1. Suppose I repeat the Meselson-Stahl experiment, but I make a mistake. Instead

Question

1. Suppose I repeat the Meselson-Stahl experiment, but I make a mistake. Instead of growing the cells in (_^15)N 15N and switching to 14N, I grow my bacteria in 14N and then switch to 15N. If DNA replicates using a dispersive mechanism, what will I see after two rounds of replication?

A) There will be a single heavy band in the tube.

B) There will be a single light band in the tube.

C) There will be a single light band in the tube.

D) There will be a single band between half-heavy and heavy in the tube.

E) There will be a light band and a heavy band in the tube.

F)There will be a half-heavy band and a heavy band in the tube.

2. This question refers to the situation described in question above , If DNA replicates using a conservative mechanism, what will I see after two rounds of replication?

A) There will be a single heavy band in the tube.

B) There will be a single light band in the tube.

C)There will be a light band and a heavy band in the tube.

D) There will be a single band between half-heavy and heavy in the tube.

E) There will be a half-heavy band and a heavy band in the tube.

F) There will be a single half-heavy band in the tube.

Explanation / Answer

Dispersive replication. In the dispersive model, DNA replication results in two DNA molecules that are mixtures, or “hybrids,” of parental and daughter DNA. In this model, each individual strand is a patchwork of original and new DNA.

Therefore

1. E) There will be a light band and a heavy band in the tube.

Conservative replication. In this model, DNA replication results in one molecule that consists of both original DNA strands (identical to the original DNA molecule) and another molecule that consists of two new strands (with exactly the same sequences as the original molecule).

Therefore

2. C) There will be a light band and a heavy band in the tube.

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