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Question Video: Determining the Possible Blood Groups in an Offspring Biology

A man with blood group B married a woman with blood group A. It is impossible for them to have a child with blood group _.

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Video Transcript

A man with blood group B married a woman with blood group A. It is impossible for them to have a child with blood group blank. (A) B, (B) AB, (C) O, or (D) none of the above.

This question asks us about blood group, which is determined by multiple alleles in humans. An allele is just a different form of a gene. The alleles for the primary blood type or blood group gene are A, B, and O.

Interestingly, the A and B alleles exhibit codominance. This means that if they are both inherited, a person will have blood group AB, where both dominant alleles are expressed instead of just one or the other. On the other hand, the inheritance of two A alleles or one A and one O will produce A blood type. Similarly, the inheritance of two B alleles or one B and one O will produce B blood group. That is because the A and B alleles are dominant to O, which means that they will always be expressed if they are inherited.

The O allele is recessive. This means it requires two copies in order to be expressed. It will always be masked in the presence of a dominant allele like A or B.

Now let’s return to our question. We are asked about a man with blood group B and a woman with blood group A, though we aren’t told if they also possess an O allele that is being masked. Therefore, the man could potentially have the alleles B and O, while the woman could have A and O. Let’s create a Punnett square using these alleles to see what kind of offspring can be produced.

To create a Punnett square, we first need to list the alleles of the biological mother and the biological father on the tops and sides of our square. Then for each potential offspring, we can combine the alleles from the row and column it belongs to. For instance, the first offspring in this grid would inherit an A and a B allele. If you continue to solve this Punnett square, you will see that the offspring can also inherit the alleles AO, BO, and OO.

So which blood groups would this produce? AB produces blood group AB, since the A and B alleles are codominant. AO would result in blood group A. BO would produce blood group B. And OO would result in blood group O since it has two copies of the recessive O allele. Therefore, this cross could potentially produce offspring of all four blood groups. So the correct answer to our question is answer choice (D). A man with blood group B and a woman with blood group A could have a child of any blood group. Which blood group would it be impossible for their child to have? None of the above.

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