For example if among your parents to be AB+ and the other was O+, they could only have actually A and B kids. In other words, most most likely none that their children would share one of two people parent’s blood type.

You are watching: Do brothers and sisters have the same blood type

And that’s simply one of plenty of possibilities. There are lots of other possible combinations where 2 parents there is no blood form A have the right to have a kid with one. Right here they are:


Now regarding the confident part, that adds even much more possibilities. Here is a table that ns think goes with all the feasible combinations whereby an A+ person would have actually a different blood form from his or her parents: 


So over there you have it. At least ten various combinations that parents there is no an A+ blood form can offer an A+ blood type.

Before relocating on, the is probably vital to cite that there may be rare exceptions whereby an A+ child can come native parents with a different mix than among these. Have actually a look through our previous answer on blood type to see how this could happen. 

What I thought I’d do for the rest of the price is emphasis on why this combinations have the right to all give an A+ blood type. As you’ll view it needs to do v two different genes and the different versions lock come in. 

Alphabet Soup: exactly how A, B, and O space Different

First let’s go over a tiny bit around what it means to be A positive.

Blood cells naturally have actually lots of different sugars on their surfaces. The street that physicians look at to determine one component of your blood team come in three flavors – “A,” “B,” or “O.”

As you could have guessed, the A flavor provides the A sugar, and also the B one provides the B sugar. It turns out that the O flavor doesn’t make any sugar. 

Your blood form is established by which mix of sugars you have. And also this is identified by the genes you get from your parents. 

Two copies of every Gene, One from each Parent

DNA is a set of instructions because that making and also running a living thing. So your DNA is the set of instructions for making and also running you.

A the majority of these accuse are found in lengthy stretches of DNA dubbed genes. Each gene has actually the instructions for one small part of you.

One that these gene goes by the name ABO. It come in three flavors, or “alleles” —A, B, and O. Your blood form is figured out by the combination of alleles that this gene you get from her parents.

When girlfriend inherit a gene, friend usually obtain two copies, one from your female organic parent and one from your male one. What this way for the ABO gene is that you have the right to only have actually two the the three alleles the the ABO gene. The complying with chart shows you the different combinations that are possible: 


Now here’s the component that’s a little complicated. Once we talk around someone’s blood type, we treatment less about the gene combinations, and much more about what castle able to make. Because that example, someone it is “AO” will certainly be type A, since the O flavor of the gene provides no sugar. This human only has actually the A sugar.

Here are the blood types associated v each of the combinations of alleles: 


As you deserve to see, also though there space 6 different allele combinations, over there are just 4 different blood types.

Now we have every little thing we need in order to explain how two parents there is no an A blood kind might have actually a boy with the A blood type. Here is an example of among the ways we talked around in the very first section: 


In this example, your female biological parent is ab and your male one is O. Remember us only obtain one of one parent’s 2 copies and also one that the various other parent’s. 

In this case, one offered you an “A” and also the other provided you one “O,” so you’d be “AO.” This way you are the A blood type.

(I believed it would certainly be necessary to cite that no every family members looks favor the household in this instance – you may have two dads or two moms, who had actually you v the assist of a donor. However, girlfriend would gain your blood type from your female organic parent and also your male biological parent.)

Another Gene determines Positive/Negative

So now I recognize what you’re thinking – you A positive, therefore what go the “positive” component mean? It transforms out there’s another important molecule on blood cells referred to as the Rh protein.

You either have the Rh protein or you don’t. If you have actually it, you positive, and also if girlfriend don’t, she negative. If you interested in knowing an ext about the Rh protein, you deserve to visit one of our ahead Ask a Geneticist answers.

As through the ABO sugars, one gene controls your Rh type. This gene comes in either a “working” kind – an interpretation it provides Rh protein – or a form that renders no protein at all.

For girlfriend to it is in A positive, you must have actually inherited at the very least one functioning copy of the Rh gene from among your parents. However, we don’t recognize for certain if one or both of her parents is Rh positive.

Instead of drawing out every combination of ABO and also Rh, listed below is one instance of exactly how you can be A hopeful with neither of her parents gift the exact same blood form as you: 


Here, the female biological parent is AB negative and the masculine is O positive. The female has an A allele and also a B allele for she ABO gene, and also two negatives for she RH gene. The male has two O alleles the the ABO gene, and also a confident allele and also a an adverse allele the the RH gene.

See more: How Old Do You Have To Be To Drink In The Bahamas, How Old To Drink In The Bahamas

In this case, the female happened to pass an A and also a negative, and the male an O and a positive. Therefore you room “AO +/-” genetically, definition you have actually an A+ blood type.

We hope you enjoyed learning about blood types! If you’re quiet curious around blood types, consisting of how and why the body doesn’t expropriate blood the doesn’t look favor its own, inspect out this valuable link.