Teacher Version


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Blood Type Activity:  Exploring the relationship among three alleles.

GenScope File: BloodType.gs

When this file is opened, a pedigree of three families appears. There are four blood types, A, B, AB, and O. A and B are incompletely dominant to each other and both are dominant to O.

If there is a need to reconstruct this pedigree, the blood types are as follows: Janis AO, John AB, Bob AO, Howie O, Ron A_, Trish BO, Melanie BO, Len AB, Harry O, Stacie B_, Claire BO, James B_, Jill A_.

1.       Trish is Type B and her son, Len, is type AB. What is Ron's blood type?

Ron is A_.

Since one of their children is AB and Trish is B, Ron has to contribute an A gene. The other gene is unknown and unimportant in this context. It could be A, B or O. You can't figure it out from the information given here.

How do you know?

The student should answer that the A gene that Len has (Type AB) had to come from somewhere and Trish doesn't have it. She's type B.

This is a good example of backward reasoning. Since the son has type AB and Trish contributed her B gene to her son, the A gene has to come from the father. But everyone has two genes for blood type. We have no information about what the other gene is. He could be AA, AO or AB. It doesn't matter here.

2.       Is it possible for Janis and John to have a child who is type O?


How can you explain this?

Each contributes one gene to their child. Since John is type AB, he only has A and B genes to contribute. Janis has an A and an O. Since O is recessive to the other two types, two O's are needed for the child to have that blood type. He gets only one from his mother.

3.       Is it possible for Stacie and Harry to have a child who is type O?


If Stacie is heterozygous for type B (BO), then they could have type O children. After all, Harry is type O, so he contributes only O genes. Stacie, if heterozygous, would contribute one O.

4.       Len and Claire and Melanie and Bob were in the same hospital at the same time when they had their respective babies. Len and Claire had twins, a boy, James, and a girl, Jill. Melanie and Bob had a boy, Howie. After being home for a few days, Claire was convinced that she had the wrong boy. There must have been a mix-up at the hospital. After all, her kids were twins, and even though they were fraternal twins, you would think that they would look a lot more alike than they do-one is blond and the other is brown-haired. At their insistence, blood types were taken on both their family and Melanie and Bob and their son. The results were as follows:

Claire is type B
Len is type AB

Melanie is type B
Bob is type A

James is type B
Howie is type O
Jill is type A

Was a switch made at the hospital?


How do you know?

The student should answer that Len and Claire couldn't possibly have a type O child since Len is type AB.

Melanie must be type BO and Bob must be type AO since Howie is type O. Each parent contributes one gene to their child. Len couldn't have a type O child since he only has A and B genes to contribute.

This is another example of forward and backward reasoning. Also, sideways reasoning. Students must compare the two families. Students must also dredge up memories of meiosis to remember how chromosomes are distributed during gamete formation and how fertilization joins the two sets of chromosomes from the gametes.

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