But a Texas court threw out the lawsuit. Because Christie Lee Littleton was born a man — she had a sex-change operation when she was 27 — the court ruled that the marriage was invalid and that she had no legal ground to sue as a spouse.

Twenty years earlier a court in New Jersey settled a similar case the opposite way: The wife had been born a man but underwent hormone therapy and various surgeries to live as a woman. After she and her husband split up, she sued for spousal support. The husband argued that because his wife was born a man, the marriage wasn’t legal and he owed her nothing. The court ruled that for the purpose of marriage, she was a woman and the husband was forced to pay spousal support.

How courts define gender is garnering attention in legal circles while states consider new laws banning same-sex marriage. In November, Virginia voters will vote on a constitutional amendment defining marriage as “a union between one man and one woman.” But how does the law determine who is a man and who is a woman?

For years, judges across the country have wrestled with the question of how to define gender. Rulings have been inconsistent across the states, but most courts tend to rule in line with the Texas court: Gender is fixed at birth, and sex-change operations, or sex-reassignment surgeries, do not change a person’s legal gender.

So if Texas says someone’s sex cannot change, does that mean Christie Lee Littleton can only marry women? That scenario would look a lot like same-sex marriage.

What would that mean in a state such as Mississippi, where 86 percent of voters supported a gay-marriage ban? And what happens if Littleton, legally a man in Texas, remarries a woman and moves to a state that doesn’t recognize same-sex marriages, but has court precedent that recognizes changes of gender through surgery?

Marriage cases are particularly emotional examples, but such rulings can have broad implications for the legal system.

“There’s huge stuff at stake in these seemingly quirky little cases,” says Anne Coughlin, a gender law specialist at the University of Virginia. “It’s possible that somebody for the purposes of marriage [gets classified] one way, but for the purposes of prison characterized another way.”

Federal law puts prisoners who have had sex changes under the same roof as prisoners of their postoperative sex — a man who becomes a woman through surgery is put into the women’s prison. But transgendered prisoners who haven’t undergone a sex-change operation are placed with people of their natural-born gender — a man living as a woman is put into the men’s prison. Prison isn’t the only place impacted by the legalities of gender.

The LPGA professional women’s golf tour requires participants to be females at birth, but its European counterpart has allowed a Danish transgender golfer to play. Contestants for Miss USA must be natural-born women. Females have two X chromosomes and no Y. Males have one X and one Y. What about people born with Klinefelter syndrome, who have two X chromosomes and one Y chromosome?

Deputy attorney general David Johnson says that as the commonwealth is concerned, sex is defined by what’s on your birth certificate. Virginia state law allows transgender individuals to change the sex designation on their birth certificates if they provide evidence that sexual reassignment surgery has taken place.

So if someone like Christie Lee Littleton gets married in Virginia after undergoing sex-reassignment surgery and changing her birth certificate, on appeal the current office of the attorney general would defend the state’s right to grant the marriage based on what the birth certificate says.

So what if a woman undergoes surgery to become a man, doesn’t change her birth certificate and marries someone who was born a man? Will Attorney General Bob McDonnell, and ardent opponent of same-sex marriage, go to bat for that?

Still, Coughlin says that no case like that has been tried in Virginia, and a court could very well rule that birth certificates are not what determine gender for the purpose of marriage.

“As you can see the questions are messy,” Coughlin says. “Very, very messy.”

Activists on both sides of the debate over Virginia’s constitutional marriage amendment say questions about the meaning of “man” and “woman” have not figured into their campaign strategies for November.

Dyana Mason, executive director of Equality Virginia, says “the mission statement of Equality Virginia is that any person should be able to marry the person of their choosing, but we haven’t thought about it much beyond those terms.”

Supporters of the marriage amendment say the mess Coughlin refers to is a mirage.

“I think we see with this discussion how far homosexual activists are asking everyone else to go even when it comes to defining the most simple terms: man, woman, marriage,” says Victoria Cobb, executive director of the Family Foundation, one of the most vocal proponents of the Virginia marriage amendment. “It’s because they are such basic terms that these scenarios defy nature and logic.”

The Family Foundation gets legal assistance from the Alliance Defense Fund, a national organization committed to banning gay marriage and abortion in the name of religious freedom. Chris Stovall, a senior attorney with the Defense Fund, thinks the importance of protecting marriage as an institution dwarfs the uncertainties concerning how to define “man” and “woman,” and doubts such questions threaten existing statutes or constitutional amendments.

“Marriage as a state matter has never been about love,” Stovall says. “It’s about promoting stable households for the good of the children that are born to women and men preferably living together.”

Stovall says his organization has discussed going after no-fault divorce statutes, but has no immediate plans to do so. All states allow divorces where the spouse suing for divorce does not have to prove that the other spouse did something wrong. So “not getting along” is legal grounds for a no-fault divorce, something ADL would like to see changed.

Even as the list of state statutes and constitutional amendments continues to grow, the U.S. Senate rejected a federal marriage amendment last month by a vote of 49 to 48, leaving the states to determine the boundaries of marriage and gender on their own. S