These were the sons of Reuben the firstborn of Israel. Though he was the firstborn, his birthright was given to the sons of Joseph son of Israel, because Reuben defiled his father’s bed. So he is not reckoned according to birthright.
KJV
Now the sons of Reuben the firstborn of Israel, (for he [was] the firstborn; but, forasmuch as he defiled his father’s bed, his birthright was given unto the sons of Joseph the son of Israel: and the genealogy is not to be reckoned after the birthright.
ASV
And the sons of Reuben the first-born of Israel (for he was the first-born; but, forasmuch as he defiled his father’s couch, his birthright was given unto the sons of Joseph the son of Israel; and the genealogy is not to be reckoned after the birthright.