How I teach - Investigate how blood is true to type
Genetics is perhaps one of the most interesting biology units for students. They are fascinated to learn how microscopic DNA molecules contain all the information for a human being to develop and function.
However, one problem in teaching genetics is finding interesting, hands-on activities, which are plentiful in other areas such as chemistry and anatomy. Students can extract DNA from a piece of onion or their own saliva. They can observe their own dimples, earlobes and other visible traits. But then what?
We tend to think of visible genetic traits such as eye and hair colour, but many cannot be seen by the naked eye. One of these traits is our blood type, which can be a great topic to bring into the school science lab.
Although many people do not know their own blood type, students may have donated blood or know someone who has. And they probably realise that if they were ever to need a transfusion, they would only be able to receive a type of blood that was compatible with their own.
It's also common knowledge that our blood type is inherited and doesn't change. Those who have watched old detective shows from before DNA testing was in use may remember blood typing being used as a way to narrow down the pool of suspects after a crime.
So how is blood type determined? It's actually a fairly simple process. Testing a sample of blood identifies proteins known as antigens on the red blood cells. The three antigens a blood typing test can detect are A, B and Rh. Every person has one, two, all or none of the antigens, and the combination determines their blood type.
The antigens are detected by adding chemicals called antibodies to the blood sample. The A antibody will react with the A antigen on the red blood cells, causing the cells to agglutinate, or clump together. This will lead to a noticeable change in the appearance of the blood, thereby showing that A is part of that person's blood type.
The B and Rh antibodies are also added to separate samples of the blood. The blood type is determined by which of the three antibodies react. For instance, if only the A antibodies react, the person's blood type is A-. If all three antibodies react, the blood type is AB+. If none of the antibodies react, the blood type is O-.
No needles required
How can we get our students doing this visual genetic testing? The most realistic way would be to do an actual blood test, but for obvious reasons this would be impractical. Many teachers use a simulated blood testing kit that can be purchased from a science supply catalogue. However, I have found these kits to be prohibitively expensive and not especially good.
Instead, I've created my own simulated blood typing test. It's much cheaper and equally effective, and it can be made with three easy-to-purchase chemicals: calcium chloride, sodium silicate solution and red food colouring. With these and some dropper bottles, any science teacher can make the simulation kit: I've shared the instructions on the TES website (see bit.lyBloodTestingKit). While genetics is a fascinating subject to teach and study, it can be difficult to engage students in hands-on experiments. A blood type simulation test can be an interesting, fun and cheap way to demonstrate how genetics is used in a real-life application. Seth Robey is a high school teacher in Chicago, Illinois, in the US
While genetics is a fascinating subject to teach and study, it can be difficult to engage students in hands-on experiments. A blood type simulation test can be an interesting, fun and cheap way to demonstrate how genetics is used in a real-life application.
Seth Robey is a high school teacher in Chicago, Illinois, in the US