In Judaism, Jacob's sons are Abraham's children, & Abraham's own body continued on, as not only did Judaism teach that flesh & blood are carried on to the next generation, through Abraham's male & female descendants, but also lineage, thru the male blood, which was believed to contain a part of the soul of the Father, as it was believe that one's soul resides in one's blood. 

This is why our church gets these symbolisms in the Gospels very confused.  Jacob-aka Israel, only has any right to anything, in the world, over any other race due to the promises made to Abraham alone.  Only Abraham & Sarah were made the promise that their ancestors would inherit the earth & prosper under God's care & spawn the savior of the world.  If Jacob were to stray, God could have turned to Esau to build the line of the Messiah. 

Jesus has his mother's flesh & blood (Abraham's) but his father's lineage (God's). This makes the Apostles necessary-God promised the Jews to be judged by Abraham's lineage/kin.