Thy issue, which thou begettest after them. — We gather from Genesis 1:23 that Joseph probably had no other sons. But if such were born to him, they were not to count as heads of tribes, but be regarded as the children of Ephraim and Manasseh, and take rank only as heads of families.
Related Commentaries of Genesis 48:6
Genesis 48:6
6 And thy issue, which thou begettest after them, shall be thine, and shall be called after the name of their brethren in their inheritance.