When you are unable to date/hookup/start relationships with someone so you resort to doing what was intended with them with their siblings or cousins instead.
“Yo, sucks that Ella won’t date you”
“That’s fine bro, I can always date her sister Carrie”
“You be pulling one of them same DNA same P in A’s!
“Same DNA, same P in A!”
Dating someone's sibling because you cannot date them for various reasons
"Bro, you can't date Sarah"
"That's fine, I'll just date her sister"
"Same DNA, same P in A! Next best thing!"