|Sts Joachim and Anne presenting little Mary|
in the Temple of the Lord.
Of course, there's a reason for the incompleteness in the family tree. Jesus didn't exactly have paternal grandparents. This is not to disparage the love people can have for their adopted grandchildren; instead, it is a theological statement.
While our grandparents and great-grandparents and their grandparents can be traced, theoretically, in a line stretching back to Eden, Jesus' origin is "from of old, from eternity," and his true Father is the one "from whom every fatherhood in heaven and earth takes its name." As is the case with the Blessed Virgin Mary, everything we say about the grandparents of Jesus reflects what we believe about God.