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There’s a lot of phenotypes that are easy to tell. Your eye color, your hair texture,
your height, whether you have a straight thumb or hitchhiker thumb.
But one phenotype that you can’t just tell by looking is your blood type. Your blood
is really made of many things----platelets, plasma, and red blood cells.
But you have probably heard before that when blood is donated, it’s important that it
is matched correctly? And that’s true, because blood type phenotypes vary. It really boils
down to the fact that red blood cells are not naked. They have proteins on their surface.
And it turns out that your immune system is very protective and if it gets blood donated
that have different proteins that it’s not used to, it will attack them!
With blood type, you can have several different phenotypes: A, B, AB, or O. These letters
stand for antigens that are found on red blood cells. So type A blood, for example, has A
antigens on the surface of red blood cells. Type B blood, for example, has B antigens
on the surface of red blood cells. Type AB blood has both A and B antigens on the surface
of red blood cells. Type O---I like to think of it is looking like a zero---it doesn’t
have A or B antigens. It’s naked! Well, ok, it does have other proteins on its surface.
But not A or B. So think of O as looking like a zero! It doesn't have A or B.
So if you are type B blood, you have B antigens on the surface of red blood cells. That means,
a person with type B can accept another person's type B blood because
B is an antigen their body recognizes.
But if you try to give that person a type A blood type, that's an antigen that
the immune system does not recognize. That person's immune system will attack! It would also attack AB blood, because
that includes the A that it doesn’t recognize. Now Type O would be safe though. Remember O looks
like a zero---it doesn’t have A or B antigens. So type O can donate to everyone!
Now while O individuals can donate to everyone, they can only receive blood from another type
O. Because type O blood does not have A or B antigens, their immune system will attack
any other blood type that does.
Neither of us have type AB blood, but we would think this is a cool blood type to have in the sense
that you could receive blood from anyone. If an AB person received blood from a person that had Type A,
well they’ve got the "A" so it’s all good. And if an AB person received blood from
a person that had type B, well they’ve got the B antigen too, so it’s all good. They can receive blood from type
O too because there are not any antigens to even worry about.
Now one thing we want to add that makes all of this a bit more complicated---blood types
also have a plus or minus sign listed by the blood type. This makes a big difference
with blood donations. If you have a plus, it means that you have this other little protein
called Rh factor on the surface of your blood cells. If you have a negative, it means that
you do not have this little protein called Rh factor on the surface of your red blood
cells. We are not going to be able to go into that in this short clip so---to the google
for that if you would like to learn more about this.
Blood type is genetically inherited and a great example of multiple alleles. Remember
that alleles are a form of a gene---like a flavor. Just an analogy.
So let’s put this into practice. Let’s say a couple gives birth to a baby boy. Both
parents have type A blood. But then, there was a mixup at the hospital! And now----haha,
sorry I get real into my drama----there are these two baby boys and the hospital doesn’t
know which one belongs to the couple! Probably not a hospital where you want to have kids
but let’s try and use our blood type genetic problem solving skills to help out here.
Baby Phil has Type B blood and baby Sylvester has Type O blood.
Could either of these babies
belong to the couple, who both have type A blood?
Well let’s talk phenotypes and genotypes. The phenotype of type A blood is A. But the genotype
is written like this or this. This format of writing here helps with multiple alleles like
blood type problems, and we can show you why when we work out the Punnett square.
Now you may notice that I said that blood type A can be written this way or this way. Without testing,
we don't really know which one it is.
You can consider this one to be homozygous and this one to be heterozygous.
The phenotype of type B blood is B. But the genotype is written as this or this.
The phenotype of type AB blood is AB, and the genotype is written this way. There is no other way to write that one.
The phenotype for type O blood is O. And the genotype is written like this.
Remember how I said that the O kind of looks like a zero and so you can think of that as having zero blood
type antigens? Well, that’s what it is. ii. No coefficient.
Ok, back to the babies. We are told the parents both have type A, but remember that we don’t know whether that means
they are this type A, the homozygous, or this type A, the heterozygous. And the mom could be one of those genotypes and
the father could be the other genotype---or they could both be the same genotype--
we just don’t know.
Ok, so let’s just try it out with all of the possibilities. Remember that we write the parent genotypes
on the top and side of the Punnett squares, like this. We'll fill in the squares and we'll make
sure to have capital I’s first just for formatting purposes.
Ok so is it possible to get baby Phil---who has type B in any of these offspring?
He must be someone else’s baby.
What about baby Sylvester with his type O?
YES! It is possible but both parents would have to be heterozygous A
--that means they both have to be this----then, yes, you would have a 25% chance (that's 1 in 4 here) of having
a baby with type O blood.
Of course, if I was advising the couple, I would also insist on a DNA test as this blood
type problem only shows that it’s possible that baby Sylvester is theirs. Well that’s
it for the amoeba sisters---and we remind you to stay curious!
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