JACKSON, Miss.—Mississippians are voting on a measure that could prompt a new national fight over abortion by declaring that life begins at fertilization.

It's one of three state constitutional amendments on the ballot Tuesday. Voters will also pick a governor to succeed term-limited Republican Gov. Haley Barbour.

The initiative to define life is an effort by the so-called personhood movement, which wants to put similar measures on other state ballots in 2012.

If approved, supporters say it could prompt a court challenge seeking to overturn Roe v. Wade, the 1973 U.S. Supreme Court decision that established a legal right to abortion.

The initiative is endorsed by both candidates in the governor's race, Republican Phil Bryant and Democrat Johnny Dupree.

Another ballot initiative would require voters to show government-issued identification.

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