How accurate was blood typing in determining parentage back in the day? And from what I understand, blood types represent contributions from both parents, so how are there so few different human blood group systems (Wiki says there are 30)? And if there are only 30 different possibilities, would there be a high chance of false positives?
Say some guy showed up and my door and said “Hi, I’m Swallowed My WalkieTalkie!”, would a blood test have been able to determine if we are half-brothers?
My understanding was that it was more of a “rule it out” sort of thing - in other words, if your parents are both A+ and so are you, it doesn’t say much, but if they’re both A types and you’re an AB something is not quite right.
All “normal” blood types are A, B, AB, and O.
Genetically, this is as follows:
AA, AO, OA
BB, BO, OB
AB, or BA
and OO
and these come in Rh + or -.
There are, however, some rare mutant blood types.
Blood typing for heridity can be usefuol, because the genetic sequence can be different. Parents with AO and AO blood type can give any combination of A or O blood typing.
This means that they can only give AA, AO, OA (which is the same as Ao functionally) or OO blood. So if the child has B anywhere, then we know it cannot be born from those two parents.
As a matter of fact, it is rare but two type A parents could, in principle, have a type AB or even type B child. The reason is that it takes several steps to manufacture the type B antigen and if it just so happened that one of those steps was blocked by the lack of some enzyme in one parent and a different step blocked by the the absence of a different enzyme in the other parent, the child could (and occasionally does) have all the apparatus to make the B antigen. So even the negative inference one can draw from blood typing is not 100% (although it could be considered as beyond reasonable doubt).
The only absolutes are that an AB person could not produce an O child and vice versa, and that the child of two ABs could not produce an O and vice versa.
So pre-DNA testing if a half-sibling turned up, say to contest a will or something, and the parents were all dead, there was no really reliable way of determining whether or not he/she was really a half-sibling?
Correct me if I’m wrong, DNA could conclusively identify half-siblings, right?
If the shared parent is the mother, a mitochondrial DNA test would do. Establishing a link through a common father is much trickier.
This reminds me of an interesting story I heard by way of my sister while she was in med school. I can’t really say if it’s true or not, so take it FWIW.
The story goes that a woman’s son needs a transplant of some kind - kidney, I think. She and her husband both volunteer to be a candidate donor, and the hospital runs the usually battery of organ compatibility tests. In the process, they discover something strange. The son’s blood type would be an impossible outcome for the mother’s genotype.
Now, the woman is dead sure that she gave birth to her son, so they immediately suspect that some kind of switched-at-birth accident happened. They run a full-blown genetic paternity and maternity test, and come up with completely bizarre results. To some ridiculous probability, the husband was definitely the boy’s father. But the maternity results were inconclusive - they shared a lot of genetic markers, but not as many as a mother and son normally ought to.
They decide to re-run the tests to be sure that there wasn’t some kind of fluke, but they keep getting the same answer. Eventually someone gets the idea to run the tests again, but to use a skin tissue sample instead of a saliva swab like they used before. This time the test comes back conclusively establishing maternity.
Eventually they put 2 and 2 together and figure out that this is woman was an extremely rare case of human chimerism. Basically, two fraternal twins somehow merged in utero, creating a rare, viable embryo that exhibits genetic mosaicism. So the cells comprising at least one of her ovaries came from one line of cells while the initial samples they took for genetic testing happened to come from the other line. Her red blood cell factories also apparently came from the other line. When they finally took a tissue sample from some other part of her body, they got ahold of a patch of cells from the same line as her ovary(ies).
Mosaicism is very rare, but when it does occur, it may be suspected because the individual might have two different eye colors, or skin tones, or hair color in different areas of their body. But in a few cases, the phenotype of the different cell lines is so similar that there’s no discernible difference between tissues consisting of cells from different lines. It may go completely undiscovered unless something like this crops up where genetic testing is performed.
In the most famous Switched At Birth cash, the Twiggs, who both had type O blood, found out that their daugher Arlene had type B blood and could not be their daughter two years before she died, yet they only sought out their biological daughter after she died.
I don’t blame Robert Mays for not want to deal with the Twiggs after they denied him the opportunity to know his biological daughter before she died.
There is more to parentage testing than the ABO blood group system. In the past, the ABO, Rh, MNSs, Kell, Duffy and Kidd blood group systems have been used to determine parentage. Parentage testing based on these techniques were used for a very long time and pitfalls in interpretation are well known. Having said that, they are no longer in use. Pretty much everyone now uses molecular techniques to look at DNA polymorphisms.
Nunavut Boy, Lab Bitch
Forgot the ‘how accurate’ part:
According to my textbook, in an ideal world using all the classic genetic systems (which includes the ABO, Rh, MNSs, Kell, Duffy and Kidd blood group systems previously mentioned, plus subtyping of RBC enzymes, serum proteins and immunoglobulins as well as HLA A and B loci antigen detection), a lab can be up to 99% sure of paternity, given access to the mom, child and purported father. Getting this 99% depends on a lot of statistical calculations and access to phenotype frequency charts corresponding to the ancestry of the people being tested.
The story **Stathol **tells (I don’t want to quote it all) was on TV, I think on the Discovery channel. There were actually two cases presented. In the maternity case, the woman later went on to have another child, and this time they took a sample of the newborn’s blood immediately and sure enough it was not a match to its mother’s blood DNA.
In yhe late 60’s my brother and his wife were suing each other for divorce.
Her clame mental cruility, she claimed that some times my brother claimed the daughter was not his.
My brother’s lawyer called for a blood test. It could not prove the daughter was his, but it could prove she was not. Turned out she could not be.
According to the lab they had only 2 cases proven not the father.
Interesting. So if someone claimed to be my half-brother, would there be any reliable way of proving it was so? What if the guy needed one of my kidneys or something?
Nobody can make you give up a kidney, and if you wanted to donate it, doctors would probably just test you for compatibility rather than to see if you’re siblings.
If the fellow was saying you had the same mom, your mitochondrial DNA ought to be the same, as Bryan Ekers said.
If he’s saying you share the same father, and you’re both male, you ought to have identical Y chromosomes. If you’re not both male, there’s no simple shortcut like that, and you start having to test more stuff. That’s not to say that it can’t be shown reliably, just that it takes more effort.
Interesting. If the half-sibiling was female, would she be easy to compare to my sister? (So both female half-siblings with the same father.)
Two female half-siblings from the same father ought to have one identical X chromosome (and one different, that one coming from their moms), because a man has only one X chromosome, and gives it to all of his daughters. (Remember, a man has one X and one Y, and each sperm only has one of those two. If an X-bearing sperm fertilizes an egg, that makes a daughter, while a Y-bearing sperm makes a son.) The fact that each woman has two X chromosomes in all of her cells, only one of which will match her half-sister’s, probably makes this much more annoying than the other sorts of testing I mentioned.
That said, there are others here who are more familiar with this sort of genetic testing than I, who can probably give a more complete answer.
No, women get no Y chromosome from the father. So more elaborate tests would be required. It is still possible, but more complicated. In Stathol’s story it is important to note that it was the mother who was a chimera and therefore the one that they had to try a different sample from. If the child were the chimera, both sets of cells would look like they came from the mother. It is still an amazing story. Genetics is never quite so simple as it seems at first look.