Question 1 (1 point) Consider the experiment described in Lecture 2.1 starting on slide 58 ("Meselson and Stahl Experiment'). Suppose that, after 1 generation, Meselson and Stahl had observed a single DNA band migrating exactly in between the N^14 and N^15 positions (red on the lecture slides). Further suppose that after two generations, they observed one band at the N14 position (orange)and one band at the N15 position (dark red / maroon). This result would be consistent with which model of DNA replication? None of the three models presented in class Dispersive Conservative Semi -conservative

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Question 1 (1 point) Consider the experiment described in Lecture 2.1 starting on slide 58 ("Meselson and Stahl Experiment'). Suppose that, after 1 generation, Meselson and Stahl had observed a single DNA band migrating exactly in between the N^14 and N^15 positions (red on the lecture slides). Further suppose that after two generations, they observed one band at the N14 position (orange)and one band at the N15 position (dark red / maroon). This result would be consistent with which model of DNA replication? None of the three models presented in class Dispersive Conservative Semi -conservative

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**Conservative**The described results perfectly match the predictions of the conservative model. Let's break down why:* **Generation 1:** A single band between N14 and N15 indicates that all DNA molecules are of intermediate density. This happens in the conservative model because the original N15 DNA is fully conserved, and an entirely new N14 DNA molecule is created.* **Generation 2:** Two distinct bands, one at N14 and one at N15, further support the conservative model. This is because the original N15 DNA continues to replicate conservatively, producing another N15 copy. The N14 DNA from the first generation also replicates, creating more N14 DNA. This results in a population with equal amounts of N14 and N15 DNA, hence the two distinct bands.Why the other models don't fit:* **Semi-conservative:** Semi-conservative replication would produce a single intermediate band in generation 1 (as observed). However, in generation 2, it would yield two bands: one intermediate band and one N14 band. There would be no N15 band.* **Dispersive:** Dispersive replication would also produce a single intermediate band in generation 1. However, in generation 2, it would result in a *single* band, slightly closer to the N14 position than the intermediate band from generation 1 (as the proportion of N14 increases with each replication). Two distinct bands would not be observed.

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