Yes, It Is Not Impossible. 'AA' Can Marry 'AS' And Give Birth To 'SS'

YES it is not impossible, couples that are AA/AS can give birth to SS , this is how
1. let me differentiate between haemoglobin genotype and haemoglobin phenotype
To get a particular GENOTYPE you have to do a genetic testing or use two or more of the screening test (the conventional electrophoresis that we do + HPLC or other similar test) to confirm the true genotype while hb PHENOTYPE is the appearance /characteristics of an individual haemoglobin on conventional electrophoresis which we loosely refer to as GENOTYPE
Most times when we call ourselves AA,SS,AS we are actually referring to our Haemoglogin PHENOTYPE and NOT GENOTYPE, as most of us don’t do genetic tests, all we do is haemoglobin electrophoresis
2. lets explain the concept of thalasemic trait. Thalassemias are quantitative defect of haemoglobin which means some one can be AA but the one or both A in this person is is absent otherwise known as thalassemia minor and major respectively. If such person run haemoglobin Electrophoresis( the test that we always loosely regard to as genotype) only A band will be seen and such a person will be regarded as AA. But they are also prone to anaemias and some certain abnormal features in the blood depending on the degree in the reduction in the defective A . such individuals can be Aβ-Thalassaemia(otherwise known as thalassaemic trait) if one of the’ A gene’ is normal, or β-Thalassaemia major if both are affected
3. lets merge the two concepts above and form AND SEE THE DIFFERENT PHENOTYPE THAT EXIST AND THE POSSIBLE CORRESPONDING GENOTYPE
If PHENOTYPE is AA the likely GENOTYPES will be AA , Aβ-Thalassaemia
If PHENOTYPE is SS the likely GENOTYPES will be SS, Sβ-Thalassaemia (MEANING THE OTHER ‘A’ THAT WOULD HAVE MADE THIS AN ‘AS’ IS TOTALLY ABSENT) Others might include SD,SG etc though these are very rare
If PHENOTYPE is AS the likely GENOTYPES will be SA (NOTE – ‘S’ COMES BEFORE ‘A’ BECAUSE THE A IS THALASSAEMIC, THOUGH NOT TOTALLY ABSENT AS THE ONE ABOVE ,IT IS SUSBSTANTIALLY REDUCE), or truely AS
4. Lets assume this our hypothetical couple have Hb eleterophoresis done and was told that the genotype of partner 1 is AA, and that of partner 2 is AS ,but the one that is called AA is actually Aβ-Thalassaemia as ealier mentioned. There possible offspring include
I. AA, If the child inherit the normal A from partner 1 and another normal A from partner 2
II. Aβ-Thalassaemia ,If the child inherit β-Thalassaemic A from the partner 1 and normal A from partner 2
III. AS,If the child inherit normal A from partner 1 and S from patner 2
IV. Sβ-Thalassaemia If the child inherit β-Thalassaemic A from partner 1 and S from partner 2
Note that scenario I above will show AA on Hb electrophoresis, scenario ii will show AA on electrophoresis, scenario iii will show AS on electrophoresis and scenario iv will show SS on electrophoresis
I have tried to simplify the medical terms but if you still have a doubt or clarification ask and I will try to shed more light, as much as I can.