Question

Carefully observe the given picture. A mixture of DNA with fragments ranging from 200 base pairs to 2500 base pairs was electrophoresed on agarose gel with the following arrangement.

(a) What result will be obtained on staining with ethidium bromide? Explain with reason.

(b) The above setup was modified and a band with 250 base pairs was obtained at X.

What change(s) were made to the previous design to obtain a band at X? Why did the band appear at position X?

Answer 1

(a) No bands will be obtained as all DNA will be seen in the well only; DNA fragments being negatively charged will not move towards the negative end/cathode. DNA being negatively charged will remain stationed at the positive end/anode end of the agar block.

(b)

1. The position of the positive terminal/end/anode and the negative terminal/end/cathode was inter-changed.
2. The fragment with the least base pairs will get separated faster and move faster to the anode end.