biology a level electrophoresis question

does anyone understand how to work out part ii) and part iii) ? The answers are ii)3 and iii) 2 bands disappear and new band formed at heavier position

Hi!

for part ii: if you imagine having a sequence of DNA that has 3 sites where it will be cut (via the restriction enzyme), there are going to be 4 separate sections of DNA produced. These 4 separate sections are shown in track 1, by the 4 different bands.
Basically, to produce 4 DNA fragments, you need to have 3 sites where a restriction enzyme will work.

for part iii: The genetic condition means that one of the sites where the restriction enzyme would cut is lost, so therefore this site wont be cut. This means that only three fragments will be produced overall, and one of the fagment will be longer than the others, so heavier than the others.

Hope this helps, lmk if u have any more questions about it

Thank you so much that makes so much sense now!