A+
A-
B+
B-
AB+
AB-
O+
O-
Your blood type is inherited from both of your parents. Each parent carries TWO "alleles" for both blood group and Rh factor, of which only ONE is passed to each offspring. What alleles they possess constitutes their genotype. Some alleles dominate over others. For example, a parent with type A+ may have 2 "A" alleles, or, they may have one A and one O. In the latter case, the O will be dominated by the A, and that person will be blood type A, but can still pass the O trait on to a child. Similarly, a person who is Rh+ may have either two + alleles, or one Rh+ and one Rh-, with the Rh+ dominating. Again, in the latter case, they may pass either an Rh+ or Rh- allele to their child.
An A or B allele will dominate over an O, so if your genotype is AO, you will be type A, and if it is BO, you will be type B. People with both an A and B allele have type AB, since neither dominates the other. Since the O allele is recessive, people with type O blood will always have the genotype OO. The Rh+ allele dominates Rh-, so a person with a positive Rh factor may be ++ or +-. Those who are Rh negative are always --.
It is not usually possible to determine a person's genotype (what specific alleles they carry) with a conventional blood typing test, so the last two charts on this page represent the possible/impossible outcomes based on the blood type alone. The only blood types for which the genotype can be specifically determined are AB-and O-, however, it can sometimes be determined by the parents' blood type. For example, if you have type B+ and your mother is O-, then you know that you have a dominant B allele and one of her two recessive O alleles, and that you possess a + Rh allele and one of her two - Rh alleles, there for, your genotype is BO+-. Or, if you have type B+ and your father is AB- and your mother is AB+, you know must have inherited B alleles from both parents, as well as a + Rh from your mother and a - Rh from your father, and you are therefor BB+-.
A+ |
O+ |
B+ |
A- |
O- |
AB+ |
B- |
AB- |
|---|---|---|---|---|---|---|---|
| 3400 | 3400 | 1275 | 600 | 600 | 425 | 225 | 75 |
A+ |
A- |
B+ |
B- |
AB+ |
AB- |
O+ |
O- |
|---|---|---|---|---|---|---|---|
| AA++ | AA-- | BB++ | BB-- | AB++ | AB-- | OO++ | OO-- |
| AA+- | AO-- | BB+- | BO-- | AB+- | |
OO+- | |
| AO++ | |
BO++ | |
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| AO+- | |
BO+- | |
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| Parents' Blood Types | A+ |
A- |
B+ |
B- |
AB+ |
AB- |
O+ |
O- |
|---|---|---|---|---|---|---|---|---|
A+ |
A+, A-, O+, O- | A+, A-, O+, O- | ALL | ALL | A+, A-, B+, B-, AB+ AB- | A+, A-, B+, B-, AB+ AB- | A+, A-, O+, O- | A+, A-, O+, O- |
A- |
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A-, O- | ALL | A-, B-, AB-, O- | A+, A-, B+, B-, AB+ AB- | A-, B-, AB- | A+, A-, O+, O- | A-, O- |
B+ |
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B+, B-, O+, O- | B+, B-, O+, O- | A+, A-, B+, B-, AB+ AB- | A+, A-, B+, B-, AB+ AB- | B+, B-, O+, O- | B+, B-, O+, O- |
B- |
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B-, O- | A+, A-, B+, B-, AB+ AB- | A-, B-, AB- | B+, B-, O+, O- | B-, O- |
AB+ |
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A+, A-, B+, B-, AB+ AB- | A+, A-, B+, B-, AB+ AB- | A+, A-, B+, B- | A+, A-, B+, B- |
AB- |
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A-, B-, AB- | A+, A-, B+, B- | A-, B- |
O+ |
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O+, O- | O+, O- |
O- |
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O- |
| Parents' Blood Types | A+ |
A- |
B+ |
B- |
AB+ |
AB- |
O+ |
O- |
|---|---|---|---|---|---|---|---|---|
A+ |
B+, B-, AB+, AB- | B+, B-, AB+, AB- | NONE | NONE | O+, O- | O+, O- | B+, B-, AB+, AB- | B+, B-, AB+, AB- |
A- |
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A+, B+, B-, AB+, AB-, O+ | NONE | A+, B+, AB+, O+ | O+, O- | A+, B+, AB+, O+, O- | B+, B-, AB+, AB- | A+, B+, B-, AB+, AB-, O+ |
B+ |
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A+, A-, AB+, AB- | A+, A-, AB+, AB- | O+, O- | O+, O- | A+, A-, AB+, AB- | A+, A-, AB+, AB- |
B- |
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A+, A-, B+ AB+, AB- O+ | O+, O- | A+, B+-, AB+, O+, O- | A+, A-, AB+, AB- | A+, A-, B+, AB+, AB-, O+ |
AB+ |
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O+, O- | O+, O- | AB+, AB-, O+, O- | AB+, AB-, O+, O- |
AB- |
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A+, B+, AB+ O+, O- | AB+, AB-, O+, O- | A+, B+, AB+, AB-, O+, O- |
O+ |
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A+, A-, B+, B-, AB+, AB- | A+, A-, B+, B-, AB+, AB- |
O- |
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A+, A-, B+, B-, AB+, AB-, O+ |