Ever wonder if your family is somewhere out there but not the one you see everyday (most of the time)? I do when I was young, not because of bad childhood but the wrong teaching from TV that says children are sent by birds to front door, crack open from rocks (sun wu kong) or even from the trash bin.
Song Ci (宋慈), a coroner that wrote the first book for forensics in the world - "Collected Cases of Injustice Rectified" (洗冤集录), there is a paragraph in there that talked about inspection of bone to identify the family. If person A is the parent and his/her bones are still there. Person B comes to identify if he/she is the biological son/daughter of the dead, how to test? Try to make person B to drip one or two drops of blood on the bone, if it is the parent, the blood will seeps into it, otherwise it will not seep in. (the actual text from 洗冤集录: 检滴骨亲法，谓如某甲是父或母，有骸骨在，某乙来认亲生男或女，何以验之？试令某乙就身刺一两点血滴骸骨上，是的生亲则血沁入骨内，否则不入。俗云“滴骨亲”盖谓此也。)
There is another more well-known method in Hong Kong drama, the inspection of blood to identify the family (滴血认亲), also called blood merging method (“合血”法). The 2 person drip a drop of blood into a container, if the 2 droplets merge, then they are relatives, vice versa. However, salt and vinegar can cause the blood droplets to merge, and create confusion and fraud. (今各刺出血滴一器内，真则共凝为一，否则不凝。但生血见盐醋则无不凝者。故有以盐醋先擦器皿，做奸蒙混。)
The question is... how true is the methods in term of science?
For the inspection of bones, as long as the bones are dry, it can easily absorb any liquid into it. So, no matter if there's any relationship in blood, this method failed to clarify anything but the absorption power of bones.
For the inspection of blood, it is actually not true as well. Basically, human have 4 types of blood group, namely A, B, O and AB. Each of us will have 23 pairs of chromosome, and we get 1 of each pair from mum and dad. Blood group is also contributed by parents. If mum gives allele A to a child and dad gives allele B to a child, the child will have 1 A and 1 B allele and that makes him/her blood group to be AB. The allele of A and B is codominance, which means that allele A and B can be expressed fully if exist in the gene. If one of the parent give O allele, and the other gives A or B allele, the child will have A group or B group instead of O group or AB group.
Hence, A + B = AB, A + O = A, A + A = A, B + O = B, B + B = B, O + O = O
In case of blood donation, it is the antibody in the blood that determines the acceptance of transfusion.
People with AB blood group (universal acceptor) have A and B antigens on the surface of their red blood cells, and their blood serum does not contain any antibodies acting against A or B antigen (otherwise, the antibody is attacking own cells right?) Thus, AB group individual can get blood transfusion from any group (wont reject any blood transfusion due to no antibody that act against A or B antigen) but can only donate to another AB blood group individual.
People with blood group A will have A antigen on the surface of their red blood cells and blood serum have antibodies that act against B antigen. Thus, he/she can receive blood from A or O and donate to A and AB blood group individual.
People with blood group B will have B antigen on the surface of their red blood cells and blood serum have antibodies that act against A antigen. Thus, he/she can receive blood from B or O and donate to B and AB blood group individual.
People with blood group O (universal donor) do not have A or B antigens on the surface of their red blood cells but their serum contains antibodies that act against A and B blood group antigens. Thus, he/she can only receive blood from O group donor and can donate blood to any blood group.
Okay, back to the question. Why do some blood merges and some do not? This is because the 2 drops of blood have same blood group or no antibody that act against the blood, it got nothing to do with relationship, maybe a little but not precise.
Let me give you 2 examples. The first one is not related but the test show they are related. "Father" with O blood group and "daughter" with O blood group. Their blood will merge but they are not family related. Although they share the same blood group, there are also many people out there that have O blood group. Thus, they can only tell that they "maybe" related but it cannot be confirm with blood test like this. This test maybe true at some point, but it is not accurate.
The second one is they are related but the test show they are not. "Mother" with AB blood group and "son" with A blood group. "Mother" with AB blood group will contribute A or B allele to her son, and in this case, the mother contributed A allele to her son and the father contributed A or O allele (because in order to get A blood group, there are 3 possibilities: A + A or A + O or O + A). Since they do not share the same blood group, blood serum from son (with antibody that act against B antigen) will attack the blood of mother with A and B antigen on red blood cells. Thus, even though they are related, the test failed to prove it right.
Just one last thing for your knowledge, if you have O blood group and any of your parents is AB blood group, he/she is not your mum or dad. If you have AB blood group and none of your parent is AB group, dont worry, he/she is (might be) your mum/dad. =P
A list for you to check~
AB + AB = A or B or AB
AB + O = A or B
AB + A = A or AB
AB + B = B or AB
A + A = A or O
A + B = A or B or AB or O
A + O = A
B + B = B or O
B + O = B
O + O = O
Hope you learn some new things today! =D happy 2010~ =)
Oh yeah! dont forget to tell me your blood group! i am curious! =P and mine? I am A group~ and my mum used to tell me I am XO blood group... =.="""
Until next time~ ^_^ / See ya! =D
