If I am blood type B, what are all the possible genotypes that could be expressed by my parents?

I think it might be 16 but I was reading online and saw this:

Similarly, someone who is blood type B could have a genotype of either BB or BO.

So if someone can help me answer this, that would be great.


2 Answers 2


Parent 1 and 2 have each 5 possible genotypes (OO, AO, BB, BO and AB).

Here a Punnett square with each possibilities. I highlighted the possible parent genotypes.

enter image description here

The total number of possible crosses is exactly 21. Note that here A = Ia, B = Ib and O = i.


This is starting from the information based on your blood type only (i.e. no information about your genotype).

Some background information. Antigen expressing alleles (here referred as Ia or A and Ib or B) are dominant. Not expressing an allele is notated i or O. Being of blood type O is when you don't express both alleles so it is a recessive trait (only possible genotype is ii or OO genotype).

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    $\begingroup$ You probably shouldn't call an AB individual homozygous. $\endgroup$
    – canadianer
    Commented Mar 25, 2015 at 18:41
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    $\begingroup$ @canadianer thanks for pointing that out. Modified the table. $\endgroup$ Commented Mar 25, 2015 at 18:48
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    $\begingroup$ Your answer is better, so I'll just delete mine to avoid confusion. $\endgroup$ Commented Mar 25, 2015 at 18:58
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    $\begingroup$ @poka.nandor was getting messy without a table ;) $\endgroup$ Commented Mar 25, 2015 at 18:59
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    $\begingroup$ @cagliari2005 yeah I should have done the same to avoid missing possible crossings. I feel bad about it... I mean not about you having a better answer, but about me being careless. $\endgroup$ Commented Mar 25, 2015 at 19:01

21 crosses could be many more if you considered minor types as A2, A3, B3 or hybrid alleles as Ax, Bx or chimera AB alleles as cis-AB, B(A). These rare phenotypes break standard 4 type rules, for example, Ax/O genotype could be both type A or type O. It depends if you talk about genetcis or blood compatibility.


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