Gene technologies 2 Flashcards
(23 cards)
Suggest how recombinant DNA technology can be useful
Medicine:
* GM bacteria produce human proteins (e.g. insulin for type 1 diabetes). This is more ethical than using animal proteins and less likely to cause allergic reactions
* GM animals / plants produce pharmaceuticals, which is cheaper than lab produced drugs
* Gene therapies
Agriculture:
* GM crops resistant to herbicides, so that only weeds are killed when crops are sprayed with herbicide
* GM crops resistant to insect attack, reduce need for use of insecticide
* GM crops with added nutritional value (e.g. Golden rice contains more vitamin A)
* GM animals with increased growth hormone production
Industry:
* GM bacteria produce enzymes used in industrial processes and food production
Describe gene therapy
Introduction of new DNA into cells, often containing healthy / functional alleles, to overcome effect of faulty / non-functional alleles in people with genetic disorders e.g. cystic fibrosis
Suggest some issues associated with gene therapy
- Effects are short term as modified cells (e.g. T cells) have a limited lifespan, so the individual requires regular treatment
- Body may start an immune response against genetically modified cells or viruses due to recognition of foreign antigens
- Long term effect not known - side effects could include cancer
Suggest why humanitarians might support recombinant DNA technology
- GM crops increase yields, increasing global food production and reducing risk of famine and malnutrition
- Gene therapy has potential to cure many genetic disorders
- Using GM plants to produce pharmaceuticals makes medicines available to more people as medicines are cheaper
Suggest why environmentalists and anti-globalisation activists might
oppose recombinant DNA technology
- Recombinant DNA may be transferred to other plants, could result in herbicide resistant ‘superweeds’
- Potential effects on food webs, reducing biodiversity
- Large biotech companies may control the technology and own patents
What are DNA probes?
Short, single stranded pieces of DNA with a base sequence complementary to bases on target allele. They are usually labelled with a fluorescent or radioactive tag for identification.
Suggest why DNA probes are longer than just a few bases
A sequence of a few bases would occur at many places throughout the genome, and longer sequences are only likely to occur in the target allele
What is DNA hybridisation?
The binding of a single stranded DNA probe to a complementary single strand of DNA, forming hydrogen bonds between complimentary base pairs
Explain how genetic screening can be used to locate specific alleles of gene
- Extract DNA and amplify by PCR
- Cut DNA at specific base sequences (either side of target gene) using restriction enzymes
- Separate DNA fragments using gel electrophoresis
- Transfer to a nylon membrane and treat to form single strands with exposed bases
- Add labelled DNA probes which hybridise / bind with target alleles (& wash to remove unbound probe)
- To show bound probe, expose membrane to UV light if a fluorescently labelled probe was used OR use autoradiography (expose to X-ray film) if a radioactive probe was used
What is gel electrophoresis?
A method used to separate nucleic acid (DNA / RNA) fragments or proteins according to length / mass (number of bases / amino acids) AND charge (DNA is negatively charged due to phosphate groups and protein charge varies based on amino acid R groups)
Explain how gel electrophoresis can be used to separate DNA fragments
- DNA samples are loaded into wells in a porous gel and covered in buffer solution (which conducts electricity)
- Electrical current is passed through, and DNA is negatively
charged so moves towards the positive electrode - Shorter DNA fragments travel faster so travel further
How can data showing results of gel electrophoresis be interpreted?
- Run a standard with DNA fragments / proteins of known lengths under the same conditions
- Compare to position of unknown DNA fragments / proteins to estimate their size
- Shorter DNA fragments/ proteins travel further
Describe examples of the use of labelled DNA probes
- Screening patients for heritable conditions (e.g. cystic fibrosis)
- Screening patients for drug responses (some alleles code for enzymes involved in drug
metabolism that enable better responses to certain drugs) - Screening patients for health risks (some alleles predispose patients e.g. to high blood cholesterol)
Describe the role of a genetic counsellor
- Explain results of genetic screening, including consequences of a disease
- Discuss treatments available for genetic condition
- Discuss lifestyle choices / precautions that might reduce risk of a genetic condition developing e.g. regular screening for tumours or a mastectomy
- Explain probability of condition / alleles being passed onto offspring, enabling patients to make informed decisions about having children
What is personalised medicine?
Medicine tailored to an individual’s
genotype / DNA, increasing effectiveness of treatment
e.g. by identifying the particular
mutation or allele causing cancer and treating it with tailored drugs
Evaluate the screening of individuals for genetically determined conditions
and drug responses
For:
* Some people could be heterozygous / carriers (e.g. in families with a history of a disease)
* Can enable these people to make lifestyle choices to reduce chances of diseases developing, to prevent suffering / death
* Allows people to make informed decisions about having their own biological children
* Allows use of personalised medicines, increasing effectiveness of treatment
Against:
* Screening for incurable diseases or diseases that develop later in life (where nothing positive can be done in response) may lead to depression
* May cause undue stress if patient does not develop the disease
* Could lead to discrimination by insurance companies / employers
What are variable number tandem repeats (VNTRs)?
Repeating sequences of bases found within non-coding sections of DNA at many sites throughout an organism’s genome
Why are VNTRs useful in genetic fingerprinting?
Probability of two individuals having the same VNTRs is very low, as an organism’s genome contains many VNTRs and lengths at each loci differ between individuals
Explain how genetic fingerprinting can be used to analyse DNA fragments
- Extract DNA from sample and amplify by PCR
- Cut DNA at specific base sequences (at either side of VNTRs) using restriction enzymes
- Separate VNTR fragments according to length using gel electrophoresis (shorter ones travel further)
- Transfer to a nylon membrane and treat to form single strands with exposed bases
- Add labelled DNA probes which hybridise / bind with complementary VNTRs (& wash to remove unbound probe)
- To show bound probe, expose membrane to UV light if a fluorescently labelled probe was used, or use autoradiography (expose to X-ray film) if a radioactive probe was used
Compare and contrast genetic fingerprinting with genetic screening
- Both use PCR to amplify DNA sample
- Both use electrophoresis to separate DNA fragments
- Both use labelled DNA probes to visualise specific DNA fragments
- Genetic fingerprinting analyses VNTRs whereas genetic screening analyses specific alleles of a gene
Explain how genetic fingerprinting can be used to determine genetic
relationships
More closely related organisms have more similar VNTRs, so will have more similarities in genetic fingerprints. Can be used in paternity testing - father should share around 50% of VNTRs / bands with child (due to inheritance)
Explain how genetic fingerprinting can be used to determine genetic
variability within a population
Differences in VNTRs arise from mutations, so more differences show greater diversity within a population
Explain the use of genetic fingerprinting in the fields of forensic science, medical diagnosis, animal and plant breeding
Forensic science:
* Compare genetic fingerprint of suspects to genetic fingerprint of DNA at crime scene
* If many bands match, the suspect was likely present at the crime scene
Medical diagnosis:
* Some VNTR patterns are associated with an increased risk of certain genetic disorders e.g. Huntington’s
Animal and plant breeding:
* Shows how closely related 2 individuals are, so that inbreeding can be avoided
* Breed pairs with dissimilar genetic fingerprints
