Sec. 3. (a) A person eighteen (18) years of age or older who engages in sexual intercourse or other sexual conduct (as defined in IC 35-31.5-2-221.5) with another person, when the person knows that the other person is related to the person biologically as a parent, child, grandparent, grandchild, sibling, aunt, uncle, niece, or nephew, commits incest, a Level 5 felony. However, the offense is a Level 4 felony if the other person is less than sixteen (16) years of age.
(b) It is a defense that the accused person's otherwise incestuous relation with the other person was based on their marriage, if the marriage was valid where it was entered into.