E17 - E1 Due to semiconservative DNA replication one of the...

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E1. Due to semiconservative DNA replication, one of the sister chromatids has both of the DNA strands that contain BrdU while the other sister chromatid only has one of its two DNA strands that contain BrdU. E2. You would conclude that the substance is a mutagen. Substances that damage DNA tend to increase the level of genetic exchange such as sister chromatid exchange. E3. You would add it after the second round of DNA replication but before crossing over occurs during mitosis (i.e., add it during the G 2 phase). In this experiment you are detecting SCEs that occur after the second round of DNA replication. If the mutagen can persist in the cells a long time, you might be able to add it earlier. E4. The drawing here shows the progression through three rounds of BrdU exposure. After one round, all of the chromosomes would be dark. After two rounds, all of the chromosomes would be harlequin. After three rounds, the number of light sister chromatids would be twice as much as the number of light sister chromatids found after two rounds of replication. E5. BrdU inhibits Giemsa binding. As described in Chapter 8, the binding of Giemsa to chromosomes produces G bands, which are dark. The chromatids that contain both strands of BrdU are light, indicating that BrdU inhibits Giemsa binding. E6. When McClintock started with a colorless strain containing Ds, she identified 20 cases where Ds had moved to a new location to produce red kernels. This identification was possible because the 20 strains had a higher frequency of chromosomal breaks at a specific site, and because of the mutability of particular genes. She also had found a
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E17 - E1 Due to semiconservative DNA replication one of the...

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