Blood Type and Genealogy

I have recently been doing a mini sideline project collecting all the Blood Types of all the members of my family and linking them into the family tree. This has been an interesting little exercise in which I have learnt quite a bit about Biology and even a little about my recent Genealogy.


Even though this is not a Y-DNA or mtDNA subject I guess it is still a DNA topic of a sort - it could even be a very basic way to help prove or disprove relationships.


I am a B+, my Mother is O+ and my Father is B+.


This means that I was passed the genes for B rhesus + blood group from my Dad and the genes for O rhesus + from my Mum. B is dominant over O which is why I turned out as a B. As both are rhesus + I turned out +.


  • B is dominant over O
  • A is dominant over O
  • A is co-dominant with B
  • B is co-dominant with A
  • rhesus+ is dominant over rhesus-


It is very difficult to know what your recessive blood type gene is, however you can sometimes work it out.


  • If your (Phenotype) blood type is O, this means that both your (Genotype) genes are O; this is because you know that neither parents contributed an A or B otherwise one of these would have been dominant and made you A or B.
  • If your (Phenotype) blood type is AB, this means that your 2 (Genotype) genes are A and B; from this you can deduce that neither of your parents are O because you must have inherited an A from one parent and B from the other therefore your parents must have been either A, B or AB.
  • If your (Phenotype) blood type is A, it gets a little more difficult. Your 2 (Genotype) genes could be either A and A or could be A and O (but you know they are not A and B - otherwise you would be AB).


More information can be found on the Wikipedia page http://en.wikipedia.­org/wiki/Blood_type which goes into more detail about the subject.


Where this could be useful in Genealogy is where you may be able to work out that blood groups do not fit correctly between parents and children (uncovering skeletons in cupboards!). You can also try and work out the blood type of relatives who do not know their blood type based on what you do know from others.