Exam #4 BIOTECH Flashcards
What is forensic science?
The intersection of law and science used to investigate crimes and analyze evidence.
What are some historic examples of forensic science methods?
1800s: Photography for documenting crime scenes.
Early 1900s: Fingerprinting for identifying individuals.
What is molecular evidence in forensic science?
Analyzing DNA, which carries a unique set of alleles specific to each individual.
How does DNA differ from person to person?
While the chemical structure of DNA is the same, the order of base pairs differs.
Every cell contains a complete set of..
DNA that identifies the organism as a whole.
How much of an individual’s DNA is unique compared to others?
Only one-tenth of 1% (0.1%) of DNA; equating to about 3.2 million nucleotide differences.
When was DNA Fingerprinting/DNA Profiling introduced?
1985
Who invented DNA fingerprinting
Sir Alec Jeffreys
What technique did Sir Alec Jeffreys invent for DNA analysis?
Restriction Fragment Length Polymorphism (RFLP) technique.
What are Variable Number of Tandem Repeats (VNTRs)?
Repetitive patterns of DNA present in all mammalian genomes; discovered by Alec while using RFLP.
What is the unique signature found in each person’s genome?
A pattern of VNTRs and other DNA sequences that differ from individual to individual, forming their DNA fingerprint.
How does RFLP work in DNA fingerprinting?
RFLP involves digesting DNA into fragments of different lengths using restriction enzymes, then analyzing the patterns of fragments to create a “fingerprint.”
What type of genetic markers are most RFLP markers?
di-allelic and co-dominant, meaning both alleles in a heterozygote can be detected.
Are RFLP markers specific to certain loci?
Yes, RFLP markers are highly locus-specific, meaning they target specific locations in the genome.
RFLP inheritance
from mother and father.
How is DNA used in rape investigations?
DNA from evidence, such as vaginal swabs, is compared to known samples from the victim and defendant to identify a match using techniques like RFLP or PCR.
What does an autoradiograph show in DNA profiling?
It displays the patterns of DNA fragments from various samples, such as blood or swabs
What samples are typically analyzed in a rape investigation using DNA profiling?
- Known blood sample of the victim.
- Known blood sample of the defendant.
- DNA size markers for reference.
- Female fraction from the victim’s vaginal swab.
- Male fraction from the victim’s vaginal swab.
What are the two main types of forensic DNA testing?
RFLP (Restriction Fragment Length Polymorphism) and
PCR (Polymerase Chain Reaction) w VNTR
What are the key features of RFLP in forensic DNA testing?
- Requires larger amounts of DNA.
- DNA cannot be degraded.
- No prior sequence information is needed.
What are the key features of PCR in forensic DNA testing?
- Requires much less DNA.
- DNA can be partially degraded.
- Extremely sensitive to contaminating DNA.
- Requires prior sequence information.
Why are DNA size markers important in DNA profiling?
They provide a reference to determine the sizes of DNA fragments in forensic samples.
VNTRs are highly —, with a very large number of —.
polymorphic; alleles
What are Microsatellites or Short Tandem Repeats (STRs)?
Repetitive DNA sequences:
2-6 base pairs long, repeated 5-50 times, and inherited from both mother and father.
What percentage of mammalian genomes is composed of STRs
3-5%
What is slippage during replication?
Slippage during replication is when DNA polymerase misaligns on the template strand, leading to errors in STR sequences.
How does slippage cause STR expansion?
When the newly synthesized strand loops out, leading to the addition of extra repeat units and STR expansion.
How does slippage cause STR contraction?
When the template strand loops out, resulting in the loss of repeat units and STR contraction.
How many STRs has the FBI chosen for DNA fingerprinting?
The FBI initially chose 13 unique STRs
What is CODIS?
CODIS stands for the Combined DNA Index System, the FBI’s database for storing and comparing DNA fingerprints.
When did CODIS become fully operational?
1998
What are the odds that 2 individuals will have the same 13 loci DNA profile
The odds are more than one in a billion, making the profile virtually unique
When did the FBI increase the number of required loci for DNA fingerprinting?
As of January 2007, the FBI required 20 loci for DNA fingerprinting.
Why did the FBI increase the number of loci analyzed in DNA fingerprinting?
Increasing the number of loci enhances the accuracy and discriminatory power of DNA profiling.
What is the role of PCR primers in STR analysis?
