Medical Genetics 1. Genes can be mutated in many ways The most common gene change nvolves a single base mismatch--a misspelling--placing the wrong base in the dNA. at other times a single base may be dropped or added And sometimes large pieces of DNA are mistakenly repeated or deletedMedical Genetics 1.Genes can be mutated in many ways The most common gene change involves a single base mismatch--a misspelling--placing the wrong base in the DNA. At other times, a single base may be dropped or added. And sometimes large pieces of DNA are mistakenly repeated or deleted