Human Genetics Problem Set

Problem 19: Who is NOT the father of my grandson?

The following is an edited version of an email exchange that occurred in response to the human gentetics tutorial at the Biology Project:

First Message from a concerned grandmother:

I am wondering how to find out blood type of my grandson...my daughter is A+..father is in question...she is stressed to the max on the father of this baby boy.

What is the most common blood type and the most common donor and common receiver?

Answer to First Message by Professor Hallick:

Blood type analysis can occasionally rule out a potential father (i.e. if the mother is type A and the child is type O, the father could not be type AB, but could be type A, B, or O), but is not a method that can be used to establish paternity.
If the paternity of your grandson needs to be established for legal reasons, such as establishing responsibility for child support, a DNA test would be the accepted method. There are commercial laboratories that will do the test for a fee (several hundred dollars). Blood samples would be required from the mother, child, and any alleged fathers.

Second Message from grandmother:

Thanks so much for your prompt reply. Here is the scenario....paternity isn't going to be established...it is going to lay...for lack of a better expression. My daughter is type A, my grandson is type B+, we do not know the types of the two gentlemen in question...my question is what are the types that the fathers would have to be in order for him to be a B+?

What is the correct answer to the grandmother's question, "What are the types that the fathers would have to be in order for him (grandson) to be a B+?"

A. B or O

B. A, B, AB or O

C. AB or B

D. A or B

E. A, B, or AB

The Biology Project
University of Arizona
Revised: November 5, 1998
Contact the Development Team