Having become an expert on gel electrophoresis, you are asked to examine a gel for a colleague. Where would you find the smallest segments of DNA ?

Near the positive electrode, farthest away from the wells

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Near the negative electrode, close to the wells

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Near the top, near the negative pole

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Near the middle, they tend to slowdown after the first few minutes

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Solution

The correct option is A Near the positive electrode, farthest away from the wells
DNA is a negatively charged molecule and therefore would move towards the positive end of the gel. But the movement of though the gel is determined by the size of the DNA molecule. The DNA fragments are loaded in a well near to the negative end of the gel. Once the electric field is applied, the DNA fragments start to move towards the positive end. The smallest DNA fragments would move quicker than their larger counterparts and hence be nearest to the positive end of the gel and farthest from the wells.

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