Pleiotropy occurs when a single gene influences multiple phenotypic traits. Consequently, a new mutation in the gene may have an effect on some or all traits simultaneously. This can become a problem when selection on one trait favors one specific version of the gene (allele), while the selection on the other trait favors another allele. Etymology The term pleiotropy comes from the Greek πλείων pleion, meaning "more", and τρέπειν… (More on Pleiotropy)