Test 5

Biotechnology, Immune System, Mutation, Gene pools and Natural Selection

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?

1. Deletion: part of a chromosome is lost

2. Duplication: a section of chromosome occurs twice

3. Inversion: breaks occur in a chromosome and the broken piece joins back in, but inverted (the wrong way around)

4. Translocation: part of a chromosome breaks off and is re-joined to the wrong chromosome

5. 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?

1. Errors in replication

2. During cell division

3. 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?

1. Mutations

2. Random Genetic Drift

3. Gene Flow

4. 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:

1. Geographical barriers: mountain range, river, that keep populations physically separated

2. 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

1. There is variation in the population due to existing mutation

2. There is competition between individuals

3. Selection pressures make some genetic traits more favourable for survival

4. Those with the traits survive and reproduce, those without will die

5. Favourable allele is passed onto offspring, unfavourable allele is not passed on

6. 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?

1. The B-cell which is specific to the antigen gets sensitised, enlarges and divides into differentiated b-cell clones and memory cells

2. The differentiated b-cells become plasma cells which mass produce the specific antibody

3. The antibodies (protein immunoglobulin):

   1. Combine with pathogens and inhibit it

   2. Bind to virus and prevent entry

   3. Make it easier for phagocytosis by:

      1. Coating bacteria

      2. Causing agglutination

      3. 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?

1. The infected cell (or antigen presenting cells) presents the antigen to the specific T-cell

2. The sensitised T-cell enlarges and becomes differentiated T-cell clones and memory cells

3. The T-cell clones differentiate into:

   1. Killer T-cells

   2. Helper T-cells: sensitises more lymphocytes and increase macrophage activity

   3. 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

1. Determine biological relationships

2. Trace ancestry

3. Identify victims and criminals

4. Identify disaster victims

5. Predict disease

What are the steps of DNA profiling?

1. Obtain DNA sample

2. Treat DNA sample with restriction enzymes

3. 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

4. DNA is negatively charged and will be repelled by the negative electrode and attracted by the positive electrode

5. 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?

1. Obtain DNA sample

2. Mix DNA sample, taq polymerase, free nucleotides and primer (short single stranded DNA which bind before the target DNA to be amplified)

3. Add mixture to thermocycler which moves through 3 temperatures 30+ times

   1. Denaturation (96 degrees Celsius): Hydrogen bonds break, separating the strands of DNA

   2. Annealing (55 degrees Celsius): The single stranded primers attach to both strands of separated DNA

   3. Extension/Elongation (72 degrees Celsius): Taq polymerase attach complimentary nucleotides to both templates starting from the site of primer