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Do you always inherit your parents blood type?


Blood types are inherited from our parents through genetics. However, the inheritance patterns can sometimes be complex, and children do not always directly inherit either parent’s blood type. There are four main blood types (A, B, AB, and O) and two Rh factors (positive and negative). Which type you inherit depends on the specific blood types and Rh factors of each parent.

How Blood Types Are Inherited

There are two major blood group systems that determine your blood type – the ABO system and the Rh system.

ABO Blood Group System

The ABO blood group system consists of 4 blood types:

  • Type A
  • Type B
  • Type AB
  • Type O

Your ABO blood type is determined by the alleles you inherit for the ABO gene from each parent:

  • The A allele produces the A antigen on red blood cells
  • The B allele produces the B antigen
  • Type O has no antigens

Here is how the alleles combine to determine blood type:

Blood Type Genotype
A AA or AO
B BB or BO
AB AB
O OO

So you need one A or one B allele to be type A or B. You need both alleles to be type AB. And type O has no A or B alleles.

Rh Blood Group System

The Rh system consists of the following blood types:

  • Rh positive – has Rh antigen on red blood cells
  • Rh negative – does not have Rh antigen

Your Rh type is determined by the alleles you inherit for the Rh gene:

  • Rh+ allele produces Rh antigen
  • Rh- allele does not produce Rh antigen

So if you inherit at least one Rh+ allele, you will be Rh positive. You need two Rh- alleles to be Rh negative.

How Parents Pass Down Blood Type

Each parent passes down one of their two ABO alleles and one of their two Rh alleles. Here are the possibilities:

Mother’s Blood Type Mother’s Possible Alleles
A+ AO Rh+
A- AO Rh-
B+ BO Rh+
B- BO Rh-
AB+ AB Rh+
AB- AB Rh-
O+ OO Rh+
O- OO Rh-
Father’s Blood Type Father’s Possible Alleles
A+ AO Rh+
A- AO Rh-
B+ BO Rh+
B- BO Rh-
AB+ AB Rh+
AB- AB Rh-
O+ OO Rh+
O- OO Rh-

Each parent randomly passes down one of their two ABO alleles and one of their two Rh alleles to their child.

Blood Type Inheritance Patterns

Given all the possible allele combinations, here are some key facts about how blood types are inherited:

Rules for ABO Blood Types

  • Two type A parents can only have a type A or O child.
  • Two type B parents can only have a type B or O child.
  • One parent AB and one parent O can only have A, B, or O children.
  • Two type O parents can only have a type O child.
  • Parents with AB+AB, A+O, or B+O have a 50/50 chance of passing either allele.

Rules for Rh Blood Types

  • Two Rh+ parents will always have an Rh+ child.
  • If one parent is Rh+ and the other is Rh-, there is a 50/50 chance of the child being Rh+ or Rh-.
  • Two Rh- parents will always have an Rh- child.

Putting it all together, here are some examples:

Mother’s Blood Type Father’s Blood Type Possible Child Blood Types
A+ A+ A+ or O+
B- AB+ A+, B+, AB+, or O-
O+ O+ O+
A- B+ A+, B+, O+, A-, B-, O-
AB+ AB- A+, B+, AB+, or A-, B-, AB-

As you can see, the child’s blood type is not always a simple combination of the two parents’ types. There are many possibilities depending on the specific alleles passed down.

Special Cases

While the above patterns hold true in most cases, there are some rare exceptions:

ABO Bombay Phenotype

This very rare phenotype lacks the A, B, and H antigens. It can occur when a child inherits two recessive hh alleles, even if the parents have normal A, B, or O blood types.

Rh Blood Type Switch

In very rare cases, someone with an Rh- mother and Rh+ father may end up with Rh+ blood. This occurs through a process called recombination, and happens in less than 1% of Rh inheritance.

Chimerism

With chimerism, an individual has two genetically distinct cell populations derived from two different zygotes. This can happen when two fertilized eggs fuse early in development. The result is an individual with some tissues that may be one blood type, and other tissues that are a different blood type.

Conclusion

While children typically inherit an ABO allele and an Rh factor from each parent, the child’s actual blood type is not always a simple mixture of the parents’ blood types. There are specific inheritance patterns based on the interaction of the different blood group systems. In most cases, the child’s blood type will be consistent with one of the potential combinations from the parents’ blood types. But rare exceptions like the Bombay phenotype, Rh recombination, and chimerism can sometimes lead to unusual results. Overall, blood type inheritance follows a complex genetic pathway with many possible outcomes.