“DNA fingerprinting” is a recently-introduced biochemical procedure that uses a pattern derived from a person’s genetic material to match a suspect’s genetic material against that of a specimen from a crime scene. Proponents have claimed astronomically high odds against obtaining a match by chance alone. These odds are based on an assumption that there is independence between the different characteristics represented by a single pattern.
Which one of the following, if true, casts the most doubt on the claim of the proponents of DNA fingerprinting?
(A) The large amount of genetic material that people share with all other people and with other animals is not included in the DNA fingerprinting procedure.
(B) There is a generally accepted theoretical basis for interpreting the patterns produced by the procedure.
(C) In the whole population there are various different subgroups, within each of which certain sets of genetic characteristics are shared.
(D) The skill required of laboratory technicians performing the DNA fingerprinting procedure is not extraordinary.
(E) In the investigation of certain genetic diseases, the techniques used in DNA fingerprinting have traced the transmission of the diseases among the living members of very large families.
Think of what you have to weaken here: the claim of the proponents of DNA fingerprinting. What is that claim? that odds against obtaining a match by chance alone are astronomical. Say, the odds are something like a 1 in a billion that the DNA fingerprint of one person will match the DNA fingerprint of another person.
You have to weaken this claim. The author tells you that the odds were calculated assuming that the different characteristics in a pattern are independent. Think of a password. If you have to write a 10 letter password using only letters of the alphabet, there are 26*26*26.....26 = (26)^10 different ways in which you can write it. The odds against two people creating the same password are very high. You are assuming here that each letter is independent of the other 9 letters. What if that is not the case? Say, your password must have at least 2 of the 5 vowels. You have created restrictions. Each letter is not independent of the other letters now. The number of passwords you can create now is significantly lower.
Option (C) tells you that some groups share the same characteristics i.e. of the 10 letters, 5 letters are identical in each password of this group. Now, the chances of getting the same password have increased significantly. This weakens the claim that the odds against finding a match are very high.
The only other option you could get stuck in is (A) The large amount of genetic material that people share with all other people and with other animals is not included in the DNA fingerprinting procedure.
This just tells you that the features that people share are not a part of fingerprinting procedure. This is like telling you that the passwords actually have 15 letters but the first 5 letters are the same for everyone. Basically, it doesn't change our odds at all. We anyway did not include the common part in our calculation. Hence, this option does not weaken the claim.
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