From my understanding (only high school biology ) there are dominant and recessive genes involved too. I'm O+, but both my parents are A+. (Had a bit of a go at them when I found out as a teenager that I had a different blood type to them: "Why didn't you tell me I was adopted" etc etc... Confused parents replied, "But you weren't..." ) Turns out that it's possible because the O gene is recessive and mum and dad each carry an O gene which is how I ended up with that blood group. I wonder if it works the same way with the RH-ve part? That the +ve part is the dominant gene, therefore if one parent is +ve the baby will be +ve? Anyway, given that you are RH+ve you don't need to worry. Out of interest, did your mum have any subsequent kids after you?