21.4 - Locating Genes, Genetic Screening, And Counselling Flashcards
How has recombinant DNA technology contributed to diagnosing and treating genetic disorders?
Recombinant DNA technology enables the diagnosis and treatment of genetic disorders by allowing scientists to locate specific DNA sequences (genes). This is achieved using labelled DNA probes and DNA hybridisation.
What is a DNA probe, and what are the two main types?
- A DNA probe is a short, single-stranded length of DNA with an identifiable label. The two most commonly used probes are:
1) Radioactively labelled probes – Made of nucleotides containing the isotope 32P, identified using X-ray film exposed by radioactivity.
2) Fluorescently labelled probes – Emit light under certain conditions, e.g., when binding to the target DNA sequence
How are DNA probes used to identify specific alleles of genes?
DNA probes identify particular alleles by:
- Designing a probe with base sequences complementary to the allele of interest.
- Separating the double-stranded DNA being tested.
- Mixing the separated strands with the probe, which binds to the complementary sequence (DNA hybridisation).
- Identifying the probe’s binding site via radioactivity or fluorescence
What is DNA hybridisation, and how does it occur?
- DNA hybridisation occurs when a single-stranded section of DNA or RNA combines with a complementary DNA strand. The process involves:
1) Denaturation – Heating the DNA to separate the two strands.
2) Annealing – Cooling the mixture to allow complementary bases to recombine.
3) If complementary DNA strands are present in the mixture, they may hybridise with the separated strands.
How are DNA probes and hybridisation used to locate specific alleles, such as a mutant allele causing a genetic disorder?
1) Determining the base sequence of the mutant allele using DNA sequencing or genetic libraries.
2) Producing a DNA fragment with complementary bases to the mutant allele.
3) Creating multiple copies of the probe using polymerase chain reaction (PCR).
4) Attaching a marker (e.g., fluorescent dye) to the probe.
5) Heating the patient’s DNA to separate strands.
6) Cooling the DNA in a solution containing probes.
7) If the mutant allele is present, the probe will bind due to complementary sequences.
8) Washing away unattached probes.
9) Detecting fluorescently labelled hybridised DNA using a special microscope.
Why is genetic screening important, and how does it work?
Genetic screening identifies individuals carrying mutant alleles, allowing them to assess the risk of passing genetic disorders to offspring. The process involves:
1) Screening individuals with a family history of genetic diseases.
2) Determining carrier status for recessive disorders.
3) Providing genetic counselling to discuss the risks and implications.
4) Using DNA probe arrays to screen for multiple disorders at once by detecting fluorescence.
How is genetic screening used to detect oncogenes and cancer risks?
Genetic screening helps detect:
- Oncogene mutations – Determines the type of cancer and the best treatment (e.g., drugs or radiotherapy).
- Predictive gene changes – Identifies patients most likely to benefit from specific treatments. Example: Herceptin for breast cancer.
- Single cancer cells – Detects patients at risk of relapse from leukaemia.
Individuals with a mutated tumour suppressor gene, increasing cancer risk.
What is personalised medicine, and how does genetic screening contribute to it?
Personalised medicine tailors treatments based on an individual’s genotype. Genetic screening helps:
- Determine the optimal drug dosage to ensure effectiveness.
- Avoid harmful medications or unnecessary prescriptions.
- Improve painkiller efficacy by checking for genes affecting enzyme function.
- Assess the risks and benefits of supplements, such as vitamin E for diabetics.
What is genetic counselling, and how does it assist individuals?
- Genetic counselling provides information and support to individuals regarding inherited diseases. Key roles include:
- Researching family history of genetic disorders.
- Advising on the probability of passing on conditions.
- Explaining the medical, emotional, and economic impacts of genetic diseases.
- Suggesting further genetic tests (e.g., IVF embryo screening).
- Guiding cancer patients on treatment options based on genetic screening.
How does genetic counselling help individuals with a family history of sickle-cell anaemia?
- If a mother carries the sickle-cell allele and the father does not, their children will be carriers but unaffected. However, if both parents carry the allele:
- 25% chance the child will inherit sickle-cell anaemia.
- 50% chance the child will be a carrier.
- 25% chance the child will be unaffected.
- The counsellor provides information on the disease’s impact and potential genetic testing options.
