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Were the babies switched? – The Genetics of Blood Types and Skin Color

3 babies with different skin color

In this minds-on, hands-on activity, students learn about the genetics of ABO blood types, including multiple alleles of a single gene and codominance. Then, students use chemicals to simulate blood type tests and carry out genetic analyses to determine whether hospital staff accidentally switched two babies born on the same day.

Next, students analyze the genetics of skin color in order to understand how fraternal twins can have different skin colors. In this analysis, students learn about incomplete dominance and how a single phenotypic characteristic can be influenced by multiple genes and the environment. (NGSS)

Download Student Handout: PDF format or Word format

Download Teacher Preparation Notes: PDF format or Word format

The Teacher Preparation Notes provide instructional suggestions and background information and explain how this activity is aligned with the Next Generation Science Standards (NGSS). We invite comments on this activity. If you would prefer to send your comments or questions in a private message, please write Ingrid Waldron at


iwaldron's picture

2024 revision

The revisions of the Student Handout should increase student engagement and understanding. I have also revised the Teacher Preparation Notes and added recent research results.


iwaldron's picture

2022 revision

I have clarified and streamlined the previous genetics version of the Student Handout. One important clarification has been to provide more scaffolding for the student analysis and interpretation of the experimental results. The Teacher Preparation Notes provide an optional supplement to the Student Handout that includes additional information and questions about immunobiology. I have clarified the information in the Teacher Preparation Notes, with special attention to clarifying the instructions for preparing the materials for the hands-on experiment.


Matthew Brown's picture

Where to buy blood

I don't understand whether I can buy the supplies for this lab or not... I presume there is some kind of kit available with (simulated) blood and testing substances to yield the required results?

iwaldron's picture


Please see pages 4-5 of the  Teacher Preparation Notes for information about where to buy a kit or how to make your own supplies. Pages 3-4 of the Teacher Preparation Notes provide additional helpful information.

Danielle Cohn's picture


How can one go about obtaining a key for this particular lab? Brilliant work by the way.

iwaldron's picture


Please see the Teacher Preparation Notes for instructional suggestions, background biology and information about how to get the key.

Ingrid Waldron

Isabelle G's picture


I am homeschooling my child and this is a perfect lab to use! But I unfortunately dont have the Key, Would you be able to send it through my email?

iwaldron's picture

Home schooling Parents

We are happy that many homeschoolers and their parents have found our activities useful. Unfortunately, we cannot supply keys for our activities to homeschooling parents. Please use the information in the Student Handout and Teacher Notes, plus the information that can be found in a good high school or college textbook, to figure out the answers.

With best wishes for success in your science learning,
Ingrid Waldron

Qetsiyah Yisrael's picture

Using Blood test to identify babies worksheet

could we get the answer key

Serendip Visitor's picture

Were the Babies Switched?

I also would be pleased to receive the answer key to this workseet.
Thank you.
John Wakefield.

iwaldron's picture


Please see the Teacher Preparation Notes which provide learning goals, explanations, background information, instructional suggestions, and information about how to request a key.


Serendip Visitor's picture

key to switched?

I love this activity and my students did too! If I could get the key, I would be most appreciative.

Visitor's picture

Were the babies switched - key

Please send me a key for this worksheet.

iwaldron's picture

Answer key

Please see the Teacher Preparation Notes which provide learning goals, explanations, background information, instructional suggestions, and information about how to request a key.


Kathleen's picture

Blood Type Activity

My students loved this activity. It was their favorite assignment of the year. Thank you!

iwaldron's picture

2017 revision

The questions in the Student Handout have been revised to enhance student understanding and learning. In addition, I developed two versions of the Student Handout – one that includes analysis of the immunobiology and one with very little immunobiology and instead a section on the genetics of skin color that introduces concepts such as incomplete dominance and polygenic inheritance. The Teacher Preparation Notes provide improved instructions for the supplies and experiment.

Lisa Brake's picture

Blood Typing Activity

I am having a hard time following this activity - do you have a key by chance?

iwaldron's picture

Resources for Teachers

Please see the Teacher Preparation Notes which provide learning goals, explanations, background information, instructional suggestions, and information about how to request a key.


Serendip Visitor's picture

Were the babies switched

I could not open the Word Doc for the student edition of this lesson. I love the lesson and wanted to print the newer version as a word doc. Thank you.

Ann Dixon's picture

Link to student handout is fixed

Thanks for letting us know!


iwaldron's picture

2016 Revision

This activity has a new name, which reflects a major revision to align the activity with NGSS standards and focus the activity on understanding genetics and the biology of blood types.

Nicole N's picture


How long does the lab take? Has anyone done it to know how many minutes is required (class periods)?

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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