Read through and complete the necessary sections. Once you have completed the case study, you will turn in the tables and questions answered in complete sentences.

USING BLOOD TESTS TO IDENTIFY BABIES AND CRIMINALS

Copyright, 2012, by Drs. Jennifer Doherty and Ingrid Waldron, Department of Biology, University of Pennsylvania

WERE THE BABIES SWITCHED?

Two couples had babies in the same hospital at the same time. Michael and Danielle had twins, a boy, Michael, Jr., and a girl, Michelle. Denise and Earnest had a girl, Tonja. Danielle was convinced that there had been a mix-up and she had the wrong girl, since Michael Jr. and Tonja were both light-skinned, while Michelle had darker skin. Danielle insisted on blood type tests for both families to check whether there had been a mix-up. In order to interpret the results of the blood type tests, you will need to understand the basic biology of blood types.

Genetics of Blood Types
Your blood type was established before you were born, by genes inherited from your mother and father. This blood type gene has three different versions, or alleles, that code for different versions of a protein enzyme as follows:

The IA allele codes for a version of the enzyme that puts Type A carbohydrate molecules on the red blood cells.
The IB allele codes for a version of the enzyme that puts Type B carbohydrate molecules on the red blood cells.
The i allele codes for an inactive version of the enzyme, so red blood cells have neither type of carbohydrate molecule on their surface.

Everyone has two copies of these genes, one allele from their mother and one allele from their father. There are six possible combinations of allele a person can have.

IA IA = Blood Type A
IA i = Blood Type A
IB IB = Blood Type B
IB i = Blood Type B
IA IB = Blood Type AB

i i = Blood Type O

Were the babies switched?

Now you are ready to evaluate whether Earnest and Denise’s baby girl was switched with Michael and Danielle’s baby girl. The following family trees show the blood types for each person in both families:

Using the blood types of the parents, make a table to identify the possible blood types for Michael Jr, Michelle and Tonja.

Is it possible for Michael and Danielle to have a child who has type O blood? How do you know this?

Was a switch made at the hospital? Explain your reasoning.

How could fraternal twins be as different in appearance as Michelle and Michael, Jr., including one having light skin and the other having dark skin?