For purposes of this chapter, the generation to which any person (other than the transferor) belongs shall be determined in accordance with the rules set forth in this section.
An individual who is a lineal descendant of a grandparent of the transferor shall be assigned to that generation which results from comparing the number of generations between the grandparent and such individual with the number of generations between the grandparent and the transferor.
An individual who is a lineal descendant of a grandparent of a spouse (or former spouse) of the transferor (other than such spouse) shall be assigned to that generation which results from comparing the number of generations between such grandparent and such individual with the number of generations between such grandparent and such spouse.
This subsection shall not apply with respect to a transfer to any individual who is not a lineal descendant of the transferor (or the transferor’s spouse or former spouse) if, at the time of the transfer, such transferor has any living lineal descendant.
Except as provided in regulations, an individual who, but for this subsection, would be assigned to more than 1 generation shall be assigned to the youngest such generation.
Except as provided in paragraph (3), if an estate, trust, partnership, corporation, or other entity has an interest in property, each individual having a beneficial interest in such entity shall be treated as having an interest in such property and shall be assigned to a generation under the foregoing provisions of this subsection.