Chapter 5:DNA FingerprintingMS. COLABELLI

O.J. SimpsonA Mountain of Evidence

On June 12, 1994, police arrived at the home of Nicole Simpson only to view a horrific scene. The bodies of O.J. Simpson’s estranged wife and her friend Ron Goldman were found on the path leading to the front door of Nicole’s home. Both bodies were covered in blood and had suffered deep knife wounds. Nicole’s head was nearly severed from her body. This was not a well-planned murder. A trail of blood led away from the murder scene. Blood was found in O.J. Simpson’s Bronco. Blood drops were on O.J.’s driveway and in the foyer of his home. A blood-soaked sock was located in O.J. Simpson’s bedroom, and a bloodstained glove rested outside his residence.

O.J. SimpsonA Mountain of Evidence

As DNA was extracted and profiled from each bloodstained article, a picture emerged that seemed to irrefutably link Simpson to the murders. A trail of DNA leaving the crime scene was consistent with O.J’s profile, as was the DNA found entering Simpson’s home. Simpson’s DNA profile was found in the Bronco along with that of both victims. The glove contained the DNA profiles of Nicole and Ron, and the sock had Nicole’s DNA profile. At trial, the defense team valiantly fought back. Miscues in evidence collection were craftily exploited. The defense strategy was to paint a picture of, not only an incompetent investigation, but one that tinged with dishonest police planting evidence. The strategy worked. O.J Simpson was acquitted of murder.

https://www.youtube.com/watch?v=-qxrDkMieQs

Introduction No two people on Earth have the same DNA

◦ Except for identical twins

DNA technology has allowed criminal cases to be solved that were once not possible to conclude

Since 1980s, DNA evidence has been used to ◦ Investigate crimes◦ Establish paternity ◦ Link a suspect to a crime◦ Eliminate a suspect◦ Identify victims of war/large-scale disaster

DNA evidence is individual evidence because it can track back to one person◦ Can also be trace evidence when a small amount is left behind

The Function & Structure of DNA

DNA contains the genetic material that holds the information to produce proteins and replicate itself

DNA is stored in animal cells into a structure called a chromosome

DNA is made up of two strands tightly coiled called a double helix

The backbone of DNA is alternating sugar (deoxyribose) and phosphate

Made up of four bases◦ Adenine to thymine◦ Guanine to cytosine

Every organism has a specific number of chromosomes◦ Humans have 23 pairs◦ Dogs have 39 pairs

The Function & Structure of DNA

Nuclear DNA◦ Double helix shape◦ Inherited from BOTH parents◦ Half of genetic information from each parent

◦ DNA from egg cell from mom◦ DNA from sperm cell from dad

mtDNA◦ Found only in mitochondria organelles◦ Animal cells contain multiple mitochondria◦ Loop shaped chromosome◦ Inherited ONLY from mother◦ Passed to offspring in cytoplasm from egg cell

Genes & Alleles Genes

◦ DNA sequences with instructions for traits ◦ Ex: blood type

Allele◦ Alternative forms of a gene◦ Ex: if the gene is eye color, the alleles

would be brown and blue

Genome◦ Complete set of DNA in a cell ◦ Chromosomal and mitochondrial

Genes & Alleles Exons

◦ DNA encoded to make proteins and other molecules◦ Exit the nucleus to make proteins (expressed)◦ Less than 1.5% of your genome

Introns◦ Non-coding regions of DNA◦ Stay in the nucleus and are never coded◦ Some functions for gene splicing and gene regulation◦ Remainder of introns has an unknown function

DNA Identification Most of human genome is the same

The areas of variation are in the introns or the non-coding regions of DNA◦ Repeated base sequences◦ Individuals have unique patterns or repeat sequences

◦ Different lengths and sequences of the bases◦ Called polymorphisms

DNA Fingerprinting or DNA Profiling◦ Takes the pattern of bands on X-Ray film◦ Polymorphisms produce unique band patterns ◦ Forensic scientists focus on STR sections

STR – Short Tandem Repeats

Short sequence of DNA - between 2-5 bases in length

Found in great abundance in the human genome

Becoming a preferred method of analysis◦ More accurate◦ Small & partially degraded DNA

samples can be analyzed

Hundreds of different types in human genome

DNA Fingerprinting◦ DNA can be extracted from small samples of biological evidence

