In real forensic tests of DNA from a crime scene, technicians would do an analysis conceptually similar to the one in the example above. However, a number of different markers (not just the single marker in the example) would be compared between the crime scene DNA and the suspects' DNA.
Also, the markers used in a typical forensic analysis don't come in just two different forms. Instead, they're highly polymorphic (poly = many, morph = form). That is, they come in many alleles that vary in tiny increments of length.
The most commonly used type of markers in forensics, called short tandem repeats (STRs), consist of many repeating copies of the same short nucleotide sequence (typically, 2 to 5 nucleotides long). One allele of an STR might have 20 repeats, while another might have 18, and another just 10start superscript, 1, end superscript.
By examining multiple markers, each of which comes in many allele forms, forensic scientists can build a unique genetic "fingerprint" from a DNA sample. In a typical STR analysis using 13 markers, the odds of a false positive (two people having the same DNA "fingerprint") are less than 1 in 10 b, i, l, l, i, o, nstart superscript, 1, end superscript!
Although we may think of DNA evidence being used to convict criminals, it has played a crucial role in exonerating falsely accused people (including some who had been jailed for many years). Forensic analysis is also used to establish paternity and to identify human remains from disaster scenes.
In real forensic tests of DNA from a crime scene, technicians would do an analysis conceptually similar to the one in the example above. However, a number of different markers (not just the single marker in the example) would be compared between the crime scene DNA and the suspects' DNA.
Also, the markers used in a typical forensic analysis don't come in just two different forms. Instead, they're highly polymorphic (poly = many, morph = form). That is, they come in many alleles that vary in tiny increments of length.
The most commonly used type of markers in forensics, called short tandem repeats (STRs), consist of many repeating copies of the same short nucleotide sequence (typically, 2 to 5 nucleotides long). One allele of an STR might have 20 repeats, while another might have 18, and another just 10start superscript, 1, end superscript.
By examining multiple markers, each of which comes in many allele forms, forensic scientists can build a unique genetic "fingerprint" from a DNA sample. In a typical STR analysis using 13 markers, the odds of a false positive (two people having the same DNA "fingerprint") are less than 1 in 10 b, i, l, l, i, o, nstart superscript, 1, end superscript!
Although we may think of DNA evidence being used to convict criminals, it has played a crucial role in exonerating falsely accused people (including some who had been jailed for many years). Forensic analysis is also used to establish paternity and to identify human remains from disaster scenes.
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