Understanding Blood Type Inheritance

Blood type inheritance is a classic example of Mendelian genetics in humans. The way your blood type is determined depends on the specific alleles you inherit from your biological parents. This calculator uses the ABO blood group system and the Rhesus (Rh) factor system to determine the statistical likelihood of a child's blood type.

What is the ABO Blood Group System?

The ABO system is based on the presence or absence of specific antigens (A and B) on the surface of red blood cells. There are three primary alleles involved:

1. A Allele: Codominant
2. B Allele: Codominant
3. O Allele: Recessive

Because we inherit one allele from each parent, we have six possible genotypes (AA, AO, BB, BO, AB, OO), which result in four distinct phenotypes (blood types):

• Type A: Genotype AA or AO
• Type B: Genotype BB or BO
• Type AB: Genotype AB (Both A and B are expressed)
• Type O: Genotype OO (Neither A nor B are expressed)

The Rh Factor

The Rh factor (Rhesus factor) is an inherited protein found on the surface of red blood cells. If your blood has the protein, you're Rh positive (+). If your blood lacks the protein, you're Rh negative (-).

In genetic terms, the positive factor is dominant, while the negative factor is recessive.

• Rh Positive (+): Genotype ++ or +-
• Rh Negative (-): Genotype --

The Inheritance Formula

The probability of a child's blood type is calculated by crossing the possible genotypes of the parents. Since a parent with Type A could be either AA or AO, the calculator considers all mathematical possibilities:

$P(\text{Phenotype}_c) = \sum_{G_m, G_f} P(G_m) \times P(G_f) \times P(\text{Phenotype}_c | G_m, G_f)$

Where:

• $G_m$ is the genotype of the mother.
• $G_f$ is the genotype of the father.
• $P(\text{Phenotype}_c)$ is the probability of the child having a specific blood type.

How to Use This Calculator

1. Select Mother's Blood Type: Choose from A, B, AB, or O.
2. Select Mother's Rh Factor: Choose positive (+) or negative (-).
3. Select Father's Blood Type: Choose from A, B, AB, or O.
4. Select Father's Rh Factor: Choose positive (+) or negative (-).
5. Review Results: The calculator will display a breakdown of the percentage likelihood for each possible blood type and Rh factor.

Worked Examples

Example 1: Type O Mother and Type AB Father

• Mother Genotype: OO
• Father Genotype: AB
• Possible Crosses: O+A (AO) and O+B (BO).
• Result: 50% Type A, 50% Type B. Type O and Type AB are impossible.

Example 2: Type A (AO) Mother and Type B (BO) Father

• Crosses:
  • A + B = AB
  • A + O = AO (Type A)
  • O + B = BO (Type B)
  • O + O = OO (Type O)
• Result: 25% AB, 25% A, 25% B, 25% O.

Reference Table: ABO Inheritance

| Parent 1 | Parent 2 | Possible Child Blood Types | | :------- | :------- | :------------------------- | | O | O | O | | O | A | O, A | | O | B | O, B | | O | AB | A, B | | A | A | A, O | | A | B | A, B, AB, O | | B | B | B, O | | AB | AB | A, B, AB |

FAQ

Can two Rh-positive parents have an Rh-negative child?

Yes. If both parents are heterozygous (carrying one positive and one negative allele, i.e., +-), there is a 25% chance the child will inherit the negative allele from both, resulting in an Rh-negative (--) blood type.

Is it possible for an AB parent to have an O child?

Under standard Mendelian genetics, no. An AB parent can only pass on an A or a B allele. An O child requires an O allele from both parents. However, extremely rare conditions like the "Bombay Phenotype" can cause exceptions.

What is Rh Incompatibility?

Rh incompatibility occurs when an Rh-negative mother is pregnant with an Rh-positive baby. The mother's immune system may produce antibodies against the baby's red blood cells. This is usually managed with a RhoGAM injection.

Which blood type is the "Universal Donor"?

Type O-negative (O-) is considered the universal donor because it lacks A, B, and Rh antigens, meaning it can be transfused into patients of any blood type in emergencies.

Can blood types change over time?

Generally, no. Your blood type is determined by your DNA at conception. However, in very rare cases such as bone marrow transplants, a person's blood type may change to match the donor's.

Limitations

This calculator is for educational purposes and is based on common genetic models. Rare genetic mutations, chimerism, or the Bombay Phenotype can result in blood types that do not follow these standard rules. Always consult a medical professional for clinical blood testing.