SOLVED PROBLEM 1. Mitosis and meiosis were presented in Chapter 2. Considering what has been covered in this chapter concerning DNA replication, draw a graph showing DNA content against time in a cell that undergoes mitosis and then meiosis. Assume a diploid cell.

Solution

SOLVED PROBLEM 2. If the GC content of a DNA molecule is 56 percent, what are the percentages of the four bases (A, T, G, and C) in this molecule?

Solution

If the GC content is 56 percent, then, because G = C, the content of G is 28 percent and the content of C is 28 percent. The content of AT is 100 – 56 = 44 percent. Because A = T, the content of A is 22 percent and the content of T is 22 percent.

SOLVED PROBLEM 3. Describe the expected pattern of bands in a CsCl gradient for conservative replication in the Meselson–Stahl experiment. Draw a diagram.

Solution

Refer to Figure 7-13 for an additional explanation. In conservative replication, if bacteria are grown in the presence of ¹⁵N and then shifted to ¹⁴N, one DNA molecule will be all ¹⁵N after the first generation and the other molecule will be all ¹⁴N, resulting in one heavy band and one light band in the gradient. After the second generation, the ¹⁵N DNA will yield one molecule with all ¹⁵N and one molecule with all ¹⁴N, whereas the ¹⁴N DNA will yield only ¹⁴N DNA. Thus, only all ¹⁴N or all ¹⁵N DNA is generated, again yielding a light band and a heavy band: