Using Blood Tests to Identify Babies and Criminals

In this activity, Using Blood Tests to Identify Babies and Criminals, students learn the genetics and immunobiology of the ABO blood type system and use simple chemicals and logical reasoning to solve a murder mystery and to determine whether two babies were switched in the hospital. This activity introduces students to the concept of codominance; in the Teacher Preparation Notes we suggest an extension which you can use to introduce the concept of incomplete dominance and the difference between codominance vs. incomplete dominance. 

Download Student Handout: PDF format or Word format

Download Teacher Preparation Notes: PDF format or Word format

We invite comments on this Hands-On Activity and the accompanying Teacher Preparation Notes, including suggestions for other teachers who are planning to use the activity, useful preparatory or follow-up activities, additional resources or any questions you have related to the activity, or a brief description of any problem you might have encountered. If you have a relevant Word document you would like to have posted on this comments page, such as a version of the protocol you have used in your classroom, or if you would prefer to send your comments or questions in a private message, please write Ingrid Waldron at

See also a complete list of activities:
Hands-on Activities for Teaching Biology to High School and Middle School Students



iwaldron's picture

2013 revision

The Student Handout has been streamlined and the questions have been revised to focus on the learning goals and more actively engage students in understanding important genetics concepts. The Teacher Preparation Notes have been expanded to clarify the learning goals, provide additional biology background, and suggest alternative approaches that may be useful for your classroom.

iwaldron's picture

August 2012 revision

Some of the questions in the Student Handout have been clarified and the Teacher Preparation Notes have been updated with additional information.

Serendip Visitor's picture

Fake blood

I wonder if there is some way to make your own fake blood that could be coagulated with vinegar? Then it would not be necessary to purchase the blood typing kits.

iwaldron's picture

Cheap fake blood

If you have insufficient budget for the recommended kits, you can make the fake blood samples and anti-sera by adapting the instructions to use food coloring, milk, vinegar and water provided on pages 1-3 of "Teachers’ Talking Science – Blood Typing", available at . However, you should be aware that this cheaper alternative is significantly more complicated for you and your students to use; specifically, you will have to designate different antisera for each sample in order to get the desired results.

Anonymous's picture

freaky out

as you can see im doing my homework right now so i need the answer cuz im lost xD is about identify babies blood and criminals so if u can help me i'llso freaky happy

iwaldron's picture

2010 revisions


We have improved the section on genetics of blood types in the student handout.  The Teacher Preparation Notes now include possible Extension Activities concerning the inheritance of skin color, so students can learn about polygenic inheritance, independent assortment and incomplete dominance (in contrast to co-dominance for the blood type alleles). These extension activities are worksheets, which we have found to be a useful supplement or alternative to hands-on activities for helping students to learn genetics.


iwaldron's picture

A and B antigens actually are carbohydrate molecules

Although the misconception that the A and B antigens are proteins is widespread, it is now well established that this is not true. "The gene that determines ABO ... encodes an enzyme that adds sugar molecules to lipids on the surface of red blood cells. ... The gene that encodes the enzyme, designated I, has three common alleles: IB whose product adds a lactose; IA whose product adds galactoseamine; and i which codes for a protein that does not add a sugar.... If a type A individual receives a transfusion of type B blood, the recipient's immune system recognizes that the type B blood cells possess a "foreign" antigen (galactose) and attacks that donated blood cells, causing them to clump, or agglutinate." (quoted from Raven et al., Biology, seventh edition, page 260).  Additional supporting information can be found in immunology textbooks.

Karen Richard's picture

I would use this blood type

I would use this blood type activity except that the person who typed out the the directions has written that the A and B antigens are "carbohydrate molecules" on the surface of teh RBC. The A and B antigens are PROTEINS.

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