HOW IS YOU BLOOD GROUP DETERMINED?

We inherit our blood group genes from our parents, meaning everyone's blood group is dependent on what blood group their parents have. Your parents both have a combination of two blood group genes that determine their blood group, meaning that when you are born, you will inherit one of these genes from your mother and one from your father.

These genes we inherit can come in various forms, and it is the combination of genes you inherit that will determine your blood group. The three possible genes you can inherit that will determine your blood group are:

  • THE 'DOMINANT' GENES

    As for all genes we inherit, some are more dominant than others. In this case, the group A and B genes are classed as dominant, meaning that if you inherit either (or both) of these genes from your parents, they will always be expressed.

  • THE 'RECESSIVE' GENE

    The group O gene is classed as recessive. This means it is only expressed if you inherit one group O gene from your mother and one from your father. If the A or B gene is inherited along with the group O gene, its function will be suppressed.

The 6 possible combinations of blood group genes you can have are:

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If you inherit the A gene from your mother and the A gene from your father, you will be blood group A:

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If you inherit the A gene from your mother and the O gene from your father, or vice versa, you will still be blood group A:

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If you inherit the B gene from your mother and the B gene from your father, you will be blood group B:

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If you inherit the B gene from your mother and the O gene from your father, or vice versa, you will still be blood group B:

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If you inherit the A gene from your mother and the B gene from your father, or vice versa, you will be blood group AB:

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If you inherit the O gene from your mother and the O gene from your father, you will be blood group O:

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Therefore, if your mother or father are blood group A or B, it is possible they also have the group O gene and could pass this on to their children. The table below shows all of the possible blood groups children can have depending on what their parent's blood group is:

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So, if you know your blood group but not your parents, you may be able to narrow down which blood group they have. Also, if you and your partner both know your blood group, you can work out which possible blood groups your children will have!