Genesis 48:5

48:5 “Now, as for your two sons, who were born to you in the land of Egypt before I came to you in Egypt, they will be mine. ¹  Ephraim and Manasseh will be mine just as Reuben and Simeon are.

Deuteronomy 33:17

33:17 May the firstborn of his bull bring him honor,

and may his horns be those of a wild ox;

with them may he gore all peoples,

all the far reaches of the earth.

They are the ten thousands of Ephraim, ² 

and they are the thousands of Manasseh.

[48:5]  ¹ sn They will be mine. Jacob is here adopting his two grandsons Manasseh and Ephraim as his sons, and so they will have equal share with the other brothers. They will be in the place of Joseph and Levi (who will become a priestly tribe) in the settlement of the land. See I. Mendelsohn, “A Ugaritic Parallel to the Adoption of Ephraim and Manasseh,” IEJ (1959): 180-83.

[33:17]  ² sn Ephraim and Manasseh were the sons of Joseph who became founders of the two tribes into which Joseph’s descendants were split (Gen 48:19-20). Jacob’s blessing granted favored status to Ephraim; this is probably why Ephraim is viewed here as more numerous than Manasseh.