Mutation
Permanent change to a gene or chromosome
Mutant
An organism with a characteristic resulting from a mutation
Mutagen
Agents known to increase the rate at which mutations occur
Somatic Mutation
A mutation that occurs in body cells and does not affect reproductive cells
Germline Mutation
A mutation that occurs in gametes and does not usually affect the individual however the individual produces gametes with changed DNA.
Gene Mutation
A mutation that occurs when there is a change in a single gene
Point Mutation
A change in just one base
Frameshift Mutation
A single base is added or deleted from DNA, which shifts the reading of codons by one base
Lethal Recessive
A recessive mutation not masked by a dominant (normal) allele that can be lethal
Chromosomal Mutation
A mutation that occurs when there is a change in the whole or part of a chromosome causing a change in a few nucleotide bases
What are the five types of chromosomal mutations and their definitions?
Deletion: part of a chromosome is lost
Duplication: a section of chromosome occurs twice
Inversion: breaks occur in a chromosome and the broken piece joins back in, but inverted (the wrong way around)
Translocation: part of a chromosome breaks off and is re-joined to the wrong chromosome
Non-disjunction: during meiosis, a chromosome pair does not separate and so one daughter cell has one less chromosome (monosomy) and one has one extra (trisomy)
Aneuploidy
Any change in the chromosome number
What are the three causes of mutations?
Errors in replication
During cell division
From damage caused by mutagens
Species
Organisms belonging to the same species are capable of producing fertile offspring under natural conditions
Population
A group of organisms of the same species living together in a particular place at a particular time
Gene Pool
The sum of all the alleles in a given population, it can change over time
Allele Frequency
A measure of how often a particular allele appears in a gene pool, given as a percentage
Evolution
The change in phenotypes in a population over time, this change in phenotypes is caused by a change in genotypes
What are the four mechanisms that allow frequencies to change?
Mutations
Random Genetic Drift
Gene Flow
Selection Pressure
What is the definition of random genetic drift and an example?
The random, non-directional change in allele frequencies of a population from one generation to the next. It will have a large impact on smaller populations.
Example: The frequency of different blood types varies by location
What is the Founder Effect?
A type of random genetic drift where a small group of individuals move away from the main group and colonise a new area.
By random change, the founder population may have different allele frequencies and/or decreased genetic variation compared to the main population.
Over generations, the allele frequencies of the population in the new area will vary from those of the mainland population
What is the Bottleneck Effect?
A type of random genetic drift where a catastrophic event dramatically reduces the population size, the surviving population is random
When the surviving population repopulates, the allele frequencies reflect that of the survivors, as opposed to the original population
What is the definition of gene flow, the two types of barriers and examples?
The movement of genetic material from one population to another
Occurs when individuals migrate between populations
The migrants bring in their alleles and change the allele frequency of the population they moved into
Barriers to gene flow prevent interbreeding between populations. The isolation can lead to separate gene pools forming. Barriers include:
Geographical barriers: mountain range, river, that keep populations physically separated
Sociocultural barriers: economic status, social position, this stops certain groups of individuals breeding with others
What’s selection pressure and the six steps?
The factors that increase or decrease the chance of an individual of surviving or reproducing
If the environment favours a particular characteristics then more alleles for that trait will be passed onto the next generation
This will result in the change in the frequency of that allele that was selected, over generations the frequency of the allele that was selected for will increase
There is variation in the population due to existing mutation
There is competition between individuals
Selection pressures make some genetic traits more favourable for survival
Those with the traits survive and reproduce, those without will die
Favourable allele is passed onto offspring, unfavourable allele is not passed on
Over generations, the allele frequency of the favourable trait increases while allele frequency of the unfavourable trait decreases and may die out
Genome
The complete set of genetic information of an organism
Hereditary Disease
Disease caused by defective genetic information being transmitted from one generation to another, often caused by mutations to the normal DNA.
A mutation is a disruption to the healthy nucleotide sequence in DNA
What are the two specific immune responses of the third line of defence?
