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.
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