Inheritance of Haemoglobin

Genes always come in pairs; a person inherits one from their mother and one from their father, every individual inherits two haemoglobin genes.

Each parent is born with two haemoglobins. Each time a couple is expecting a child, only one haemoglobin is inherited from each parent, in order for the child to make his or her own two haemoglobins. In EACH pregnancy, there are always FOUR possible combinations the child can take. These are known as CHANCES.

Example 1

If both parents have the normal haemoglobin combination (Hb AA) gene combination, each time that they are expecting a child the child will inherit one of four possible combinations, as illustrated below:


In this example there is a 100% chance that ALL of this couple’s children will inherit normal haemoglobin (Hb AA) gene combinations.

Example 2

If one parent has normal haemoglobin (Hb AA) and the other parent is a carrier (trait) (Hb A + one unusual haemoglobin) gene combination, each time they are expecting a child the child will inherit one of four possible combinations as illustrated below:


In this example there is a 50% chance that their child will inherit the normal haemoglobin gene combination (Hb AA) and a 50% chance that their child will inherit a carrier (Hb A + one unusual haemoglobin) gene combination.

Example 3

If both parents are carriers (trait) (Hb A + one unusual haemoglobin) gene combination, each time that they are expecting a child the child will inherit one of four possible combinations as illustrated below:


In this example there is a 25% chance that their child will inherit the normal haemoglobin gene combination (Hb AA), a 50% chance that their child will inherit a carrier (trait) (Hb A + one unusual haemoglobin) gene combination and a 25% chance that their child will inherit a disease (Hb two unusual haemoglobin) gene combination.

Depending on the type of unusual haemoglobin gene that the child has inherited the disease state can be clinically insignificant, mildly, moderately or seriously severe.

Example 4

If one parent has normal haemoglobin (Hb AA) and other has a disease (Hb two unusual haemoglobin) gene combination, each time that they are expecting a child the child will inherit one of four possible combinations as illustrated below:


In this example there is a 100% chance that their child will inherit a carrier (Hb A + one unusual haemoglobin) gene combination.

Example 5

If one parent is a carrier (trait) (Hb A + one unusual haemoglobin) and the other parent has a disease state (Hb two unusual haemoglobin) gene combination, each time that they are expecting a child the child will inherit one of four possible combinations as illustrated below:


There is a 50% chance that their children will inherit a carrier (Hb A + one unusual haemoglobin) gene combination and a 50% chance that their children will inherit a disease (Hb two unusual haemoglobin) gene combination.

The Family Connection

Once an unusual haemoglobin gene has been found in one family member it is important to be aware that other members of the same family may also have the unusual haemoglobin gene. Therefore, it is important to share the information with other family members especially with those who are of child bearing age, planning to get married, start a family or have more children - brother, sisters, aunts, uncles, cousins.

Its is advisable for other members of the family to be made aware that the unusual haemoglobin has been found in the family; this is most important for those planning to get married or starting a family.