Question

An actor who is the great-aunt of her half-sister's grandchild shares what coefficient of relatedness with that child?

1) 1/4
2) 0
3) 1/8
4) 1
5) 1/16

Answer 1

The correct coefficient of relatedness between the actor who is a great-aunt and her half-sister's grandchild is 1/8, as the genetic relationship is halved at the half-sister generation and then halved again at the parent-child generation.

Step-by-step explanation:

The coefficient of relatedness between an actor who is the great-aunt of her half-sister's grandchild is 1/4. To understand why, consider the following: A great-aunt shares a 1/2 genetic relationship with their sibling (the grandparent), who in turn shares a 1/2 genetic relationship with their child (the parent of the grandchild), who then also shares a 1/2 genetic relationship with their child (the grandchild). The combined relationship is calculated as (1/2) × (1/2) × (1/2) = 1/8. However, because the sibling in this scenario is a half-sister, the initial relationship is 1/4 (instead of 1/2). Therefore, the relationship between the great-aunt and the half-sister's grandchild is (1/4) × (1/2) × (1/2) = 1/16, but since the question indicates that the great-aunt is related to her half-sister's grandchild, there is an additional halving missed in the calculation. It should correctly be (1/4) × (1/2) = 1/8, making the correct option 3) 1/8.