Nucleic acid blotting yields valuable information in both the research and clinical settings. More than 500 human genetic diseases are attributed to single-gene defects. For example, sicklecell anemia is caused by a simple point mutation in the gene that encodes for the P-chain of hemoglobin (36). By employing short oligonucleotide probes for mutant and normal gene sequences, it is possible to distinguish between the two forms of the gene by Southern blot analysis (37). Pathological gene alterations can also be detected in diseases such as Burkett's lymphoma, Fragile X syndrome, familial hypercho-lesterolemia, the hemophilias, and inborn errors of metabolism (38,39). The Southern blot provides a means of identifying a specific altered gene, thus allowing prenatal detection of many genetic diseases, many of which can be corrected by simply administering the functional protein that should be encoded by the defective gene. The Northern blot provides information on gene expression that might be useful in establishing prognosis in diseases, such as colon cancer (40). During embryonic development, large numbers of genes are switched "on" and "off' in elaborate, defined patterns. This if often true for the process of carcinogenesis as well, in which the expression patterns of specific genes become altered, contributing to the formation of a tumor. Northern blotting allows the expression of a specific gene to be examined so that one can determine if the gene of interest is underexpressed or overexpressed compared to normal. Experimental evidence supports the idea that carcinogen-esis is the result of the loss of a cell or group of cells to control their growth. Such a phenomenon might be the result of overproduction of a growth-stimulatory factor, underproduction of a growth inhibitor, or altered production of cell cycle regulatory molecules.
Nucleic acid blotting permits detailed characterization of a specific gene. Southern blot identify structural abnormalities, whereas Northern blots show gene expression levels and low detection of alternatively spliced transcripts. Despite the development of more rapid PCR-based methods of nucleic acid analysis, traditional nucleic acid blotting remains a valuable tool in many molecular biology laboratories.
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