26.20.050 Incest.
(1) A person commits the offense of incest if he or she has sexual contact or sexual intercourse with:
(a) A lineal or collateral ancestor or descendant of the fourth degree of the whole or half blood;
(b) A brother or sister of the whole or half blood;
(c) Any stepson or stepdaughter; or
(d) Adopted son or daughter.
(2) For the purpose of determining the degree of a relationship, it shall be determined by counting “upward” from one of the persons in the sexual relationship, and then “downward” to the other participant, counting one degree for each generation in the ascending as well as descending line.
(3) Consent is a defense under this section to incest with or upon a stepchild, adopted child, or a child that has legal guardian, but consent is ineffective if the victim is less than eighteen (18) years old.
(4) Incest is a Class F offense.