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.

Question 27 - Carefully observe the given picture - teachoo.jpg

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

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

Question 27 - What result will be - teachoo.jpg

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



(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 -ive end/ cathode. DNA being negatively charged will remain stationed at the positive end/ anodeend of the agar block;


(a) Position of the positive terminal/ end/ anode and the negative terminal/ end/ cathode was inter-changed

(ii) The fragment with least base pairs will get separated faster and move faster to the anode end.

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.