Mo. Rev. Stat. § 568.020: Incest — penalty.

1. A person commits the offense of incest if he or she marries or purports to marry or engages in sexual intercourse or deviate sexual intercourse with a person he or she knows to be, without regard to legitimacy, his or her:

(1) Ancestor or descendant by blood or adoption; or

(2) Stepchild, while the marriage creating that relationship exists; or

(3) Brother or sister of the whole or half-blood; or

(4) Uncle, aunt, nephew or niece of the whole blood.

2. The offense of incest is a class E felony.

3. The court shall not grant probation to a person who has previously been found guilty of an offense under this section.