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Medicine gene uses
AQA A-level biology gene technology year 13
| Term | Definition |
|---|---|
| Gene therapy | Correcting damaged genes in somatic cells using recombinant gene technology to insert a copy of the defective gene into the cell by transfection |
| Which cell type is gene therapy legally not allowed to be used for | Gametes. Due to concern of people altering gametes to create a “perfect human” rather than just preventing genetic diseases from being inherited |
| Medical issues with gene therapy | Needs to be repeated often & since vectors for humans can be quite invasive this can lead to immune complications |
| Why cystic fibrosis is an ideal candidate for gene therapy | Caused by 3-base deletion, just 1 gene, affects easily accessible part of body, sequence is known, relatively common, function of affected protein (chloride ion channel) is know |
| How being heterozygous for cystic fibrosis could be advantageous | Co-dominant, causes some chloride ion channels to be disrupted which gives some cholera resistance since cholera affects chloride ion channels |
| Gene therapy vectors: adenoviruses | Target genes are loaded onto harmless adenoviruses. The genes released would usually either be broken down or cause overblown immune responses. Even with promoter regions attached, they can’t be expressed from the cytoplasm |
| Gene therapy vectors: liposomes | Genes loaded into phospholipid vesicles & diffused into cells. Administered to 12 children with Severe Combined Immune Deficiencies (SCID) with very high success rate however also a very high rate of leukaemia |
| DNA probe | Small single-stranded DNA length complimentary to a section of desired sequence bound to a visible label (radioactive or fluorescent) |
| How DNA probe works | Anneals to section of genome which expresses desired gene by hybridisation & is run through either agarose or polyacrylamide gel using electrophoresis & will show a luminous band if desired sequence is present while unbound probes are removed from the gel |
| Electrophoresis | DNA is negatively charged due to dissociated hydrogen ions on phosphates & in a buffered solution will move towards a cathode through porous gel, gathering in dyed bands according to DNA size along the way allowing specific sequences to be separated |
| How DNA probes predict reaction to painkillers | Liver enzymes metabolise active chemicals in painkillers to cause effect but these enzymes can be different depending on genomes causing some people to react badly & probes screen to see if people have the correct genome for the painkiller |
| How DNA probes predict reaction to breast cancer chemotherapy | 20% of breast cancer cells have increased HER2 receptor & drug Herceptin can bind to these to prevent proliferation but in 80% of cases it causes side effects with few benefits & probes can detect if the correct genes are present |
| Prenatal genetic testing & ethical considerations | Parents’ DNA is tested for specific harmful sequences with DNA probes. Can’t give gametes gene therapy so no cure for genetic disease in children but gives parents guilt of passing down genetic diseases if they try for a baby |
| Preimplantation genetic diagnosis (PGD) & ethical considerations | Totipotent stem cell removed from embryo before blastocyst forms & is tested with DNA probes. People might be against “damaging” and embryo |
| Amniocentesis | Amniotic fluid removed through long needle & tested with DNA probes. Foetus will be more developed so parents will need to decide whether to bring it to term or abort it, this is difficult if they struggled to become pregnant & have grown attached to it |
| Variable Number Tandem Repeats (VNTRs) | Small repeated units of non-coding DNA between genes & at the end of chromosomes up to 300 base-pairs long that vary massively between people in length & pattern. Can be used to identify people as a genetic fingerprint |
| Genetic fingerprinting: Extraction & digestion | Obtaining a sample of DNA from animal tissue & running PCR to obtain a large amount. Then it is cut into small fragments using the same specific endonucleases |
| Genetic fingerprinting: Separation & hybridisation | Fragments are separated according to size by gel electrophoresis then alkali is added to separate double strands. DNA probes complimentary to the VNTRs anneal under correct temperatures & pH |
| Genetic fingerprinting: Development & interpretation | Bands showing fluorescent probes are scanned into a machine. This identifies the length & pattern of the VNTRs by measuring distances travelled during electrophoresis & compares it to other samples such as those of suspects or family members |
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Study_B
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