Deck 27: Special Topics 3 Dna Forensics

Question 1

Given the possibility that synthetic DNA could be purposely introduced to a crime scene in order to implicate an innocent person, what methods could be developed to distinguish between synthetic and natural DNA?

Answer 1

DNA profiling or DNA typing is a method developed by Alec Jeffreys to identify different or related individual's based on the characteristics of their DNA. Synthetic DNA is artificial DNA that can be manufactured to match the Short Tandem Repeats (STR) or microsatellite loci of any person's DNA profile. The repeated motifs of STRs are short; that is, between two to nine base pairs which are repeated approximately seven to forty times. These loci are found on nuclear DNA.
Recently, it has been found out by researchers that anyone who has basic knowledge of molecular biology techniques and knows how to use equipments like Polymerase Chain Reaction (PCR), molecular cloning and Whole Genome Amplification (WGA) can produce or manufacture large amounts of artificial ( in vitro synthesized) DNA with any genetic profile that is desired. The artificial DNA can then be introduced at crime scenes or integrated in real human tissues or can even be applied to surface of objects at the crime scene. Current forensic methods and procedures are not able to differentiate between natural ( in vivo generated) and artificial ( in vitro synthesized) DNA.
In synthetic DNA all loci are unmethylated whereas in natural DNA some loci are methylated while some are unmethylated. An authentication assay has been recently developed which is based on analysis of methylation of a set of loci of genome which can differentiate between natural ( in vivo generated) and artificial ( in vitro synthesized) DNA. Using such an assay is necessary to maintain credibility in DNA evidence which is needed in cases of DNA profiling.

Question 2

What is VNTR profiling, and what are the applications of this technique?

Answer 2

DNA profiling is a technique that employs study of DNA to identify an individual in a population. DNA profiling is widely used in genetic studies, forensic analysis. It is an important tool used for criminal investigations. This technique uses VNTR, STR, mitochondrial DNA or SNP to create DNA profiles.
VNTR (Variable number tandem repeats) profiling is the method of determination of DNA pattern of an individual which can be different from others, by analyzing VNTR. This process is mainly based on uniqueness of VNTR sequences in different individuals. VNTRs are nucleotide sequences repeated in non-coding region of chromosome. VNTRs are about 15 to 100 bp in length. Pattern of tandem repeats of VNTR is different in different persons. This helps in DNA profiling.
In VNTR profiling, DNA extracted from a tissue of an individual is fragmented with a restriction endonuclease enzyme. The restriction enzyme cuts on either sides of the VNTR repeats. The fragmented DNA is then size fractionated by gel electrophoresis. The bands formed in the gel are then analyzed by southern blotting technique by using radioactive probes. The radioactively tagged nucleotide fragments are detected by autoradiography. Smaller VNTRs will show greater electrophoretic mobility than that of larger VNTRs. The pattern of bands observed will be unique for each individual.
Applications of VNTR profiling are as follows.
i. VNTR profiling is used in forensic analysis. DNA sample found at the crime scene is collected as evidence and analyzed by this technique. The profile obtained from the evidence DNA is then matched DNA profiles of suspects.
ii. It is used for paternity tests and understanding family relationships.
iii. It is used for identification of casualties in war.
iv. It is also used on evolutionary and genetic inheritance studies.

Question 3

Different countries and jurisdictions have different regulations regarding the collection and storage of DNA samples and profiles. What are the regulations within your region? Do you think that these regulations sufficiently protect individual rights?

Answer 3

DNA profile databases are maintained by many countries which stores DNA profiles of suspects, missing persons and individuals who are convicted of crimes, and also stores DNA profiles of human remains that are yet to be identified. CODIS is a DNA profile database maintained by FBI in U.S. The storing of an individual's genetic information raises ethical and moral issues regarding the violation of the person's civil rights. So, collection of DNA samples and storing of genetic information are guided by strict regulations of government organizations.
The U.S regulations regarding collection and storing of genetic data in DNA profile databases are the following.
i. DNA samples should be collected from convicted felons, individuals who are arrested. Non U.S residents, who are detained, are also required to submit their DNA samples for DNA profiling.
ii. A sex offender or an individual who is convicted of sexual violence of some form should give their DNA for storage in DNA profile databases.
iii. Individuals who are on probation are required to submit their DNA sample to the probation officer.
iv. Individuals who are found to be not guilty due to insanity reasons are also required to give their sample for DNA profiling.
v. The Attorney general can authorize the collection of DNA samples from unwilling convicted felons by restraining.
vi. Individuals who refuse to cooperate in submission of their samples would be penalized.
vii. Authorities are required to analyze the sample and include the data in CODIS.
viii. The DNA Subcommittee is required to oversee the techniques used for DNA profiling.
ix. Post conviction DNA analysis is allowed by the State if the convicted felon can provide enough evidence to support the request of re-analysis of DNA.
The regulations regarding DNA profiling, although intended for law enforcements for the security of the society, raises debate about the breaches of civil and privacy rights in the process. If the securities of DNA databanks are breached, then there will be a serious violation of privacy rights of all the individuals whose data is stored in the databank. Multi layered security arrangement can provide a strong security but it still cannot eliminate hacking of the databank to steal genetic data. DNA data from databases are sometimes used for research purposes, which if exploited, could lead to privacy right violations. Storage of DNA of suspects who were not convicted can raise ethical issues regarding the civil rights of that person. Collection of DNA samples from convicted felons by force would be a violation of civil rights. So, whether these regulations can sufficiently protect a person's privacy rights, is still a debatable issue.

Question 4

Why are short tandem repeats (STRs) the most commonly used loci for forensic DNA profiling?

Question 5

If you were acting as a defense lawyer in a murder case that used DNA profiling as evidence against the defendant, how would you explain to the jury the limitations that might alter their interpretation of the crime scene DNA profile?

Question 6

Describe capillary electrophoresis. How does this technique distinguish between input DNA and amplified DNA?

Question 7

The phenomena of somatic mosaicism and chimerism are more prevalent than most people realize. For example, pregnancy and bone marrow transplantation may lead to a person's genome becoming a mixture of two different genomes. Describe how DNA forensic analysis may be affected by chimerism and what measures could be used to mitigate any confusion during DNA profiling. Find out more about genetic chimerism in an article by Zimmer, C., DNA double take, New York Times , September 16, 2013.

Question 8

What are the advantages and limitations of Y-chromosome STR profiling?

Question 9

How does the AMEL gene locus allow investigators to tell whether a DNA sample comes from a male or a female?

Question 10

Explain why mitochondrial DNA profiling is often the method of choice for identifying victims of massacres and mass disasters.

Question 11

What is a "profile probability," and what information is required in order to calculate it?

Question 12

Describe the database system known as CODIS. What determines whether a person's DNA profile will be entered into the CODIS system?

Question 13

What is DNA barcoding, and what types of cases use this profiling method?

Question 14

Why is it important to understand the prosecutor's fallacy?