PCR primers anneal to unique sequences flanking the variable STR repeat region, allowing amplification of the repeat region for analysis.
What does “12 GATA repeats” represent in STR analysis?
It indicates that the individual has 12 repeats of the GATA sequence at a specific STR locus. Only the number of repeats is reported.
How are STR repeat numbers like “12 GATA repeats” determined?
The repeat number is determined by analyzing the length of the amplified DNA fragments using capillary electrophoresis or gel electrophoresis.
What are two methods to purify DNA for fingerprinting?
- Chemically: Using detergents to break down cell membranes.
- Mechanically: Applying pressure to force DNA out of cells.
What precautions should be taken during DNA collection to avoid contamination?
- Wear disposable gloves and change them frequently.
- Use disposable sample-collecting instruments.
- Avoid talking, sneezing, coughing, or touching your face, nose, or mouth.
- Air-dry evidence before packaging to prevent mold growth.
What are the main enemies of DNA evidence?
- Sunlight and high temperatures: Can degrade DNA.
- Bacteria: Can contaminate or break down DNA.
- Moisture: Encourages mold growth, which can damage samples.
What is the best sample from a suspect’s DNA
fresh, whole blood; Leukocytes (white blood cells).
How old can a DNA sample be and still be analyzed successfully?
DNA can be retrieved and analyzed from samples that are over a decade old using PCR.
What role does PCR play in analyzing degraded DNA samples?
Amplifies DNA found at crime scenes into an amount that can be analyzed.
How are specific STR sites amplified during PCR?
DNA primers are designed for the flanking regions of CODIS sites, enabling targeted amplification of specific STR regions.
What special feature must one of the PCR primers have in DNA fingerprinting?
One of the 2 primers must be fluorescently labeled.
What information can be determined from STR analysis?
The number of repeats in each allele on homologous chromosomes at specific STR loci.
What is the basis of DNA testing in forensic science?
DNA testing is based on exclusion, continuing only until a difference is found.
What happens if no differences are found during DNA testing?
If no differences are found after statistically sufficient testing, the probability of a match is considered high.
Is eyewitness testimony more reliable than DNA testing in forensic cases?
No, DNA testing is considered more reliable as eyewitness accounts can be influenced by biases and errors.
What happened in the Forest Hills Rapist case in Queens, NY (1987)?
Victor Lopez was tried for the sexual assault of three women, despite eyewitnesses describing the assailant as a black man. Lopez, who was not black, was linked to the crimes through DNA evidence.
How was DNA used after the World Trade Center attack on September 11, 2001?
DNA techniques were used to identify the remains of victims amidst tremendous debris, heat, and microbial decomposition.
What challenges did forensic scientists face when using DNA to identify victims of the World Trade Center attack?
Challenges included processing hundreds of thousands of tissue samples from nearly 30,000 individuals, dealing with heat damage, microbial decomposition, and massive debris.
What types of samples were used for DNA isolation after the World Trade Center attack?
cheek swabs from relatives and personal items from the missing.
What DNA analysis techniques were used to identify victims of the World Trade Center attack?
Short Tandem Repeat (STR) analysis, mitochondrial DNA (mtDNA) analysis, and Single Nucleotide Polymorphism (SNP) analysis.
What major natural disaster occurred in December 2004, and what was the death toll?
The South Asian Tsunami occurred in December 2004, resulting in the loss of over 225,000 lives.
How many tsunami victims were identified within three months of the disaster?
800.
What DNA techniques were used to identify victims of the South Asian Tsunami?
mtDNA and Y-STR’s
Why were mtDNA and Y-STR analysis used in identifying tsunami victims?
These methods are effective in analyzing degraded samples; mtDNA is maternally inherited, and Y-STR analysis can trace paternal lineages.
How many DNA samples were collected in the Simpson/Goldman murder case
45 samples
What was announced in the pre trial hearings (1995)
DNA collected matched O.J’s
Why was DNA evidence not effective in the Simpson/Goldman murder case?
The DNA evidence was challenged due to concerns about potential contamination and mishandling of the evidence during collection and testing.
Why is the chain of custody important in DNA analysis?
The chain of custody ensures that evidence is systematically recorded and access is controlled, preventing compromise or contamination of samples.
What challenges arise when presenting DNA evidence to juries?
DNA evidence must be clearly explained, as statistics like “1 chance in 50 billion” can confuse juries and lead to disproportionate focus on the improbable outcome.
