Inheritance patterns of blood groups

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► ABO inheritance patterns

► Rhesus inheritance patterns

Blood groups are inherited from our parents in the same way as other genetic traits (eg, eye colour). ABO and Rhesus are the most well-known among the blood group systems.

ABO inheritance patterns

The ABO blood group system is determined by the ABO gene, which is found on chromosome 9. The four ABO blood groups, A, B, AB and O, arise from inheriting one or more of the alternative forms of this gene (or alleles) namely A, B or O.

Genetic Combinations of ABO Blood Groups

Blood group

Possible genes


AA or AO


BB or BO





The A and B alleles are codominant so both A and B antigens will be expressed on the red cells whenever either allele is present. O alleles do not produce either A or B antigens, thus, are sometimes called ‘silent' alleles.

ABO Inheritance Patterns

Parental blood groups

Child's blood group

O and O


O and A

O or A

O and B

O or B

O and AB

A or B

A and A

A or O

A and B

O or A or B or AB

A and AB

A or B or AB

B and B

O or B

B and AB

B or A or AB

AB and AB

A or B or AB

Note: These are various possible blood groups that children may inherit according to the combination of parental blood groups.

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Rhesus inheritance patterns

The Rh blood group system is attributable to two genes, RHD and RHCE, which are located on chromosome 1.

Rh positivity or Rh negativity is distinguished by testing for the RhD antigen, the expression of which depends upon whether an RHD gene has been inherited from one or both parents.

The RHD gene is dominant so a person is considered to be RhD positive whenever this gene is present, even though the gene may have been inherited from one parent. Conversely, a person will be RhD negative if no RHD gene is inherited.

Rhesus Inheritance Patterns

Parental Rh type

Child's Rh type

Positive and Positive

Positive or Negative

Positive and Negative

Positive or Negative

Negative and Negative


Note: These are the various possible Rh types that children may express according to the combination of parental Rh phenotypes

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