◦ Saliva – envelope, toothbrush, bite wound

◦ Hair follicle

◦ Blood

◦ Seminal fluid

◦ Skin cells

◦ DNA fingerprint developed when several different STRs are examined

◦ Tissue matching◦ When two samples have the same band pattern from the same person

◦ Crime-scene evidence matches

DNA Fingerprinting Preparing DNA Samples

◦ When DNA is mixed with special enzymes that cut DNA in specific places, it will form different sized DNA fragments

◦ Using a technology called Gel Electrophoresis, these DNA fragments can be separated within a gel

◦ The results will form band patterns (or fingerprint) in the gel specific to that individual

◦ Relatives may share some bands and this is how this technology can be used to identify inheritance and paternity

https://www.youtube.com/watch?v=ZxWXCT9wVoI

DNA Fingerprinting Steps

1. Extraction◦ Cells isolated from tissue◦ DNA is extracted from the nucleus of the cells collected

2. Restriction Enzymes◦ DNA is cut into fragments using biological scissors known as restriction

enzymes◦ These molecules recognize specific sequences in the DNA sample and cut

in those specific locations◦ Ex: Hind III recognizes the AACGTT base sequence and cuts between the two AA bases

◦ These sequences of tandem repeats are known as VNTR sequences (Variable Number Tandem Repeats)

◦ Shorter sequences about 2-5 bases in length are known as STR sequences (Short Tandem Repeats)

DNA Fingerprinting Steps

3. Amplification◦ Small samples of DNA evidence can be amplified or copied in a

process called the Polymerase Chain Reaction (PCR)◦ Multiplexing – simultaneously extracting DNA and amplifying

4. Electrophoresis◦ DNA is loaded into wells of an agarose gel◦ Separate molecules within an electric field◦ Negatively charged DNA fragments move to positive end of the gel◦ The process will separate the fragments of DNA by their size

◦ Smaller fragments of DNA will travel faster and farther down the gel

DNA & Probes If there are too many DNA restriction fragments, scientists use probes to identify specific DNA sequences

Helps to make any DNA on the gel visible

Made of synthetic DNA that is complementary to a fragment

For example, a probe AAGCTTA will find a TTCGAAT fragment and attach

If probe is fluorescent, then you use a UV light to see the probes

If probe is radioactive, then you use X-Ray film to see the probes◦ Called autoradiograph

Population Genetics & DNA Databases

Study of variation in genes among a group of individuals

Proportion of people in a population with a particular characteristic is determined by the proportion of the alleles for these traits in a population

Example:◦ Asian population - blue eyes rare, few people have allele that codes

for blue eyes◦ Northern Europeans - blue eyes common, more people have allele

that codes for blue eyes◦ Europe/Great Britain/US - 46% have type O Blood◦ South America - almost 100% type O blood

Collection & Preservation of DNA Evidence

Extremely small samples can become contaminated

◦ Sneezing◦ Coughs◦ Evidence collector touches own mouth

or nose

To avoid contamination◦ Wear disposable gloves and change often◦ Use disposable instruments for handling each

sample◦ Avoid touching area where DNA may exist◦ Avoid talking, sneezing, coughing over evidence◦ Avoid touching face, nose, mouth when collecting

and packaging◦ Air-dry evidence thoroughly before packaging◦ Place evidence in new paper bags/envelopes◦ If wet evidence can not be dried, may be frozen

to preserve◦ Keep evidence cool and dry during transportation

and storage◦ Mold can damage DNA

◦ Avoid plastic bags for DNA evidence◦ Direct sunlight and warm conditions can harm

DNA

Analysis of DNA Fingerprints

Which man is the father?◦ Can either man be excluded as the father?◦ Which man may be the father of the child?◦ Is this DNA profile sufficient to establish paternity?

