The exchange operator filed a proposal with the SEC on Tuesday that would require listed companies to have at least one woman on their boards, in addition to a director who is a racial minority or one who self-identifies as lesbian, gay, bisexual, transgender or queer. Companies that don’t meet the standard would be required to justify their decision to remain listed on Nasdaq. In a review carried out over the past six months, Nasdaq found that more than three-quarters of its listed companies would have fallen short of the proposed requirements.