Introduction to Genetic Analysis 459

Introduction to Genetic Analysis 459 - 44200_14_p451-480...

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458 Chapter 14 Mutation, Repair, and Recombination the bromine atom signifcantly alters the distribution oF electrons in the base ring; so 5-BU can frequently change to either the enol Form or an ionized Form; the enol and ionized Forms oF 5-BU pair with guanine (±igure 14-7b). 5-BU causes G · C : A · T or A · T : G · C transi- tions in the course oF replication, depending on whether 5-BU has been enolized or ionized within the DNA molecule or as an incoming base. Hence the action oF 5-BU as a mutagen is due to the Fact that the molecule spends more oF its time in the enol or ion Form. Another widely employed mutagen is 2-amino- purine (2-AP), an analog oF adenine that can pair with thymine (±igure 14-8a). When protonated, 2-AP can mispair with cytosine (±igure 14-8b). ThereFore, when 2-AP is incorporated into DNA by pairing with thymine, it can generate A · T : G · C transitions by mispairing with cytosine in subsequent replications. Or, iF 2-AP is incorporated by mispairing with cytosine, then G·C :
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