Paternity Child inherits one gene from each parent

If two genes from parents are different, then two bands appear in child’s DNA fingerprint

If two genes are identical, only one band appears

The more probes used in DNA fingerprint, the greater the accuracy of the DNA fingerprint

Most criminal cases use 6-8 probes

Analyze both position and width of the bands

All bands have to match exactly

Analysis of DNA Fingerprints

Some countries have databases of DNA profiles

US has CODIS◦ Combined DNA Index System◦ Electronic database of DNA profiles◦ Every state maintains a DNA index of individuals convicted of rape,

murder, child abuse

Probability of identity is a measure of the likelihood that two individuals selected at random will have an identical STR type

STR’s occur independently, probability of having a particular combination of STR types is determined by the product of their frequency in a population

The Break-in… One afternoon, a break-in occurred at a high school, and several computers were stolen. At the time of the break-in, the building was empty. A motion detector tripped by movement in one of the hallways alerted the police. When the police arrived to investigate, they found that one of the doors leading into the school had been propped open with paper wedged into the door-jamb. The door appeared to be locked, but it could easily be pushed open. Near the door, police found a cold soft drink can. Because of the cool temperature of the drink, police suspected that the can was left by one of the intruders.

The can was bagged as evidence, and in the forensics lab, a DNA sample was obtained from the lip of the can. The neighborhood was canvassed, and a clerk in a convenience store remembered selling canned soft drinks to two young males just before the break-in occurred. The surveillance video in the convenience store was examined, and the clerk provided the police with the names of all males who were in the store just prior to the break-in. Three suspects were identified from the surveillance video.

Using a DNA sample found from the soft drink can collected at the crime scene, a PCR was run to amplify the amount of DNA, and then a DNA profile was performed. Cheek swabs were obtained from the 3 suspects, and their DNA was tested.

Match the crime scene DNA with a DNA sample from the 3 suspects.

The Break-in DNA Fingerprint Results

1. Does the crime scene DNA match the DNA from any of the suspects?

2. Is there more than one DNA match?

3. Is this DNA profile sufficient to convict a suspect?

Who Are the Parents? Who are the Parents?

Three baby boys were born on the same morning in the same hospital. That morning, the hospital had started using new identification bracelets. When the babies were bathed, the ID bracelets slipped off and the nurses thought a mix-up might have occurred.

Recall that 50 % of a child's DNA is obtained from each parent.

Use a ruler to align the DNA bands of the baby with any DNA bands of the parents. Determine if any parents share the same band of DNA with the babies.

There is only one correct set of parents matching a baby.

1. Which baby belongs to the Meanys?

2. Which baby belongs to the Glicks?

3. Which baby belongs to the Moes?

4. Is it possible for a child to have a DNA band that is not found in the mother's DNA?

Do Now A young woman claimed that her son was born as the result of an affair with a famous athlete who was a multimillionaire. The athlete denied paternity, so the woman took her case to court, and sued for an extremely generous child support payment. The three individuals gave blood samples for DNA analysis, and the fingerprints are shown below.

Was the woman's claim justified?

Do Now Do Now:

The fingerprints to the right are from a Guatemalan family. A woman claimed that

her daughter was born in Canada and emigrated to Guatemala to join her father. When she wanted to

return to Canada, the immigration authorities claimed that she was not the woman's real daughter.

On the basis of the evidence is the woman's claim true?

Jimmy Solo, a famous rock star, returned to his New York mansion from an appearance in Toronto. As Jimmy entered the side entrance he noticed a great mess in the living room and den. Drawers had been emptied; couch cushions ripped open; the furniture was in disarray and the wall safe in the study was open. He stormed upstairs to see if his expensive jewelry collection had been touched and upon doing so heard someone in his bedroom. He grabbed a small metal statue and rushed into his bedroom surprising the thief. In the ensuing struggle the thief's gun discharged killing Jimmy instantly.

The next day the housekeeper found Jimmy dead on the floor and immediately contacted the police. The subsequent investigation identified seven possible suspects.

1. Willie James - lead guitarist in Jimmy's band who was constantly upstaged and underpaid by Jimmy2. Samantha Smith - Jimmy's former girlfriend who was dropped by him following three years of

cohabitation3. Lucifer - Jimmy's bodyguard who is extremely jealous of Jimmy's wealth4. Jamie Waite - Jimmy's manager who has accumulated massive gambling debts5. Dicky Schultz - a former acquaintance of Jimmy's who claims he is owed thousands for past services6. Casparina - Jimmy's new girlfriend who is under pressure from former friends to pay back large

loans7. Jimmy The Weasel - a former friend of Jimmy who was promised a position in Jimmy's band that

never materialized

It was established that all had a motive for killing Jimmy and none had an ironclad alibi. The police realized they had a problem and consequently decided to undertake a DNA fingerprinting of all suspects and from a blood sample taken from the crime scene.