They found that people with a functional copy of the gene, called OR7D4, made properly shaped

receptors that accepted androstenone. But thirty percent of people had a variation of the gene (OR7D4 WM) that made

a receptor into which the androstenone could not fit. The difference in the receptor was very small Gene l — just

two amino acids differed — but the effects were pronounced. Those with the functional copy were eleven times more

sensitive to androstenone than their counterparts. And that marked the first proof that a particular gene was

responsible for a person's ability to smell a certain odor.
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