26 CFR § 1.151-2 - Additional exemptions for dependents.
(a) Section 151(e) allows to a taxpayer an exemption for each dependent (as defined in section 152) whose gross income (as defined in section 61) for the calendar year in which the taxable year of the taxpayer begins is less than the amount provided in section 151(e)(1)(A) applicable to the taxable year of the taxpayer, or who is a child of the taxpayer and who -
(b) The only exemption allowed for a dependent of the taxpayer is that provided by section 151(e). The exemptions provided by section 151(c) (old-age exemptions) and section 151(d) (exemptions for the blind) are allowed only for the taxpayer or his spouse. For example, where a taxpayer provides the entire support for his father who meets all the requirements of a dependent, he is entitled to only one exemption for his father (section 151(e)), even though his father is over the age of 65.