Humoral Response (B-cells)
Cell Mediated Response (T-cells)
Where are B cells produced and matured?
Bone marrow
Where are T-cells produced, matured and found?
Produced in bone marrow
Matured in the thymus.
Mostly found in lymph nodes
What are the steps of a humoral response?
The B-cell which is specific to the antigen gets sensitised, enlarges and divides into differentiated b-cell clones and memory cells
The differentiated b-cells become plasma cells which mass produce the specific antibody
The antibodies (protein immunoglobulin):
Combine with pathogens and inhibit it
Bind to virus and prevent entry
Make it easier for phagocytosis by:
Coating bacteria
Causing agglutination
Making substances insoluble
However once a pathogen enters a cell, it can’t be detected by a humoral immune response.
What are the steps of a cell-mediated response?
The infected cell (or antigen presenting cells) presents the antigen to the specific T-cell
The sensitised T-cell enlarges and becomes differentiated T-cell clones and memory cells
The T-cell clones differentiate into:
Killer T-cells
Helper T-cells: sensitises more lymphocytes and increase macrophage activity
Suppressor T-cells: inhibit B and T cell activity
What is the initial exposure?
The primary response takes time (approx. 2 weeks) and results in low amounts of antibodies
What is the secondary exposure?
The secondary response is quick (approx. 2 days) and results in high amounts of antibodies
What is humoral-mediated immunity’s mechanism, cell type, mode of action and purpose?
Mechanism: Antibody-mediated
Cell type: B lymphocytes
Mode of action: Antibodies circulating in serum
Purpose: Defence against extracellular pathogens e.g. extracellular bacteria, circulating virus
What is cell-mediated immunity’s mechanism, cell type, mode of action and purpose?
Mechanism: Cell-mediated
Cell type: T lymphocytes
Mode of action: Antibodies circulating in serum
Purpose: Defence against intracellular pathogens e.g. viruses and fungi, intracellular bacteria
What are the four types of immunity?
Natural Active: Antigens enter the body naturally; body produces antibodies, killer T-cells and memory cells
Natural Passive: Antibodies pass via placenta or breast milk, is short term protection
Artificial Active: Antigens are introduced in vaccines; body produces antibodies, killer T-cells and memory cells
Artificial Passive: Preformed antibodies in immune serum are injected, is short term protection
Immunity
The ability to resist organism/disease by producing a faster and a more intense response to fight off the organism/disease
What are the four types of vaccine?
What is the use of DNA profiling (DNA fingerprinting)?
To determine whether a sample of DNA came from a given individual by comparing size fragments from different samples
Determine biological relationships
Trace ancestry
Identify victims and criminals
Identify disaster victims
Predict disease
What are the steps of DNA profiling?
Obtain DNA sample
Treat DNA sample with restriction enzymes
DNA samples are then loaded into wells on a gel covered in buffer at the negative electrode (gel acts as a sieve, allowing smaller fragments to move faster than large fragments)(buffer maintains the pH of the DNA and has free electrons which allows electricity to run through it
DNA is negatively charged and will be repelled by the negative electrode and attracted by the positive electrode
Bands/different size fragments are analysed
Restriction enzymes
Recognise a specific sequence of nucleotides and cut the DNA at this sequence resulting in DNA being cut into different size fragments
What is PCR?
Polymerase Chain Reaction is a process that allows rapid duplication of the DNA sample (amplification).
What are the steps of PCR?
Obtain DNA sample
Mix DNA sample, taq polymerase, free nucleotides and primer (short single stranded DNA which bind before the target DNA to be amplified)
Add mixture to thermocycler which moves through 3 temperatures 30+ times
Denaturation (96 degrees Celsius): Hydrogen bonds break, separating the strands of DNA
Annealing (55 degrees Celsius): The single stranded primers attach to both strands of separated DNA
Extension/Elongation (72 degrees Celsius): Taq polymerase attach complimentary nucleotides to both templates starting from the site of primer