​In order to determine the origin of replication of a circular DNA, isolated DNA from the actively replicating cells were digested with different restriction enzymes (as indicated), followed by electrophoresis in a two-dimensional gel. Southern hybridization was performed with a DNA probe as indicated.​

​Based on the results of the Southern blots, indicate which of the following options best describes the location of the origin of replication?​

Correct option is B

EXPLANATION-

Types of Replication Intermediates and Gel Patterns
Double Y (DY)  - Happens when replication starts outside the fragment being probed; the fragment being visualized contains two replication forks.
Bubble arc  - Indicates that replication has initiated within the probed fragment.
Bubble to Y or Bubble arc to Y transition - Indicates a partially overlapping fragment, where replication starts within and exits the probed region.

BamHI Digest (Top Left - Double Y) - Shows a Double Y arc.
Replication forks are entering this fragment from outside, i.e., origin is outside this fragment.

HindIII Digest (Top Right - Bubble to Y) - Shows a Bubble to Y arc.
Replication has started somewhere within this fragment and exits toward one side.

KpnI Digest (Bottom Left - Bubble to Y) -Also shows Bubble to Y.
The origin is within or near this fragment.

EcoRI Digest (Bottom Right - Bubble Arc) - Shows a full Bubble arc.
This fragment contains the origin of replication.

The probe is near EcoRI and BamHI, and NOT near HindIII or KpnI.

However, that BamHI fragment only shows a Double Y, meaning replication forks are moving into this region.
That suggests the origin is just upstream of BamHI — meaning very close to BamHI  — this makes BamHI the closest site to the origin.

So, the correct option is (b)  — Near the BamHI site