Miracle or menace? : biotechnology and the third world / by Robert Walgate.

  • Walgate, Robert
Date:
[1990]
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Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Miracle or menace? : biotechnology and the third world / by Robert Walgate. Source: Wellcome Collection.

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    Chapter 4: Plant genetic engineering 53 A FEW BASICS... DNA probes # Extremely sensitive DNA probes can identify the DNA representing a specific gene. # DNA probes exploit the structure of DNA. DNA molecules are composed of two long chains of chemical sub-units wound around each other to form the famous double-helix. # The chemical sub-units of each DNA strand are the letters of the genetic message. There are four types of letter (or base) in DNA — called A, C, G, and T. # The two strands of the DNA molecule are held together by pairing between the bases on each strand. A can only pair with T, and G can only pair with C. This is the base-pairing rule which governs all nucleic acid interactions. # A DNA probe is simply a short length of DNA with a base sequence complementary to a part of one of the strands of the DNA that is being searched for. The probe is synthesised artificially in the laboratory and tagged with some radioactive atom or with a chemical dye that makes it easily detectable. # When it finds its target it sticks to it by complementary base-pairing, making the target readily identifiable. # DNA probes are so sensitive that they can detect their target gene in a tiny amount of material — just a drop of blood from a finger, or a small piece of tissue. to similar genes in other plants, and reveal a constellation of salt-resistance mechanisms. Virginia Walbot, of Stanford University, is studying the responses of rice to cold which, she claims is the main environmental factor limiting rice production, affecting the seedlings. One protein that appears [in response to cold] is very like a drought-response protein. And cold stress leads to wilting, just as drought does [19]. As with salt-tolerance, given the proteins, the corresponding genes may be traced, and the genetic basis of cold-tolerance mapped out. This will aid conventional breeding programmes, as well as offering new genes to transfer between plants by genetic engineering. GENES TO BLOCK OTHER GENES: ANTISENSE RNA This exciting new development has been used to most dramatic effect in blocking a gene whose enzyme product — polygalacturanase — causes the ripening and softening of tomatoes. Genetically engineered tomatoes containing antisense genes have been produced that do not go soft on storage, and so have a longer shelf-life [20]. Antisense RNA is thought to work by preventing the translation of its corresponding sense RNA — the normal messenger RNA produced by a gene. Antisense RNA is a complementary copy of the
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