Blood types

If both parents have blood type O can they have a child with B negative blood

[ducky406]

No and yes. Type O blood type is caused by the recessive gene of O,O alleles. That means that the only allele a person with type O blood can pass  down is O. Someone with B type blood must have the genotype B,O-so one that person's parents must have to have a B blood type or an A,B blood type in order to pass that down.

HOWEVER there is a VERY rare condition that I studied while I was taking genetics. I just can't remember what it's called. I thought it was something like Pompeii syndrome I can't find it and my text book is in storage. :/ Anyway the ABO blood typing is decided on based on the antibodies and sugars that hold to the blood cells, and in this freakishly rare disorder the sugars don't hold on to the blood cell. So a person can show type O blood while in reality not being type O at all. Basically a person can really have type B blood and have those antibodies that show they're type B floating around, but because of a mutation that antibody won't stick to the blood cell and it looks like they have none. This is the only way it's genetically possibly for a parent to show type O blood and have a child with B (Or for a parent with A,B to have a child with O). But this is a very very rare disorder that really only shows in people with a very specific ethnic background (I believe from only one part of Italy). So while it's theoretically possible it's extraordinarily improbable.

The negative or positive comes from a different gene. A positive Rh is dominant to negative. So if someone has the genotype +/- they would show positive. If both parents are positive there could be a 25% chance of having a baby with a negative Rh type. However, this can lead to problems. My sister in law was told that this could have been the reason she miscarried one of her babies and it caused some major health problems for one of my nieces. Because the baby was Rh-, her immune system was fighting off the maternal blood which lead to a severe case of anemia. She's fine now, but it initially caused a lot of problems. On the reverse if a mother is negative Rh and has a baby with +/-, she herself could die. The baby's blood would get mixed into the mothers and the mother's immune system would attack the fetus; usually causing a miscarriage and making the mother very ill. SO if a person's parents are both Rh+ they can have a baby with Rh- blood type; however if both parents are Rh- they cannot have a baby with a Rh+.

If you are worried that you are type B and your parents O, or that your baby is B and you and your partner are O I would suggest retesting the blood type first. Then I would suggest maybe looking into seeing if someone was unfaithful, the hospital messed up, or someone was adopted.