Forensics DNA testing

Encoded instructions For all living organisms Are located on long molecules of DNA DNA is a twisted ladder shaped “double helix” Forms tow long complementary chains of nucleotides Four different bases A-adenine T-thymine C-cytosine G-guanine

DNA complementary pairs Adenine always pairs with Thymine Cytosine always pairs with Guanine

Chromosomes: 23 pairs of chromosomes in the nucleus of each cell Each chromosome has a long coiled DNA molecule packaged with protein Full set of chromosomes contain 6 Billion pairs of bases! The bases that code the proteins are called GENES. some of the DNA is non-coding DNA (referred to as Junk DNA)

Traits Eye color Height Weight Personality Susceptibility to numerous conditions Some traits are heavily influenced by the environment and some are not

What is unique about your DNA Unless you have an identical twin, NOBODY has DNA like yours Comparing the DNA sequence for two humans, 999 out of every 1000 pairs will be the same. . . Humans are 99.9% similar! We are also very similar to other species

DNA is like a finger print Semen, blood, saliva and skin can be tested to see if the DNA matches a particular person. Time consuming to test for 6 billion base pairs. DNA fingerprinting in forensics focuses on a few highly variable regions of DNA known as the short tandem repeats (STRs).

Short Tandem Repeats(STR) Is located on the non-coding regions of the DNA 13 core loci that are reviewed on the suspects/victims Once evaluated, it can be compared to a national databank kept by the FBI on criminals and missing persons.

EXONERATIONS: As of 2013, there have been 307 post conviction exonerations in the US based on DNA evidence In 149 of these cases the true source has been identified. Careful police and lab procedures MUST be followed to establish a “chain of custody” for the sample and to prevent cross-contamination.

Other applications of DNA science To identify close relatives To establish paternity To identify genetic risks for mutations Newborn screening for genetic abnormalities that can be treated immediately (ie: PKU)

Techniques for analyzing DNA Karyotyping: technique used for examining the organism’s set of chromosomes. Attention is paid to abnormalities Cell in metaphase is stained and photographed under a microscope Digital images are cut, paired and organized by size so that abnormalities can be detected.

Polymerase Chain Reaction(PCR) PCR is used to make enough copies of the DNA segments so the DNA can be sequenced, profiled and tested for a specific gene trait. PCR allows DNA profiling to be performed on an extremely small sample of DNA

Gel Electrophoresis Technique that separates the molecules by length and charge, including DNA, RNA and proteins. In DNA, the short tandem repeat (STR) are the areas of focus. The fragments are inserted into a special gel and electricity is applied to attract the molecules through the gel. The smaller fragments with fewer STRs move faster. The fragments are stained, banded and compared to other patterns to determine which STR alleles are in the sample.

Microarrays Can detect the presence and activity of thousands of genes at the same time. Made by attaching or printing DNA probes on a glass slide, chip or membrane in and organized array. Probes attach to the complementary DNA Sample DNA is amplified using PCR and cut up using special enzymes that will divide the DNA at specific places.

Micro arrays continued The solution containing the sample DNA is incubated with the microarray When the sample DNA matches the probe DNA, it will stick together and hybridize (and remain on the chip while others wash off). The hybridized probes can be triggered to glow.

Other uses of microarray technology Can give detailed info about ancestry and genes for particular traits Can be used to study which genes are active during development of cancer cells, as well as the response of pathogens to various treatments.

Fingerprints A fingerprint is an impression left by the friction ridges of the human finger. Fingerprints are easily deposited on surfaces by the natural secretions of sweat in our exocrine glands (skin glands). Feet also have friction ridges

Deliberate impressions of fingerprints may be formed by ink or other substances and transferred from the peaks of friction ridges on the skin to a relatively smooth surface such as a fingerprint card. Usually the print is taken from the last joint of the finger or thumb.

Human fingerprints are detailed, unique, difficult to alter and durable over the life of the individual The use of fingerprint technology has led to many crimes being solved.

Explore more Learn. Genetics.utah.edu/content/labs/gel/forensics Review the interactives on: DNA extraction Gel phoresis PCR mortality