Earlier on there was a post concerning haemoglobin genotype and it was observed that there is need for some clarification. Refer to this link https://www.nairaland.com/4850814/genotype-combinations-possible-results-educate



Firstly, what we commonly refer to as “genotype” in terms of AA, AS, etc is correctly referred to as “Haemoglobin Genotype” shortly written as Hb Genotype.

Genotype is the genetic makeup of an organism. Hb genotype is the genetic makeup of the haemoglobin component of the red blood cells.

The normal hb gene is hbA. There are over a hundred abnormal hb variants including S, C, D, F, H, etc. The common ones are the S and C variants. F is found in newborns but could be found in adults and children above 9 months in some disease conditions.

Biologically, an offspring can only inherit one of the hb gene from a parent. That is, if a father is AA and the mother AS, the child can inherit one A from the father and either an A or an S from the mother resulting to either AA or AS hb genotype.
Hb genotype should not be confused with blood group which is a different subject entirely.

Possible inheritance pattern from the common hb gene A, S and C combinations (AA, AS, AC, SS, SC and CC) are as follows:
AA x AA = AA AA AA AA
AA x AS = AA AA AS AS
AA x AC = AA AA AC AC
AA x SS = AS AS AS AS
AA x SC = AS AS AC AC
AA x CC = AC AC AC AC
AS x AS = AA AS AS SS
AS x AC = AA AC AS SC
AS x SS = AS AS SS SS
AS x SC = AS AC SS SC
AS x CC = AC AC SC SC
AC x AC = AA AC AC CC
AC x SS = AS AS SC SC
AC x SC = AS AC SC CC
AC x CC = AC AC CC CC
SS x SS = SS SS SS SS
SC x SC = SS SC SC CC
SC × CC = SC SC CC CC
CC x CC = CC CC CC CC

NB: These crosslinks and possible offsprings are probability per birth. So there is a 25% probability of giving birth to any of the four possible offsprings per crosslink. So a couple who are both AS can give birth to four children and all of them will be AA or AS or SS.

The C gene is the less common of these common hb genes. It is not a recent type of hb gene. It has clinical similarities with the S gene. It can easily be confused with S gene in the laboratory, but with a proper QC in place, a Medical Laboratory Scientist can give the right result.

NB: Though hb genotype can help determine paternity to some extent, paternity testing is better done using DNA analysis. Especially in this era of growing cases of paternity fraud.

I advocate putting an end to Sickle Cell Disease (SCD) by ensuring that carriers of the SCD gene (S and C) don’t marry fellow carriers. There are different schools of thoughts to this though.

There is currently no cure to correct abnormal hb gene yet. There are gene therapy researches currently ongoing. The best form of management we have now is bone marrow transplant which could be expensive and not readily available to the ordinary citizen.