In addition to deleting a gene of choice, it also is possible to replace the endogenous gene with a mutated form of that gene. As in the strategy for knocking out a gene, DNA constructs that carry mutations in a particular gene can be exchanged for the endogenous gene. It also is possible to replace all of an endogenous gene with a DNA sequence of choice. In a recent report, for example, the CD4 gene was replaced with the one for p-galactosidase. In these experiments, the CD4 promoter was left intact to drive the expression of p-galactosidase, which catalyzes the color change of certain reporter chemicals to blue. Because the CD4 promoter drove the expression of p-galactosidase, only those thymic cells destined to express CD4 turned blue in the presence of the reporter chemicals. Data from these experiments were useful in tracing CD4/CD8 lineage commitment in developing T cells.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.