Guy
I don't know why you think you have to test the entire population of the world to draw conclusions from DNA testing. There is a huge body of scientific literature from which we now understand the processes of DNA inheritance. We know that a child receives half of his or her DNA from each parent and that they receive one set of 22 autosomal chromosomes from the mother and another set of 22 autosomal chromosomes from the father. A male will have an X and a Y chromosome. A female will have two X chromosomes. We know that a child shares around 25% of his or her DNA with his grandparents, and around 12.5% of his her DNA with his great-grandparents. This is basic biology. We can use this knowledge to deduce relationships. If you and your father take a DNA test with enough markers and you share the expected amount of DNA with him and you have inherited a complete set of 23 chromosomes from him then we know for sure that he is your father.
I did not say that.
I did say that to claim everyone's DNA was different everyone in the world would have to be tested.
That stands to reason because if the final person has a DNA match with another person then everyone in the world would not have different DNA.
However you stated
Quote from: DevonCruwys on Today at 15:04:10
"Over three million people have now taken DNA tests for genetic genealogy purposes. There are thousands and thousands of related individuals in the databases mother/father/child trios, father/son pairs, first cousins, second cousins, etc. If this phenomenon were common we would have heard of it by now."
You were inferring that based on the numbers of people tested chimerism was not common. That claim cannot be made as the numbers of people tested is so small as to be insignificant.
You are talking about the equivalent of one city in a country, it could be that in a particular area or a particular group of people chimerism is not only common but the normal state of affairs.
Until more people are tested and indeed until more people have tests from different parts of their bodies that claim cannot be substantiated.
In the example I gave if the woman concerned had DNA from a cervical smear in the first place instead of from blood samples it may not have been discovered she had two sets of DNA in her body.
Take for instance tossing a coin there is a 50 percent chance of a head or a tail being shown.
I tossed a coin 10 times (not a significant number of times).
It fell heads up 7 times and tails up 3 times.
More interestingly the first 5 times in a row it fell heads up.
If I repeated that I would probably get a completely different set of results.
If however I tossed the coin say a thousand times I would expect to find the number of heads would equal or nearly equal the number of tails.
One cannot draw positive conclusions from small samples.
The mechanics of the sampling has to be taken into consideration as well.
I remember in a physics lesson at school our teacher was trying to demonstrate Newton’s Third Law of Motion. (For every action, there is an equal and opposite reaction). He was using a small cart with a sprung captive bolt in it.
The claim was that if he hit the trigger (a round ball on a vertical shaft) the cart would not move in any direction, however every time he did it moved to the right.
Was Newton wrong no, the teacher was applying an additional force to the cart because he was hitting the trigger at a slight angle rather than vertically.
Cheers
Guy
