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Name: Nicole
Status: Student
Grade:  9-12
Location: MA
Country: United States
Date: December 2006


Question:
Humans are almost identical in the protein-coding sections of the genome, yet each individual has a unique DNA fingerprint. How is this possible?



Replies:
The statement that the DNA from different humans is not entirely accurate. On average, one in a thousand base pairs are different when comparing two individuals, but since there are approximately 6 billion base pairs worth of DNA in a human cell, this means there are 0.001 x 6 billion = 6 million base pair differences between any two individuals. Most of these differences occur in non-essential genes or junk DNA. The genes examined to compare two individuals are non-essential genes where mutations have no effect on the individual. The genes that are analyzed to test for paternity and forensic evidence are genes where many tandem duplications or deletions have occurred. No two individuals will have the same number of gene copies when 13 CODIS markers (allele pairs) are examined.

Ron Baker, Ph.D.


Because only about 1% of your DNA codes for protein. The other 99% is known as non-coding DNA. Even though only 0.1% of your total DNA is different than any other human, that is 0.1% of 3 billion bases. This means there are about 3 million DNA letter differences between any two humans. DNA Profiles are done from areas where humans are known to be variable in their DNA. They then determine the probability that any two people would share the same DNA in that area. There are 13 areas that are tested and the probability that any two people would share the same total profile is the product of the 13 separate probabilities. This turns out to be an infinitesimally small number.

vanhoeck



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