You have two copies of each of your chromosomes, one copy from each parent. The blood type gene resides on chromosome 9. Each copy of chromosome 9 contains one blood type gene: an A gene, a B gene, or neither (O). The variants are referred to as alleles.
Sex cells (egg, sperm) contain only one copy of each chromosome. When the two meet up, you get the combination that will define the resulting individual.
I look more like my great-great-uncle from what I remember in old family photos. Assuming he was an asshole, I probably got my asshole behavior from him too.
Let’s say your mom is AB (which she is) and your dad is AA (he might have been other combinations but let’s make it AA for the sake of the exercise; since you don’t mention him being AB I’m assuming he was not; if his blood type was 0… I’ve got bad news). The AB0 group is all in the same site, there is an A gene which makes A protein and a B gene which makes B protein and a third gene which doesn’t make either A protein or B protein. There is no AB gene, someone AB has one A gene and one B gene.
OK, so y’all being AB means you got either one of your Dad’s genes but all of you got Mom’s B side. There could be something on the A side which makes that one a worse match for Dad’s own material, but since we don’t know that there is we’ll just treat this as “both A and B sides are just fine”: that means either of you had a 1 in 2 chance of getting either side.
So the chance of one of you being AB was 50% (1 in 2). Two of you, 25% (1 in 4). Three, 12.5% (1 in 8). And all four, 6.25% (1 in 16). Which ok, is better than the odds for the Euromillion and people play that game, but still pretty low.
As for the +, that’s a different gene site and I’m feeling too lazy to do the math.
Interesting question! I have met many who wondered if their dad was their dad, yet believed their mother was their mother, but don’t recall anyone ever believing their mother wasn’t their mother but that their dad was indeed their dad.
I look like my mother, and her mother before her. So much so, that one picture I have of my maternal grandmother has fooled even close family members into thinking it was me in the picture. When we would visit my mother’s small hometown in Germany, none of her classmates had any doubt whose daughter I was! My dad used to joke that if it weren’t for my crooked pinkies, I’d have nothing from him.
There was an interesting pause in the conversation at a dinner table one day when my sister announced that the result of her blood test was Type B. My mother is Type O. My father was Type A.
My mother is extremely religious and the odds of us children having a different father seems, well, inconceivable.
As it turns out, my father’s reported blood type was an error, and he really was Type B, as am I.
Too bad, it would have been a better story.
Another note: I’m the forth of four children born in less than four years. When I was conceived, I had a four-month-old sister, a 18-month-old sister and a 35-month-old brother. I doubt my mother had any time for an affair.