In collateral lines, which of the following is a 2nd-degree relationship?

• A. Brother and sister
• B. Uncle and niece
• C. First cousins
• D. Grandparent and grandchild

Answer: (A)

In collateral kinship, the degree is determined by how many generations you must go up to reach a common ancestor, counting only non-direct line relationships. Brothers and sisters share a parent, and each is one generation away from that parent, so the total distance between them is two generations. That makes them a second-degree relationship. Uncle and niece share a grandparent as their closest common ancestor, with distances of one and two generations respectively, totaling three generations—third degree. First cousins share a grandparent as common ancestor as well, but each is two generations from that grandparent, totaling four generations—fourth degree. Grandparent and grandchild are in a direct line, not collateral, so they aren’t counted in the collateral degrees.