Mark 10:7 is quoted from Genesis 2:24 in the Septuagint (the “LXX”). The Hebrew text differs slightly from the LXX. This occurs again in Ephesians 5:31. Matthew 19:5 is similar, but uses a different word for “joined.”
“be joined to.” The Greek is proskollaō (#4347 προσκολλάω), and it literally means to glue to. See commentary on Ephesians 5:31, which uses the same Greek word and quotes the same Old Testament verse.