You are given a plasmid that could be one of three different plasmids and asked

Question

You are given a plasmid that could be one of three different plasmids and asked to identify it based on the plasmid maps in the figure below. You perform a couple of RE digest of the plasmid and get the gel shown below. Shown in lane 1 is a series of size (in base pairs) markers. Lane 2 shows the fragments generated by digestion with EcoR I only and Lane 3 shows digestion with both EcoR I and Not I at the same time. Identify your plasmia Plasmid maps for P1-3 Gel of RE Digests EcORI 4800 EcORI 4800 EcoRI 45 EcoRI 500 EcoRI 800 CORI 800 2000 | 1200- 800 P2 5000 P3 5000 Notl 3900 Notl 3 Hindlll 1800 ind? 1800 Hindlll 1800 EcoRI 3 EcORI 3000 EcoRI 3000

Explanation / Answer

for plasmid P1 - double digestion with Eco R1 and Not 1 we will get 4 fragments-

1000 bp, 2500 bp, 900 bp and 600 bp. = 5000 bp.

digestion with eco R1will give us 3 fragments-

2500 bp, 1000 bp and 1500 bp.

for plasmid P2 - double digestion with Eco R1 and Not 1 we will get 4 fragments-

1000 bp, 2200 bp, 900 bp and 900 bp. = 5000 bp.

digestion with eco R1will give us 3 fragments-

2200 bp, 1000 bp and 1800 bp.

for plasmid P3 - we do not find any RE site of Not 1 so single digestion with Eco R1 or double digestion with EcoR1 and Not 1 will give us the same digestion pattern in a gel. so we will get 3 fragments -

2200 bp, 1000 bp and 1800 bp.

Now by looking the gel-

In lane 2 we got 3 fragments after digestion with EcoR1 of length- 1000 bp, 1800 bp (because the band is slighty lower than the marker's 2000 bp fragment) and 2200 bp.

and in lane 3 after double digestion we got 3 fragments of length - 900 bp, 1000 bp and 2200 bp. also we see that the 900 bp band is thick as compared to the other bands which indicate that we might get 2 bands of 900 bp.

so by comparing this gel with plasmids we conclude that our plasmid is PLASMID 2 .

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