For the purposes of this section, "dependent" shall mean: A son or daughter of the taxpayer or a descendant of either; a stepson or stepdaughter of the taxpayer; a brother, sister, stepbrother, or stepsister of the taxpayer; the father or mother of the taxpayer or an ancestor of either; a stepfather or stepmother of the taxpayer; a son or daughter of a brother or sister of the taxpayer; a brother or sister of the father or mother of the taxpayer; a son-in-law, daughter-in-law, father-in-law, mother-in-law, brother-in-law, or sister-in-law of the taxpayer. As used in this paragraph the terms "brother" and "sister" include a brother or sister by the half blood. For the purpose of determining whether any of the foregoing relationships exist, a legally adopted child of a person shall be considered a child of such a person by blood.
Ala. Code § 40-18-19 (1975)