The sons of Reuben the first-born - As Reuben was the eldest son of Jacob, why was not his genealogy reviewed first? This verse answers the question; he lost the birth-right because of the transgression mentioned Genesis 35:22; Genesis 49:4, and the precedency was given to Judah; from him therefore came the chief ruler. This appears to be the meaning of the place.
His birthright was given - In particular, the right of the first-born to a double inheritance Deuteronomy 21:17 was conferred on Joseph, both by the expressed will of Jacob Genesis 48:22 and in the actual partition of Canaan Micah 5:2.