cystic fibrosis. They occur because of the strong influence of a mutation in a single gene. Using the tremendous amounts of information about the human genome made available by the Human Genome Project, scientists are now dissecting the genetic components of complex disorders, such as diabetes and heart disease, that come about as a result of both genetic and environmental factors. Information about the genetic factors in complex disorders can help to predict the probability of future development of disease.
Understanding the issue of probability is important for the ethical use of genetic testing technology. "Genetic determinism" describes the idea that genes hold the map of an individual's future health. Although the detection mutations changes in of some mutations can diagnose the presence of a disease, many other tests DNA sequences provide only information about risk for disease, not a certainty that disease will develop. For example, genetic testing to detect mutations in the gene for breast cancer (BRCA1) can give information about an individual's susceptibility to developing breast and ovarian cancer. However, the probability of developing cancer will depend not only on the status of the gene, but also on factors related to family history and environmental exposures.
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