GATE 2020 BT – Question 53

Recombinant DNA Technology and Other Tools in Biotechnology · Recombinant DNA technology: Restriction and modification enzymes, vectors, expression vectors, libraries, gene isolation and cloning, transposons, gene targeting · 2 marks · Numerical answer

A random 1 Mb DNA has equal proportions of all four bases. On average, how many nucleotides separate successive EcoRI recognition sites GAATTC?

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Correct answer: 4096 to 4096

Explanation

For independent equiprobable bases, a specified six-base sequence occurs with probability $(1/4)^6=1/4096$ at a candidate position. The expected spacing between occurrences is therefore the reciprocal, 4096 nucleotides. The large DNA length supplies many candidate positions; it is not multiplied into this spacing.

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