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Nobody in my family has the same blood type. My mom is A, my dad is B, I’m AB, my brother is O. How is this possible? |
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June 2005
What a great question! Don’t panic – everyone
in your family can still be related according to blood type.
Unless you didn’t want your brother to be related :)
First, we need to understand blood types. Red blood cells
(rbc) are classified by the chemical (antigen) on their surface
– either A or B. If there is no antigen, the rbc is
type O. The presence of A or B makes the rbc the corresponding
blood type. A and B can co-exist on the surface of the rbc
and that leads to the AB blood type. Genes controlling the
ABO system are found on the long arm of chromosome 9 and you
inherit one copy from each parent.
Your Family
|
Blood Type |
Antigen |
Genotype |
| Mom |
A |
A |
AA or AO
|
| Dad |
B |
B |
BB or BO
|
| You |
AB |
A & B
|
AB |
| Brother |
O |
Neither |
OO |
In your family, the inheritance all works out if we assume
that your parents are both heterozygous and carry the gene
for the O blood type.
| Mom/Dad |
B
|
O |
| A |
AB (you)
|
AO (blood type A) |
| O |
BO (blood type B)
|
OO (your brother)
|
If you have siblings with A or B type blood, you’ll
be able to explain that too!
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