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The Cystic Fibrosis Gene

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The Cystic Fibrosis Gene

Cystic fibrosis is an inherited autosomal recessive disease that exerts its main effects on the digestive system and the lungs. This disease is the most common lethal genetic disorder in Caucasians, affecting one out of 2,500. On the bioethical front, CF was the first human genetic disease to be cloned by geneticists. The intent of this paper is to describe how the cystic fibrosis gene was identified, how the gene is defective, its physical manifestations, and to discuss possible treatments of the disease.

The classical approach to finding the gene that is responsible for causing a genetic disease is to first characterize the bio-chemical defect within the gene, then to identify the mutated protein in the gene, and finally to locate the actual gene. However, this classical approach proves to be impractical when searching for the CF gene. To find the gene responsible for CF, the principle of "reverse genetics" is applied. Scientists accomplish this by linking the disease to a specific chromosome. After this linkage, they isolate the gene of interest on the chromosome, and then test its product. Before the disease can be linked to a specific chromosome, however, a marker needs to be found that will always travel with the disease. This marker is known as a Restriction Fragment Length Polymorphism, or RFLP for short. RFLP's are varying base sequences of DNA in different individuals which are known to travel with genetic disorders. The RFLP for cystic fibrosis was first discovered through somatic cell hybridization (cell fusing) and southern blot electrophoresis (gel separation of DNA within an electric field). By using these techniques, three RFLP's were discovered for CF: Doc RI, J3.11, and Met. Utilizing hybridization (rapid heating and cooling of RNA with denatured DNA so that the RNA permanently associates with the DNA,) scientists discovered the CF gene to be located on the long arm of chromosome 7q. Soon after identifying these markers, another marker was discovered that frequented more ...

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...ides. This known as gene therapy.

A drastically different approach taken in an attempt to cure cystic fibrosis, performed as a method of preventive medicine, involves correcting the disease while the affected "person" is still an embryo. Test tube fertilization from affected parents and gene diagnosis during embryonic development can be accomplished through a biopsy of a cleavage-stage embryo and amplification of DNA from single embryonic cells. After this treatment, only unaffected embryos would be selected for implantation into the uterus. Unfortunately however, affected embryos would be discarded.

These treatments are all remarkable breakthroughs in medical science and provide geneticists with a highly positive outlook, but they are nowhere near the miracles yet to come with more research. Since cystic fibrosis is the most common lethal genetic disorder among Caucasians, intense research efforts towards better treatments and its cure are invaluable. The discoveries made from researching this disease may very well help the treatment or cure of other, unrelated diseases.
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