Practice question

MCQ

Question

A study is done on a mammalian cell line that has a doubling time of 24 hours. These cells are synchronized in G1 and then labeled for 2 days with BrdU (an analog of thymidine). At the end of labeling period, chromosomal DNA is isolated from the cells and its density analyzed by equilibrium centrifugation in cesium chloride gradients. Which of the following patterns would be expected to be seen? (H = heavy, L = light)

Options

Choose one · Correct answer highlighted

100% H/H 100% H/L 50% H/H, 50% H/L Correct 50% H/H, 50% L/L

Explanation

Cells in G1 labeled continuously with BrdU incorporate heavy thymidine analog into new DNA. After one doubling all duplexes are H/L. After second doubling, H/L chromatids produce 50% H/L and 50% H/H upon semiconservative replication, yielding mixed density pattern.

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