MCB 2400 Lecture Notes - Lecture 13: Combined Dna Index System, Amplicon, Capillary Electrophoresis
15 Dec 2016
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DNA in the Cell
• Target specific STR loci (on autosomes) to use for PCR
• Target region for PCR molecular Xeroxing
o tag the copies with a fluorophore
13 Core Loci used in forensics
• Multiplex PCR reaction
• Combining primers for 13 diff types of loci in same reaction mix simultaneously
• Have a way of differentiating different amplicons created
Color detection of fluorescent tags
• Capillary electrophoresis ABI 3130xl autosequencer
• The capillaries carry PCR products through the laser detector
• Separated on basis on length of size and color of amplicon
What is a DNA profile?
• For autosomal genes, each human has 2 copies for every gene, one from our mother and one
from our father
• Together, they make up a genotype for that particular gene, or locus
• Genotypes at many different loci = DNA profile
❖ More loci investigated, higher power of discrimination for profile
• The DNA profile is a unique representation of a specific individual
• Use the product rule to estimate the frequency of the profile in the population and determine
the random match probability
❖ The likelihood someone else just by chance could have this profile
❖ Look at known allele frequencies present in database
❖ Multiple frequencies of all loci/genotypes to get probability of having profile in the
population
Three Possible Outcomes
• Match
o Every position/allele present in suspect profile matches crime scene profile
• Exclusion
o One allele is missing from known suspect profiles, not present in crime scene profile
o Just one allele from one locus
• Inconclusive
o Degraded DNA present at crime scene
o Low copy # like touch DNA
o Not whole DNA
What is the meaning of a match?
• Profiles from convicted offenders, crime scenes, missing persons.
❖ Investigative leads for suspects.
❖ Based on the Product Rule, multiply frequencies of individual alleles in a population to
find the likelihood of a match occurring by chance alone.
❖ Does not tell us whether or not suspect is guilty/innocent
❖ Do not know about time/sequence of events
❖ When DNA came in contact with victim
❖ Provides linkage
• Combined DNA Index System; >12 million offender profiles, 2.4 million arrestee profiles, ~727
thousand forensic profiles as of August 2016.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Dna in the cell: target specific str loci (on autosomes) to use for pcr, target region for pcr molecular xeroxing, (cid:862)tag(cid:863) the copies with a fluorophore. 13 core loci used in forensics: multiplex pcr reaction, combining primers for 13 diff types of loci in same reaction mix simultaneously, have a way of differentiating different amplicons created. Color detection of fluorescent tags: capillary electrophoresis abi 3130xl autosequencer, the capillaries carry pcr products through the laser detector, separated on basis on length of size and color of amplicon. What is a dna profile: for autosomal genes, each human has 2 copies for every gene, one from our mother and one from our father, together, they make up a genotype for that particular gene, or locus. Genotypes at many different loci = dna profile. The likelihood someone else just by chance could have this profile. Look at known allele frequencies present in database.
