My both parents have the same blood group which is B+ and I am O- ! How can this happen?

You need to know more than just blood type, what is the genotype of each parent, BB or BO or BA So a further blood typing will need to be do

https://www.askmehelpdesk.com/pregnancy-new-motherhood/can-father-blood-group-b-mother-blood-group-b-give-baby-o-506687.html

Blood type - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Blood_type)

My both parents have the same blood group which is B+ and I am O- ! How can this happen ?!

As Fr_Chuck said, it gets fairly complicated as there can be many, many combinations.

To try and put it very simplistically:

Mom and Dad are both B positive. The B is for blood type, the positive for Rh, which is a protein on the blood cell. They are both B from the dominant gene in a BO blood type combination. The gene passed on to you was the recessive O. You received one from each thus your blood type is O.

The same thing happens with the Rh protein. They are both positive with a postive/negative combination, with the positive being dominant, and you received the recessive negative. Which made you O negative.

You will have to keep this in mind if you go onto have children of your own if your partner is Rh positive as this can become something that will need to be addressed if your baby is Rh positive as well. Some women will develop antibodies after a first pregnancy in which they will need to have injections of what is called rhogram to insure a healthy baby next time.

That's a basic explanation of it... hope that helps.

Can a father with blood group B+ and a mother with blood group B+ give a baby with B- ?