(a) For purposes of this chapter, a person has a substantial interest in a business entity if:
(1) the person owns 10 percent or more of the voting stock or shares of the business entity or owns either 10 percent or more or $15,000 or more of the fair market value of the business entity; or
(2) funds received by the person from the business entity exceed 10 percent of the person's gross income for the previous year.
(b) A person has a substantial interest in real property if the interest is an equitable or legal ownership with a fair market value of $2,500 or more.
(c) A local public official is considered to have a substantial interest under this section if a person related to the official in the first degree by consanguinity or affinity, as determined under Chapter 573, Government Code, has a substantial interest under this section.