Genesis - Chapter 38

Having started on the story of Joseph in Chapter 37, there is a short break while we read about Judah.  Judah marries, and has a son who marries Tamar.  The son dies, and Judah's family do not properly care for the widow Tamar.  Tamar's response is to pretend to be a prostitute, and Judah (not knowing it is Tamar) sleeps with her and gets her pregnant.  

She gives birth to twins, the elder or whom is Perez.

These are the people who appear in Jesus' family tree in Matthew Chapter 1.

Jacob (was) the father of Judah and his brothers; Judah the father of Perez and Zerah whose mother was Tamar; Perez the father of Hezron; and so on.

Not only was Jesus descended from Judah and Perez, but Tamar is one of the few women to be mentioned in Jesus' family tree.