Originally posted by FZ+
I don't know whether this qualifies for kindergarten fluff or not...
The way it is done is that they extract a sample of your DNA (and the daughter's), and then replicate it many times using a process called PCR. Then, with these more reasonable amounts of DNA, they use a type of electrophoresis to separate out the components of the DNA to for a genetic "fingerprint".
The way this works is to use enzymes call restriction endonucleases to break up the DNA into certain segments, each of which leaves a specific trace with PAGE (polyacrylamide gel electrophoresis), in terms of how well they form ions, and their relative sizes. Basically, the cut segments of DNA are put on the centreline of a gel (which as a seive) and a current applied and then switched off. In that interval, the ions would migrate towards the positive or negative terminals with different speeds(due to different sizes), and hence get separated. A staining agent is used to make the pattern appear.
By cross referencing particular groups of patterns on the dna fingerprint that are know to vary across families, they can identify a genetic relation. The mother of the child is useful in sorting out which signature came from the mother and which from the father, hence sorting out anomalies.
I'm sorry FZ, I really don't think it is done that way.
Here is what happens: DNA is isolated from child and alleged father, preferentially also from the mother. The genetic fingerprint is generated by amplifying 16 polymorphic loci on the genome (16 regions that are known to vary in length from one person to another with high heterozygosity). Now: each fragment will have a different size range and is labeled with a different color. These fragments are put on a cappilary and are separated on size and detected by color.
The idea is: if the child has a state x at a loci, and the mother doesn't have that state x, the allele HAS to have come from the father. If the alleged father has state x, he MIGHT be the real father, but you are not sure.. you need the information of all the other loci. If the father DOESN'T have state x, you would think you are sure that the father CAN'T be the father. True, but these length repeats in the genome are unstable, the length can change from one generation to the other - mutate. So you still need the information of the other markers. That is why you can not reach 100% certainty, but the more loci, markers are typed, the more certain one can be.
The problem is: the technique itself is not fail-proof eather, it can happen that some loci, markers didn't amplify. An option would be to type 7 more markers and use a different technique. The first one I described is based on fluoresent detection, the second one could use silverstaining to visualize the results. If THIS didn't yield enough certainty either, they can do a 3rd test, restriction fragment length polymorphism with up to 8 markers.. I guess this is the one FZ described.. the problem with this one is that a different type of marker is used: single nucleotide polymorphism, which only has two states (compared to the other marker which has many states), less states is less information.
Important in my opinion, I don't know if it is routinely done, is to also get the same information from the mother so that it is easy to track which allele came from where in the child.
I hope this helped more than it confused you, Tribdog, at least you know that they can do these three different tests to be absolutely certain of the answer. Good luck.
