Anyone know anything about blood types?

[BerryPieandCustard]

So recent discussions with my mum and sister have made me think about if me and my sister are in fact full sisters. According to my mum we are, she does however admit that when my parents divorced when I was 13 and my sister 9 that my dad questioned if my sister was his child?!

Mums blood group O positive
My blood group B positive
My sisters blood group A negative, when pregnant it was discovered that she has something called thallasemia trait (apparently more common in Middle Eastern/Mediterranean people than white British)

I have asked my dad his blood type but he doesn’t know.
Does that mean that my dad would need to be blood group AB negative (quite rare I think?) to be the father of both of us?

Of course it could be that I am not his biological child or that neither of us are?! Given the fact that my parents divorced due to my mums infidelity and the way in which she chooses to live her life nothing would surprise me tbh.

Positive is dominant over negative so your dad could be AB+ or AB-.
Does your sister have thalassemia trait (one copy) or thalassemia (two)?

He would need to be type AB, but could be Rh+. If he and your mum both carried Rh+/Rh- genes they would themselves be Rh+ but could both pass on Rh- gene resulting in Rh- child.

He would have to be blood group AB but could be either rhesus positive or negative.

To be rhesus positive you need to inherit at least one rhesus positive allele from your parents, to be rhesus negative you need two negative alleles.

Your mum must have one positive and one negative allele, as she is rhesus positive but has passed on a rhesus negative allele to your sister. Your dad could either be the same or have two negative alleles.

@drspouse she has Thalassaemia trait, so one copy

Sorry I didn't read. So one of your parents has thalassemia trait but it does happen in other groups.

Ah ok... so my dad needs to be AB but could be positive or negative.
If he is only A or B blood group then he will only be the father of one of us.

Basically, yes.

OP, if he is the man who raised you, cared for you, provided for you, loved you, then he IS your father in every sense that matters. If any other man was involved, they were a mere sperm donor.

It is important to know about your biological origins, though, even just for health reasons. Your parentage "matters" in this sense - "mere sperm donors" give you your physical body and your medical risks.

If you really want to know the genetic relationship between you and your sister you could each do genealogical DNA tests from e.g. 23&Me which (if you link your profiles) will tell you how much DNA you share. At about 25% shared DNA you would be half-sisters, at about 50% full sisters.

Don’t go there if there is any risk of upsetting family members with the results though - these things need to be approached with sensitivity.

It's not really the children's responsibility to care for their parents, though, is it? Even if the children are adults.

My sisters blood group A negative, when pregnant it was discovered that she has something called thalassaemia trait (apparently more common in Middle Eastern/Mediterranean people than white British)

My DF is Italian, DM was English. I have 2 DBs. We all have O -ve blood but only one of us (my younger DB) picked up "beta thalassaemia minor". Which he only discovered when he moved to the US and someone said "you name is Italian isn't it ? You should get checked for this" - aged 25.

If that helps ...

Whatever blood comes from DFs side of the family must be quite odd ...

I think AB is also more common in southern European countries.

Also, while you may not know of any Mediterranean ancestry in your family, it's possible that someone else in the family has a biological father that is not their legal father - e.g. either of your parents, or any of their parents. Plus these traits (thallasaemia and AB) are not zero in the UK.