Scientists discovered that the difference between blond and dark hair comes down in part to a single nucleotide difference in the DNA sequence of an enhancer that lies more than 350,000 base pairs away from the gene it controls. On average, blonds transcribe this gene less efficiently than people with dark hair. How can a tiny difference in a distant enhancer make a blond?

The answer is given below.

Explanation:

A tiny difference in a distant enhancer make a blond through DNA Looping.

DNA Looping can bring the enhancer bound by an activator physically closer to the promoter even if the enhancer is located far away along the DNA molecule.

DNA Looping.

When a protein or a set of complex proteins binds to 2 different sites of DNA simultaneously while looping out the interfering DNA.  

Important of DNA Looping