If offspring is O+ what blood type would parents have to have to make this possible?


closed as off-topic by rg255, MattDMo, anongoodnurse, fileunderwater, AliceD Mar 30 '16 at 8:57


  • "Homework questions are off-topic on Biology unless you have shown your attempt at an answer. For more information see our homework policy." – rg255, MattDMo, anongoodnurse, fileunderwater, AliceD

  • $\begingroup$ Is this a homework question? $\endgroup$ – Remi.b Mar 29 '16 at 20:11
  • $\begingroup$ Homework questions and trivial questions about basic biological concepts are off-topic on Biology unless you have shown your attempt at an answer. For more information see our homework policy. In this case, the question can be answered by a careful reading of the Blood Type Wikipedia page and its links. Please do your own research, and share that research, before asking a question. $\endgroup$ – MattDMo Mar 30 '16 at 1:06
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    $\begingroup$ OK. Let's assume it is a homework question. There still seem to be people interested enough to comment who don't seem to have a grasp of simple Mendelian genetics. Wouldn't it be better to change the question to "How do I determine the blood types of parents that could produce offspring with the O+ blood type?" Then one could stress that they need to distinguish genotypes from phenotypes, determine whether the trait observed in the genotype is dominant or recessive, and establish the possible genotypes each phenotype could have. Then do the crosses. Reference to a basic genetics book to help. $\endgroup$ – David Mar 30 '16 at 20:14

The parents of a child with 0+ have the blood group A, B or 0, but not AB. And one or both parents are positive regarding the Rhesus-Factor (+).


There are several factors and derived systems that allow a classification into blood groups. Your example covers two: the AB0-system and the rhesus-system.

The AB0-system covers four groups: A, B, AB, and 0. In other words: people either have factor A, factor B, both factors or none. People with factor A either hand this factor down to their child, or they don't. Accordingly, people with factor B either hand it down or not. People with AB in any case hand down one factor, either A or B. People without a factor (group 0) can't hand down A or B. Given those rules, a child with griup 0 did not inherit factor A nor B. So the parents of this child don't have group AB, but can have any of the other three groups.

The rhesus-system is about having (being positive, +) or lacking (being negative, -) an other factor, the so called Rhesus factor. A rhesus- positive person either does or doesn't hand down this factor to his/her children. A rhesus-negative person has nothing to hand down. Thus, knowing that the child in your example is rhesus-positive, it did inherit this factor from at least one of its parents. This, one can assume that one or both parents also carry this factor.

Final remarks:

  1. There can be rare exceptions from the above mentioned rules.
  2. There are more details about this topic worth reading. However, I skipped them to keep the answer readable.
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    $\begingroup$ @downvoters Would you please leave a comment about what's wrong with the answer? I could try to improve it $\endgroup$ – Arsak Mar 29 '16 at 20:55
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    $\begingroup$ Better a diagram showing both alleles of the parents which can give OO offspring, just for ABO, e.g. AOxAO, BOxBO, AOxBO, AOxOO and BOxOO. Then the intelligent reader will be able to see why no parent can be AA, AB or BA. For Rh you need to spell out that Rh+ is ++ or +-, and Rh- is --, the reader should be able to work out why one parent must be Rh+ and the possible combinations. But a picture is often worth a thousand words. $\endgroup$ – David Mar 29 '16 at 23:09
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    $\begingroup$ No. But the level of ignorance in the comments makes me think something is needed. If this really is a homework question then perhaps it could be rephrased as "How would I find out…". I'll think about it. $\endgroup$ – David Mar 30 '16 at 18:58
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    $\begingroup$ @David Based on the comments I assume it could be an urgent real life question rather than homework. Like 'my brother made this blood test and is now afraid he was adopted' or so... (speculating). $\endgroup$ – Arsak Mar 30 '16 at 20:24
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    $\begingroup$ Yes, he said it was. But the moderators disagreed, so I presume the question will disappear. As your answer is correct, he will already have the info. I was just thinking what else positive we might do with the situation. $\endgroup$ – David Mar 30 '16 at 22:51
