Question

If both parents are carriers of sickle cell anemia then what is the ratio of progeny?

• A. 1 normal : 2 sufferers : 1 carrier
• B. 1 normal : 2 carriers : 1 sufferer
• C. 1 normal : 3 carriors : 0 sufferer
• D. 2 normal : 0 carrier : 2 sufferer

Answer 1

Answer: (B)

1 normal : 2 carriers : 1 sufferer

Sickle Cell Anaemia is called a recessive condition because you must have two copies of the sickle haemoglobin gene to have the disorder.

If you have only one copy of the sickle haemoglobin along with one copy of the more usual haemoglobin (A or HbA) you are said to have Sickle Cell Trait. This is not an illness but means that you “carry” the gene and can pass it on to you children. If your partner also has Sickle Cell Trait or Sickle Cell Anaemia your children could get Sickle Cell Anaemia.

If both parents have sickle cell trait (HbAS) there is a one in four (25%) chance that any given child could be born with sickle cell anaemia. There is also a one in four chance that any given child could be completely unaffected. There is a one in two (50%) chance that any given child will get the sickle cell trait.

So the ratio of progeny is 1 normal : 2 carriers : 1 sufferer.

So the answer is option B '1 normal : 2 carriers : 1 sufferer'.