Ala. Code § 13A-13-3: Incest.

(a) A person commits incest if he or she marries or engages in sexual intercourse with a person he or she knows to be, either legitimately or illegitimately, any of the following:

(1) His or her ancestor or descendant by blood or adoption .

(2) His or her brother or sister of the whole or half-blood or by adoption .

(3) His or her stepchild or stepparent, while the marriage creating the relationship exists .

(4) His or her aunt, uncle, nephew or niece of the whole or half-blood.

(b)(1) Incest is a Class C felony.

(2) Where the victim is under 17 years of age on the date of the offense, incest is a Class A felony .