The given gel shows the lanes 1, 2 and 3. Lane 1 shows DNA ladder starting from 100 bp and so on. Lane 2 shows restriction enzyme digestion results of a plasmid containing normal human beta globin allele. Lane 3 shows restriction enzyme digestion of sickle cell anaemia of a plasmid containing diseased allele.

Which of the following is true for the results shown?

The correct option is B Only lane 2 contains a 175-bp fragment

An agarose gel is given in the picture where in lane 1, 100 bp marker has been loaded. So it means, from the bottom the base pair sizes are 100, 200, 300, and so on. In lane 2, there are totally 3 fragments. In that the first fragment (from the bottom) lies between the first two markers of lane 1 (sizes - 100 bp and 200 bp).

Thus, the fragment in lane 2 near to 2nd fragment in lane 1 has a size of 175 bp. Markers are used for this purpose of finding out the base pair size of loaded DNA samples.

Therefore, the correct answer is option B.