My father is AB and my mother is A. And guess what?! I'm O! So I thought maybe the test just went wrong. But then, the opporuinity came of a certain experiment in school involving blood typing. So, I tested my own blood. I placed the Anti-A on one drop of my blood and I kept telling the drop of blood to agglutinate! agglutinate! I'm A! I'm A!. But then it didn't. I really wanted to be A coz all my other siblings are A. Being O just doesn't make me belong. There was also no agglutination when I dropped the Anti-B either. And that had made me conclude myself that I was indeed type O; mysteriously O. It's nearly impossible for two AB parents to have a child with blood type O. But in very rare cases it can happen if one parent has a cis-AB gene. The genes for the ABO blood-type system are located on chromosome 9. Everyone has two copies of each gene, one from their mother and one from their father. The “A” gene makes an enzyme which can put a sugar called 'N-acetyl-N-galactosamine' on red blood cells - we'll just call it the “A” sugar. The “B” gene makes an enzyme which puts a different sugar “D-galactose” on red blood cells; we'll call it the “B” sugar. The “O” gene makes an enzyme that doesn't put any sugars at all on the red cell. People have type “A” blood if they only have the “A” sugar on their red cells. So people with blood type “A” either have one chromosome 9 that has the “A” gene and one chromosome 9 with the “O” gene or they have two chromosome 9s both with the “A” gene. In either case only the 'A' sugar can be put on red cells. You have type “B” blood if you only have the “B” sugar on your red cells. So people with blood type”B” either have one chromosome 9 with the “B” gene and one with the “O” gene or they have two chromosome 9s both with the “B” gene. Again, in either case only the “B” sugar can be found on their red blood cells. Type 'O' people have neither the 'A' nor the 'B' sugar on their red cells. So they usually have two chromosome 9s both with the “O” gene. (Note: in rare cases you can have a condition in which the enzyme that makes the sugars is present but the hook where the sugars are supposed to be attached isn't made: this is called O-Bombay and is another story.) Type “AB” people have both “A” and “B” sugars on their red cells. In 99.999% of cases this is because they have one chromosome 9 with an “A” gene and one with a “B” gene. So most of the time when a type “O” person and a type “AB” individual have children half are “A” and half are “B” depending upon whether they get the chromosome 9 with the “A” or the “B” gene from their type “AB” parent. There is, however, the quite rare “cis-AB” gene in which one chromosome 9 either makes BOTH the “A” and “B” enzymes or makes an enzyme which can put BOTH the “A” and “B” sugars on red blood cells. If you have a “cis-AB” gene on one chromosome 9 you could have a “O” gene on the other chromosome 9 and have type “AB” blood since the “cis-AB” gene product could put both “A” and “B” sugars on your red cells. In this case if you were to have children with a type “O” person (who would have two chromosome 9s each with an “O”gene) - one-half of your offspring would be type “AB” and one-half type “O” depending upon whether they got your chromosome 9 with the “cis-AB gene” or the one with the “O” gene. So a type “AB” and a type “O” person can have type “O” or type “AB” children if the type “AB” person has the rare “cis-AB” gene. And theoretically two “cis-AB” people -- each with one chromosome 9 with the cis-AB gene and one with the O gene -- could have children one-fourth of whom would get the “O” gene from each parent and thus be type “O”. There are also many other interesting combinations related to not being able to make the hook where the sugars are attached to the red cells so you could have the “A” gene or the “B” gene and still not be able to put the “A” or the “B” sugars on your red cells. (O-Bombay). The moral of this story is that the ABO/ABH system is actually complex. Web sites that say that certain children are “impossible” are wrong and may lead people to unjustifiably question their paternity.
I don't think I'm adopted but I didn't know any explanation for this also. Until one day, I happened to have the courage to ask my teacher who's an expert in blood reagrding this matter. She said my father could've been cis-AB. I was boggled by this so I also consulted a friend of mine - Google.
a complicated explanation comes from http://www.annclinlabsci.org/cgi/content/abstract/34/4/437 which says: The cis-AB is a very rare phenotype in the ABO blood group system. It corresponds to a special ABO allele encoding a glycosyltransferase that is capable of synthesizing both A and B antigens. Until now, gene sequences of only 3 cis-AB alleles were characterized. One was the A1v allele with a nucleotide substitution G803C at codon 268; the second was the B allele with a nucleotide substitution A796C at codon 266; and the third arose from a point mutation C700T at codon 234 in exon 7 of the B transferase gene. In this study, we found a novel cis-AB allele when performing paternity tests in Chang Gung Memorial Hospital in Taiwan. Although his father was O blood type, a serologically AB blood type child was confirmed as being his father’s offspring on the basis of 16 microsatellite markers (99.97% plausibility for the child and father). Exons 6 and 7 of the child’s ABO alleles were characterized by direct sequencing and gene cloning. The results showed that the child has one O1 allele and the second allele is almost identical to A1*02 allele except for a single point mutation at nucleotide position 796, where an A replaces a C and leads to a change of leucine to methionine at amino acid 266. This implies that the child’s O1 allele was inherited from his father and the other allele was inherited from his mother. In conclusion, the novel cis-AB allele reported here is derived from the A transferase gene through a nucleotide substitution C796A, which differs from the 3 previously reported cis-AB alleles.
This just made my head spin more so I sought another explanation and I found a more simpler one from http://www.science.ca/askascientist/viewquestion.php?qID=595.Hahaha...I'm one of these "interesting combinations". In a way this makes me feel special. My acquisition of my blood type was in a rare possibility. So cooooll...
So that means, my mother is heterogeneous A and my father is cis AB. I'm reallly not adopted!! haha...It would be interesting to have 2 sets of parents though...Just kidding!
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