Ch 7 (DNA Profiling) Test

DNA Profiling

Technique used to identify person based on their genetic code

• Pattern of DNA fragments obtained by analyzing noncoding DNA sequences

• No-one shares DNA, except identical twins

• Forensic DNA analysis identifies suspects, victims and closely related relatives

Polymorphisms

Regions of DNA where high variation occurs among individuals

• Occur in less than 1% of DNA

DNA Identification Act

Gov’t legislation that provided funds to improve forensic labs and communication among law enforcement

CODIS

Combined DNA Index System that collects, analyzes and communicates criminal DNA info and profiles of missing persons/ unidentified remains among law enforcement

DNA

Genetic material of all living things

• Mostly noncoding

  • Regulate RNA & protein production

• Sugar, nitrogen base and phosphate group

Nucleotide bases

Building blocks of DNA/RNA, carrying genetic info

• Genetic code of DNA written in order of these

• A,T,C and G

Chromosome

DNA twisted around histones, so DNA fits into the nucleus

• 46, 2 of which determine sex

• Each parent contributes one member of each pair

Human genome

All DNA found in human cells

• Human Genome Project sequenced

• ~21,000 protein coding genes w/ 3,000 base pairs each

• 99.9% same among humans

Genes

Basic, functional unit of heredity

Alleles

Gene differences/ variable forms of gene

Gel electropheresis

DNA cut into fragments, separated by size on a gel as they migrate towards the positive end of the gel, radioactive probes ID repeating untis of DNA appearing as a series of distinctive bands

STR profiling

Graphic analysis of someone’s STR alleles used for unique identification

• Short tandem repeats

• Analyzing variable regions of DNA STRs consist of fewer than 50 bases

  • More easily recovered from degraded/ limited DNA

• For each STR, inherit one from mom and one from dad

• Contains alleles for all 20 markers + AMEL

• NIST completed pop. Studies to determine allele frequencies of each STR marker to determine probability that random person would have same DNA profile

• Machines/ computerized data interpretation determine it

Markers

Specific locations on chromosomes where STR sequences found

AMEL

Non-STR marker used to determine if DNA is male or female

Allele Frequency

Calculation of how often a particular allele appears w/in given population

SNP profiling

Uses single base substitutions  to distinguish one person’s DNA from another

• Single Nucleotide Polymorphism

  • Variation at just one location

• Multiple markers analyzed to distinguish b/w people

DNA phenotyping

Uses DNA to describe what a person looks like

Snapshot

DNA phenotyping tool that produces a composite sketch of person from their SNP profile

Next generation sequencing

technology for rapidly sequencing DNA or RNA by analyzing millions of small DNA fragments simultaneously

DNA mining

analyze individual SNPs and billions of SNP combinations from thousands of people to identify genetic markers associated with different phenotypes

MtDNA

Maternal lineage over generations can be determined by examination of two regions

Y-chromosome analysis

Identification of STRs found on Y chromosome used to identify male DNA

PCR

Polymerase chain reaction; copies DNA evidence so that a DNA profile can be generated from limited resources

Serologist

Specialist in analysis of bodily fluids

• Determines if evidence source human and sends human samples for DNA analysis

Limitations of DNA

• Limited funds w/ taxpayers paying for new databases

• Public databases= concern about invasion of privacy

• High possibility of contamination

Limiting factors of DNA analysis and their improvemenr

• Cost (suspects claiming innocence may not be able to afford testing)→ DNA Identification Act

• Up to 6-8 weeks w/ backlog → Rapid DNA kits creating profile w/in 90 minutes

• Unable to analyze degraded DNA → STR analysis

• Difficult to share info among law enforcement → DNA Identification Act and CODIS

Collection of DNA

• Photograph, document, properly package

• Need to know where to look, as most DNA evidence not visible

• Avoid contamination w/ gloves, disposable instruments, avoiding touching areas DNA may exist, etc.

• Keep cool, dry and out of direct sunlight

  • Moisture can compromise DNA evidence

  • Humidity → mold

• Validity depends on proper collection, documentation, storage and processing