Introduction to Genetic Analysis 473

Introduction to Genetic Analysis 473 - 44200_14_p451-480...

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Repair of double-strand breaks As we have seen, DNA complementarity is an important resource that is exploited by many error-free correction systems. Such error-free repair is characterized by two stages: (1) removal of damaged and nearby DNA from one strand of the double helix and (2) use of the other strand as a template for the DNA synthesis needed to Fll the single-strand gap. However, what would happen if both strands of the double helix were damaged in such a way that complementarity could not be exploited? One way this might happen is if both strands of the double helix were to break at sites that were close together. A mutation like this is called a double-strand break. If left unrepaired, double-strand breaks can cause a variety of chromosomal aberrations resulting in cell death or a precancerous state. Interestingly, the ability of double-strand breaks to ini- tiate chromosomal instability is an integral feature of some normal cellular processes that require DNA rearrange- ments. One example is the generation of the diversity of antibodies in the cells of the mammalian immune system.
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