The origin of the Escherichia coli chromosome on the genetic map is shown below. Bidirectional replication is a feature of this system and both replication forks move at the same rate. Which one of the following sequences of replication of the genes is correct?
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In bidirectional replication, always remember that the replication forks move in opposite directions from the origin of replication, and genes are replicated in the sequence from the origin outward in both directions.
In Escherichia coli (E. coli), the process of DNA replication starts at the origin of replication, denoted as Ori. Replication in E. coli is bidirectional, meaning that replication proceeds in both directions from the origin. The replication forks move in opposite directions around the circular chromosome, and both forks replicate DNA at the same rate. In the given genetic map, starting from the Ori, replication will proceed first in the direction towards gene A, then move through genes B, G, F, C, and D, in a manner consistent with bidirectional replication. - Option (A): ABCDEFG is not correct because this sequence implies a unidirectional replication, which is not possible with bidirectional replication. - Option (B): AGBFCD is correct because it follows the bidirectional replication pattern starting from the Ori and passing through genes A, G, B, F, C, and D in the correct order. - Option (C): GAFBEC does not follow the correct order of gene replication, and it is inconsistent with the bidirectional replication process. - Option (D): GAFEBCD is also incorrect, as the order of gene replication does not follow the bidirectional pattern and would not be possible with simultaneous fork movement in both directions. Thus, the correct answer is (B) AGBFCD, which correctly represents the sequence of gene replication in a bidirectional manner.
