Random fertilisation
Continuous variable
Individuals can lie anywhere between two extremes
Discrete variable
Individuals fall into categories
Population
All of the organisms of the same species living in a particular area at a particular time
Gene pool
The total number of different alleles in a population at a particular time.
A population with a wider variety of alleles has a greater genetic diversity
Allele
Different versions of a gene.
How do new alleles arise?
Due to mutations
Phenotype
The characteristics an organism has as a result of its combination of alleles
Species
Organisms that can interbreed to produce fertile offspring
What is the only way competition for resources can be established?
If organisms produce more offspring than can be supported by the available resources
Population graph axes & shape
x = time
y = number of individuals of a species
shape = S shaped (like cumulative freq graph)
3 stages of a population graph
- Slow growth
- Rapid growth: no natural selection so no competition for resources (plenty of them)
- Stable population: now competition for resources, leading to natural selection
What is carrying capacity and how is this shown on a population graph?
The maximum population that the environment can support
Shown where the graph levels off
Natural selection depends upon the following factors:
- Producing more offspring than can be supported by available resources
- Genetic variation within the population
- Genetic variation leads to different phenotypes which may be advantageous or disadvantageous
3 different phenotypes
Physical
Behavioural
Biochemical
Examples of physical phenotyes
Colour
Examples of behavioural phenotypes
Hedgehogs rolling into balls
Examples of biochemical phenotypes
Haemoglobin’s affinity for oxygen changes in different environments
Natural selection in a nutshell
- More organisms born than can survive
- Variation amongst organisms: some have alleles that make them better adapted to the environment than others
- Selection pressure act on the population & organisms compete for limited resources
- Better adapted organisms out-compete the less well-adapted ones and so survive & breed, passing on their advantageous alleles to future generations
- Over many generations the advantageous alleles become more common in the gene pool, whilst disadvantageous ones become less common
Two types of selection pressures
Biotic & abiotic
Examples of biotic selection pressures
Predators
Prey
Disease
Habitat
Mates
Examples of abiotic selection pressures
Sunlight
Minerals
Temperature
Water
Physical space
The two types of selection on evolution are…
- Stabilising selection
- Directional selection
Normal distribution graph axes & shape
x = the variable (e.g. height)
y = frequency
shape = hump/mountain
Explain shape of normal distribution graph
Hump: most individuals have characteristics around the mean value
Plateaus at the ends because fewer individuals have extreme characteristics
What is stabilising selection?
Selection against extremes of the phenotype range
Where does stabilising selection occur?
Stable environments/when the environmental conditions are stable
What is directional selection?
Selection for one extreme of the phenotypic range
Where does directional selection occur?
When the environmental conditions change
A notable example of directional selection is…
antibiotic resistance!
Use of antibiotics puts directional selection pressure on the bacterial population
What are antibiotics?
Chemicals that target molecules & structures ONLY found in prokaryotic cells (70S ribosomes/murein cell wall)
They can also be enzyme inhibitors targeting bacterial enzymes
Reasons for antibiotic resistance
- Antibiotics used to treat illnesses that are trivial/short lived
- Doctors accept patients’ demands for antibiotics even if they aren’t necessary
- Not finishing a course of antibiotics
- Stockpiling antibiotics from previous prescriptions then using them in smaller doses
- Using them in agriculture to prevent disease particularly in intensively reared animals
Describe what a petri dish used to test for antibiotic resistance looks like
- Disks of paper soaked in different antibiotics
- Bacteria growing on agar plate
- Clear space around disks indicate no bacteria growing there, so the larger the area around a disk of paper is the more effective of an antibiotic it is
Example of stabilising selection
Human birth weights
Define taxonomy
The study of classification
Define classification
Grouping living organisms
Define artificial classification system
Grouping organisms according to differences that are seen as useful or important and that time
Define analogous characteristics (and give an example)
Similar functions but different evolutionary origins (e.g. wings in insects & birds; eyes in land mammals vs. crustaceans)
Define natural classification system
Hierarchical (groups within groups/order)
Based on shared homologous characteristics which have been derived from evolutionary ancestors
Another name for natural classification system is…
phylogenetic classification system
What is the advantage of a natural system over an artificial system?
Natural systems are based on evolutionary origins rather than visual observations
Define homologous characteristic (& give an example)
Body parts of organisms that have the same anatomical features thus indicating a common ancestor or developmental origin
(e.g. forelimbs of humans, cats, bats)
How can we find out how closely related two species are?
Through comparing the same gene in different species (comparing DNA sequences), specifically through comparing nucleotide sequence of the gene or the amino acid sequence of the protein
Why is cytochrome C an ideal gene that could be used to compare different species?
Cytochrome C is an important gene for a protein used in respiration. The vast majority of species have a version for the cytochrome C gene.
The seven taxa/groups in order:
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
(do keep penis clean or forget good sex!!!)
