Cells of a patient are grown as clones in a dish…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Cells of a patient are grown as clones in a dish. A single stranded DNA probe with a radioactive tag is complementary to the normal form of a gene. It is mixed with the DNA of each clone. Then a photographic film is placed over the dish. One clone does not show on the film. It carries a mutated form of the gene.
- What does the probe do to the DNA of a clone with the normal gene?
- Why does the clone with the mutated gene not appear on the film?
- What is the name of the method of photographing the radioactive tag?
- Which other test uses an antigen and an antibody to find an infection?
Need a reminder? The key ideaShow
Gene therapy delivers a normal gene to take over the work of a non-functional one. The first clinical gene therapy, in 1990, was for a four-year-old girl with ADA deficiency, which is caused by the deletion of the gene for adenosine deaminase. Lymphocytes are grown outside the body, given a functional ADA cDNA by a retroviral vector, and returned. They are not immortal, so the infusions are repeated. Very low amounts of a germ can be found early by PCR, which copies the nucleic acid, and by ELISA, which uses antigen and antibody interaction.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) It hybridises, which means that it pairs with the complementary DNA of the normal gene. The radioactive tag shows the place.
Step 2. (b) The mutated gene has a changed sequence. The probe is not complementary to it, so it does not bind, and no tag is present on the film.
Step 3. (c) Autoradiography.
Step 4. (d) ELISA.
Answer: (a) it hybridises; (b) the mutated gene is not complementary to the probe; (c) autoradiography; (d) ELISA.
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