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| Modern Genetic Analysis Chapter 3. Gene Function Introduction Cystic fibrosis is a human disease caused by a defective allele of a single gene. This disease is so severe that in the past it routinely killed children in infancy. The symptoms affect many different parts of the body (Figure 3-1). One prominent symptom is an excessively salty sweat, but the most frequent cause of death is blockage of the airway by an unusually sticky type of mucus. How is it possible that a defect in only one of the 100,000 genes in the human genome can result in death? Obviously the gene provides a crucial function for maintenance of human life. Indeed gene function is a key to understanding this hereditary disease and the thousands of other diseases that can cause human ill health and premature death. In this chapter we shall consider the mechanisms of gene function in organisms generally, and then return to cystic fibrosis to examine the gene involved, its normal function, and what we currently understand about the ways in which the defective allele causes the multiple symptoms.

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