The three domains are:
- Bacteria
- Archaea
- Eukarya
5 characteristics of bacteria domain
- prokaryotic
- no membrane-bound organelles
- 70s ribosomes
- cell walls made of murein
- unicellular
5 characteristics of archaea domain
- prokaryotic
- contain genes and proteins that are more similar to eukaryotic cells
- membrane structure different from bacteria
- cell walls not made from murein
- RNA polymerase very different from bacteria
3 features of eukarya domain
- contain membrane bound organelles such as mitochondria and chloroplasts
- contain a nucleus
- 80s ribosomes`
The 4 kingdoms within the eukarya domain are…
- Protoctista
- Fungi
- Plants
- Animals
Protoctista feature
Not multicellular (e.g. algae amoeba)
Fungi features
- Chitin cell wall
- Saprotrophic nutrition: secrete extracellular enzymes to digest stuff then absorbed back inside
Plants features
- All multicellular
- Photosynthetic
- Cellulose cell wall
Animals features
- All multicellular
- No cell wall
- No photosynthesis
Define species
Can interbreed to produce living and fertile (viable) offspring
Problems with the definition of a species
Doesn’t apply to organisms that reproduce asexually
Some plants can be hybridised to produce new species that can produce fertile offspring too!
Advantage of binomial naming system over using common names
Overcomes language barriers
Avoids muddling things up
Courtship behaviour overview
Courtship behaviour is an important example of an inborn (genetic) behaviour that is essential for reproduction, and therefore the survival of a species.
4 main purposes of courtship behaviour
Identify a mate of the same species
Identify a mate that is capable of breeding
Synchronises mating with female’s fertility cycle
Forms or strengthens a pair bond
Define phylogeny
The study of the evolutionary relationships between organisms
What are phylogenetic trees nowadays based off of?
Comparisons of gene or protein sequences
What do intersections/junctions in phylogenetic trees represent?
Common ancestor
The three aspects of biodiversity are…
Species diversity
Genetic diversity
Ecosystem diversity
The two aspects of species diversity are…
Species richness
Relative number of individuals of each species
Define species richness
Number of different species in an area
Formula for species diversity (Simpson’s diversity index)
N(N-1) / Σn(n-1)
N = total # of organisms of all species
n = total # of organisms of each species
9 ways in which agriculture could impact biodiversity
- Destruction of natural habitats to provide land for agriculture
- Monoculture
- Selective breeding: reduces genetic diversity
- Crops out-compete other species
- Space available for other species is reduced
- Pesticides kill other species
- Eutrophication
- Over grazing
- Removal of hedgerows to farm large fields
Why might maintaining biodiversity be in the farmer’s best interests?
Insects are required for pollinating plants which is how plants reproduce (agriculture)!
How can farmers help to maintain biodiversity without impacting on their ability to produce enough food?
- Maintain hedges instead of fences
- Reduce pesticide use - use biological control instead
- Don’t overuse fertilisers: use crop rotation to maintain soil quality
- Maintain existing ponds
- Plant trees
What are the limitations of using observable characteristics to investigate diversity?
• Physical characteristics can change according to environment e.g. skin colour
• Organisms can have similar characteristics but by chance/coincidence: these are analogous not homologous
What is now the best way of investigating diversity?
Using molecular characteristics - comparing DNA, mRNA and amino acid sequences in specific proteins
Process of immunological comparisons of proteins (using humans and rabbits as an example)
- Human serum containing human proteins is injected into rabbit
- Rabbit immune system recognises human proteins as foreign, and produces antibodies specific to the human proteins
- Rabbit serum contains antibodies produced by the rabbit
- Rabbit serum injected into serum from blood of other species
- The more similar the other species’ proteins are to human proteins, the more the rabbit antibodies bind to them and produce precipitate
Interspecific vs intraspecific variation
Interspecific: differences between different species of organisms
Intraspecific: differences between members of the same species
Quantitative investigations of variation within a species involve:
- collecting data from random samples
- calculating a mean value of the collected data and the standard deviation of that mean
- interpreting mean values and their standard deviations
Why is sampling often used when investigating diversity?
Investigating small parts rather than the whole ecosystem: ecosystems are massive!
Rarely possible to record data about every individual in a population
Define representative sample
A sample that captures the full picture of an ecosystem
What measures can be taken to ensure that sampling is representative?
- Random sampling: avoids sample bias
- Large sample: enough quadrats
- Use statistical analysis of data from the sample
What does it mean if standard deviation bars overlap on a graph?
Differences between mean is NOT significant
How to calculate degrees of freedom
(n1 + n2) - 2
When do you reject the null hypothesis?
Calculated value BIGGER than tabulated value
What does it mean when you reject the null hypothesis at the x% significance level?
Less than x% probability that the differences between the two sets of data are due to chance
What does a small p value for a T test mean?
We can be certain that the pattern we’re seeing isn’t due to chance, but rather a solid relationship.
Define genetic diversity
Number of different alleles in a population
