Thursday, May 16, 2013

On Teaching Genetics Using Students' and Parents' ABO Blood Types

There are some schools that think it's cool to show examples of simple Mendelian inheritance by collecting and analyzing the blood types of their students and their parents. What could possibly go wrong?

Let me tell you why this is a bad idea. It's true that 99% of the time the blood type of a student is going to be consistent with that of their presumed biological parents. But what if it's not? That could mean that a child is adopted and the child may not know or not want that information to be public. It could also mean that the child's biological father (or mother) is not the same person they call "Mommy" or "Daddy." Is the trauma associated with that discovery worth the benefits of the experiment?

I have a blog post on The Genetics of ABO Blood Types. It's quite popular and every few weeks I get a letter from a distraught parent who has just discovered that the blood type of their children doesn't match the blood type of the parents. Here's the latest example (posted with permission) ...
Dear Professor Moran: I hope you don't mind my writing to you, but I just came across your blog, Sandwalk after doing some research about blood types and wondered if you might have an opinion....

My daughter, in 7th grade is working on a blood type project at school and came home quite upset yesterday after telling the teacher that she was type A+ and both her Dad and I are O+. The teacher (whom I have not yet dragged over hot, burning coals....) told her that that was impossible - that she would either have to have been adopted or have a genetic defect.... It got me thinking that perhaps I had made a mistake somewhere along the way and we spent some time last night digging through info to try to figure it out. I checked with our doctors this morning and our daughter's pediatrician and all blood types have been confirmed. Both my husband and I are O+ and our daughter is A+ She is definitely not adopted and unless she was switched at birth, then there is no doubt as to parentage -- should I be concerned? I do recall that when she was born she had mild jaundice which one doc explained was due to blood type incompatibility.
If high school teachers aren't knowledgeable enough to handle these situations then they should avoid these "experiments."

These "anomalies" are quite frequent and they have simple explanations once you know the real genotype. For example, one parent could be heterozygous for two different O alleles. One with a mutation near the beginning of the gene and the other with a mutation near the end of the gene. Any germ cell recombination event between the two alleles could generate an A allele or a B allele depending on the origin of the O allele.

I think it's also possible for one of the parents to actually be AO or BO but the functional allele is expressed at a very low level giving an O-type phenotype. The A or B allele could, by chance, be much more active in the child. There could be epistatic effects such that splicing or transcription is defective in the parent but compensated for by enhanced activity in the child due to unlinked mutations. (These are known as "suppressors" in bacterial genetics.)

There are many other possibilities. They're rare but it's certain that they will show up in some school class somewhere. It's usually not a good idea to investigate the personal genomics of students because of these problems.


10 comments :

  1. I agree. In the US, if what the students are doing is "research", rather than for example a clinical study, they will require signed informed consent forms from all participants approved by an IRB with the risks of the study clearly delineated.

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  2. I know that where I teach we are not permitted to take blood samples from students. We are not trained to take blood, nor do we work in a sterile environment. Whenever I teach ABO blood type crosses, I usually work with hypothetical situations, so we dont get into anything too personal.

    But, I will be honest, this is the first I have read of different O alleles. I've always read, and understood the O allele to be an absence of A and B alleles. Looks like I have something new for my lessons.

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  3. My blood type is AB-. I don't remember what my parents' blood types are.

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    1. EDIT

      This stuff also happens when speaking about eye color heredity, even in college basic genetics courses. Suddenly, a junior student will come up and say "but professor, my parents both have shinny blue eyes and I have dark brown eyes. What's up with that?" and everyone is like "ups...."

      I've read a post here at Sandwalk about eye color genetics and clearly it's a bit more complicated than the simplistic mendelian way eyes color genetics is usually used as an example even in college.

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    2. My college genetics professor told a similar story 50 years ago to tip students to the risk of embarrassment when using personal traits to question Mendelian genetics.

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  5. One of my colleagues was doing genetic research that involved collecting samples from entire families. One unexpected incidental finding was that, while for first children the paternity of the identified father was a most always confirmed, for a second child it went down to around 50%, and below that for subsequent children. Wisely, the investigators did not inform subjects of this. But if you were born late in a large family, you might want to have a look around the table at the next family gathering and consider how much you really resemble those people....

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    1. This should not be a surprise to most parents actually. Once you have a child, finding a 'quiet moment' to make another is hard. Once you have two children, it's even harder!!

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    2. Unless those numbers refer to a specific culture, I'm pretty sure that a 50% or higher cuckoldry rate is unheard of. I suspect that you have not remembered the values correctly.

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  6. I was told that the university where I studied did some kind of chromosome prep practical with the students' own chromosomes until they had a few cases where previously unknown aneuploidies and suchlike were inadvertently discovered during the course.

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