Probability calculations are used in forensic applications of DNA fingerprinting to determine if:

A.	DNA from two different sources have matching alleles.
B.	DNA samples were degraded before analysis.
C.	A match between alleles of different DNA samples might have occurred by chance. The frequency of the occurrence of different VNTR alleles in many different populations of racially and ethnically diverse peoples have been determined. Statistical calculations are used to estimate the frequency of a multi-locus DNA profile in the reference population. If a DNA forensic scientist determined that DNA from semen from a vaginal swab of a rape victim matched the DNA profile of a suspect at 5 different VNTR loci, and the frequency of the profile was only 1 in 27.8 million, the DNA analyst could report this number to the jury, and the jury could evaluate whether the match of DNAs might have occurred by chance.
D.	An unknown DNA sample is from a male or a female.
E.	Alleles in the suspect's DNA are different from alleles of a victim's DNA.

The Biology Project
University of Arizona
Tuesday, August 20, 1996
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