question about blood tyes?

Question

if a mom has blood type a and the kid has o blood, why couldnt a father with ab blood be the dad, and why could one with blood type a be the dad???

blood types*

Answer 1

I know where you're getting confused.

To keep it simple (and simply ignore the RhD antigen which creates the positive or negative blood type), Type O is considered to be the "universal donor", while Type AB is considered to be the "universal receiver". So if a person with Type A, B, AB, or O is getting a blood transfusion, their body can use Type O blood.

But because of the way genetics work, in order to produce a child with Type O, either the mother or the father has to be Type O. If the father has Type AB and the mother has Type A, then the child could have Type A, Type B, or Type AB, but never Type O.

Answer 2

Ignoring the Rh types.

There are 3 main types of antigens (what the surface of the blood looks like), A, B, and o.

Captial letters denotes that the phenotype (what is actually expressed by the gene) is a dominant gene. If you have a dominant gene, that's the one expressed.

Lower case letters denotes that the phenotype is recessive. If it's recessive, it won't show if it's paired with a dominant gene - it'll only show if you have two of the recessive genes.

Following genetics, you get one gene from your mother and one gene from your father. (Everyone has a set of 2 of the same gene.)

For someone to have type A blood, then they have either AA (one A each from their mother and father) or type Ao (one A from one parent, one o from the other parent)

For someone to have type B blood, then they have either BB (one B each from their mother and father) or type Bo (one B from one parent, one o from the other parent)

In genetics it occasionally happens that two dominate genes can both be expressed at the same time (codominate). This is the case with type AB blood, where an A is from one parent and one B is from the other parent.

For someone to have type O blood, then they have to have oo, one o gene from both parents.


Using these little boxes: on the outside are the genes that the parents pass on, and inside the boxes are the possible children that those parents could have. I'm only going to do the pair matching for your listed individuals.

A | A
-------------
A | AA | AA
-------------
A | AA | AA

A | o
-------------
A | AA | Ao
-------------
A | AA | Ao

A | o
-------------
A | AA | Ao
-------------
o | Ao | oo

o | o
-------------
o | oo | oo
-------------
o | oo | oo

A | B
-------------
A | AA | AB
-------------
A | AA | AB

A | B
-------------
A | AA | AB
-------------
o | Ao | Bo

well, you get the idea to contine such charts... an AB parent cannot genetically have a type oo child. However, a type Ao, Bo, or oo parent can have a type o child. A type oo parent cannot have a type AB child... and there are other impossible combinations...

Answer 3

Each parent donates part of the offspring's new blood type. To keep it real simple, if any parent has AB, the child cannot be O. O is recessive, and required no other letter to be present. Obviously, if a parent has AB, s/he will donate either an A or B, and the child cannot be O. Also, it is important to remember that two blood types are included in RBC. Hence blood type A can have the genotype AA or AO. If it is AO, then the offspring can receive the O

Yes, I know the letters are representative of the antibodies, but I wanted to keep it simple.

Answer 4

Blood type A is dominant to recessive blood type O.
So is Blood type B. Blood types A and B are co-dominant. This means that neither shows dominance, hence the blood type AB. In order for a recessive allele (in this case O) to be shown in the offspring, BOTH parents must have donated this recessive allele. Therefore, a mother with the blood type A may have the genotype of heterozygous Blood type A, meaning one allele A and one allele O. The father therefore, cannot have the blood type AB, because this would mean he did not possess the recessive Allele O to pass on to the child.

Answer 5

The blood types result from a person having a certain "flag" (or more properly "antigen") on the surface of blood cells. These result from a combination from 2 genes...

Each gene spot may be either A, B or O

if you are OO - you have blood type O
if you are AA or AO you have blood type A
if you are BB or BO you have blood type B
if you are AB then you have blood type AB

If the kid has blood type O (OO) then (s)he must inherit an O from mom AND from dad.

Mom is blood type A and could be AA or AO... but would have to be AO to donate her O

Dad cannot possibly be AB... and must be O, A (ie AO) or B (ie BO)

Answer 6

If you look at genetics, you find that the parents do not produce precisely identical zygotes. There are all sorts of minor variations in the genetic coding that produce different results. That's why you don't look like a precise copy of your brother or sister (if you have one) despite being spawned from the same parents.

Then there are dominant and recessive genes -- such as blue eyes versus brown eyes. Brown eyes are a dominant gene, and can result from the following possible pairing from your parents:

Let's say your grandfathers both had brown eyes (dominant gene code BB), and your grandmothers blue eyes (recessive gene code bb). Your father then would have brown eyes three chances in four -- BB, Bb, bB -- and only one chance in four of blue eyes -- bb. Assume the same situation for your mother.

So, you have both parents with brown eyes (Bb and bB), yet the baby is born with blue eyes. How could that possibly happen?
Simple, both parents have the recessive b gene for blue eyes, and in one chance in four, you get both recessive genes:

Bb + bB ===> BB, Bb, bB for brown eyes, bb for blue eyes.

The same thing could happen with blood types. The key is the genetic code passed along by the parents, and what dominant/ recessive gene combinations are expressed. I'm not sure on which blood types are dominant and which are resessive, but the principles are the same.

Answer 7

The blood type has to match one of the parents, you don't get a third blood type in this situation. Just the nature of it.

Answer 8

one of the childs blood types has to match one of the parents...it has to be the same...i can be either negative or possitive (i think).

Answer 9

The bigger question begging to be asked is who's the real dad? Mom's secret is out....