Genes are always in pairs and overall expression depends whether dominant, recessive or X-linked. So there is no problem when one of the genes is abnormal e.g. AS, AC. This is called a carrier state (sickle cell trait).
Only when the two are abnormal then there is a great problem.


Genotype Compatibility






The genotypes in humans are AA, AS, AC, SS.


I hadn't heard of the genotype AC until I was researching
for this article and found Dr. Ademola Peter's article on
the subject of genotypes and blood groups. He's also the
one I quoted above and throughout this article.
Unfortunately is website is currently not accessible so I
can't provide link to the actual article.


Anyway, I guess AC is not common in genotypes or I've
simply not heard about it. But AS and AC are both
abnormal take note.


And the great problem referred to above that we're trying
to avoid with genotype matchmaking for intending
couples is the Sickle cell disease.


Sickle cell disease (a recessive disorder) is a very serious
medical condition with high prevalence rate in sub
Saharan Africa. Intending couples must make sure to
know their genotypes and be sure it's compatible for
marriage before going ahead to get married.






So who can you marry and who shouldn't you marry
based on Genotype compatibility?


Someone with the genotype AA can marry across. That is
there's no risk of having a sicklier for a child even when
he or she marries an SS. But AA marrying an SS can only
result in AS children. There's no hope of having a child
with the genotype AA. But there's no danger either.


Someone with the genotype AS should only marry
someone with the genotype AA because if AS marries AS
there's one out of 4 chances (AS, AS, AA and SS) that they
will have a child with the sickle cell disease. Same applies
when AC is combined. AC and AS combine will produce
AA, AS, AC, SC, the sickle cell disease will be SC.
Remember what the quote above from Dr. Peter said, it's
only when two abnormal marry that there is a great
problem.


Of course there are many cases where two abnormal was
combined that is an AS and AS or AC and AC or AC and AS
couples and had up to five or six children without a
single sicklier among them. But why risk it? What if you're
not so lucky? Can you forgive yourself when you end up
having a child with the sickle cell disease and put the
child through the agony the disease brings when you
could have easily avoided it?


Compatible genotypes for marriage are:
AA marries an AA. That's the best compatible. That way
you save your future children from having to worry about
genotype compatibility in future.

AA marries an AS. You'll end up with kids with AA and AS
which is good. But sometimes if you're not lucky all the
kids will be AS. Like my elder sister who is AA and
married an AS and was expecting to have kids with
genotype mostly AA. But the last I heard two out of her 3
kids are AS; I'm not sure what the genotype of her third
child is. Like I've said there's no problem having kids with
AS except if eventually the kids marry people with the
genotype AS.

AS and AS should not marry.

AS and SS shouldn't think of marrying.

And definitely SS and SS must not marry since there's
absolutely no chance of escaping having a child with the
sickle cell disease.




Blood Group Compatibility



It is advisable that intending couples should know their
blood groups before marriage. The blood groups are
designated by the letters O, A, B, AB. Blood groups have a
hereditary basis and depend upon a series of alternative
genes, a fact sometimes utilized in solving the problems
of disputed parentage.

Equally important and linked to the blood group is the
Rhesus antigen, which is positive in 83% of the British
population but about 95% among the black population.

Thus one can be O Rhesus positive (O+ve) or O Rhesus
negative (O-ve). When an Rh +ve blood is given to an Rh -
ve person, then Rhesus antibodies are stimulated; for
instance, immunization of a woman can result from
blood transfusion or injection of Rh positive blood. In
women, also, immunization due to pregnancy can result
from the passage of the Rh +ve antigen from a Rh
positive fetus across the placenta into the circulation of a
Rh negative woman.

It must be emphasized that when an Rh-ve woman is
married to an Rh positive man, the chance for her
becoming sensitized to the Rh antigen and thus having
children affected with haemolytic (red cell breakdown)
disease of the new-born is relatively small. The risk of
developing antibodies increases with succeeding
pregnancies, thus if a Rh-ve woman marries a Rh +ve
man, there is 1 in 143 chance of Rhesus iso-
immunization during the first pregnancy, 1 in 14 during
the 2nd and 3rd; 1 in 12 during the 4th, and 1 in 8 during
the 5th pregnancy.

The overall incidence of haemolytic disease of the
newborn due to this problem is about 1 in 200 of all
pregnancies. Usually, sensitization due to pregnancy
practically never results in haemolytic disease in the first
child; on the other hand, sensitization due to previous
blood transfusion may cause the first child to be affected.
Thus the importance of avoiding the transfusion of Rh
+ve blood to a Rh -ve person must be emphasized.

In conclusion, in view of the low risk of Rhesus iso-
immunization, Rhesus factor does not constitute an
absolute contraindication why a Rh -ve woman should
not marry a Rh +ve man. Even in the few cases where
sensitization occurs, the affected child can still be
effectively treated. There is a drug that can be used to
prevent sensitization if the Rhesus status of the couple is
known initially. There is no risk of Rhesus iso-
immunization if both couple are Rhesus +ve, or are
Rhesus -ve, or if a Rh -ve man marries a Rh +ve woman.

I'll conclude this article with Dr. Peter's final advice on
the matter...

Know your blood group and genotype.
Help in preventing genetic diseases by marrying a
partner of compatible genotype.
Determine the Rhesus status of every newly-born
child.



By: Olawale David Oyinlade