Random match probability (RMP) is a statistic in
population genetics
Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and pop ...
used to measure the probability of an unrelated person,
random
In common usage, randomness is the apparent or actual lack of pattern or predictability in events. A random sequence of events, symbols or steps often has no order and does not follow an intelligible pattern or combination. Individual rando ...
ly picked out of the population having a genotype that matches the genotype of another individual. In forensic DNA analysis the genotype used to determine RMP is derived from an evidence sample.
To calculate a random match probability, first use a population database to find
allele
An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution.
::"The chro ...
frequencies
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from '' angular frequency''. Frequency is measured in hertz (Hz) which is e ...
for the different alleles present at a
locus
Locus (plural loci) is Latin for "place". It may refer to:
Entertainment
* Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front
* ''Locus'' (magazine), science fiction and fantasy magazine
** ''Locus Award ...
. Databases that account for different subgroups within a population are necessary for RMP because some alleles are more common within certain ethnic/racial group than in others. This means that the random match probability for someone of Caucasian descent could be different than the random match probability for someone of African American descent, even with the same genotype. Using the appropriate database, multiply the frequencies of the alleles present at the target loci to get the RMP at that locus. When the genotype is homozygous at that locus then use the squared value of the frequency for its RMP (
). When the genotype is heterozygous at a locus multiply the different frequencies together, then by two for the RMP (
). Multiply the RMP of each locus together to get the overall RMP for the genetic profile derived from the evidence.
In
forensic science, evidence from the crime scene is gathered and when DNA is present a genetic profile may be found. The genotypes in the profile or profiles found can then be matched with a suspect or used to exclude a suspect. The RMP is useful for the jury because it gives a numeric value to measure how small the chance is that a random individual contributed to the DNA in the evidence and not the suspect.
RMP is used as a tool to measure the rarity of a genetic profile and not as a statement toward the innocence or guilt of a suspect.
See also
*
Random man not excluded
References
Population genetics
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