DNA / Serology
|Contact our DNA / Serology Lab Today!||Dr. Julie Howenstine – Forensic DNA Expert, Biological Evidence Examiner, Crime Scene Investigation, Forensic Veterinary Specialist|
Forensic Serology / DNA Consulting
Speckin Forensic Laboratories are specialists in helping attorneys understand serology and DNA and its relevance to their case. We will provide effective case review and consultation to assure that proper serological and DNA analysis has been conducted.
What is serology?
In a traditional sense serology means the characterization of blood utilizing antigen-antibody tests. The term is used loosely now and encompasses all of the initial location, characterization and isolation of biological fluids for DNA testing. Testing is available for blood (human and animal), seminal fluid, semen (includes sperm cells), amylase (component of saliva), urine, feces, and vomit.
What Is DNA?
DNA (deoxyribonucleic acid) is the genetic material present in the cells of all living organisms. DNA molecules are the fundamental units of heredity. DNA instructs the body cells to make proteins which determine structure and function. DNA is the same in every cell of an individual. Most DNA from person to person is the same. That is what makes us human in structure and function. A small percentage of DNA is different from individual to individual and these differences are the basis for forensic DNA individualization.
How is DNA applied forensically?
Body fluids characterized by serology can be DNA tested and compared to reference samples from victims and suspects. DNA results upon comparison are declared a match, exclusion or the less powerful association of “cannot exclude”. If the DNA from an evidence sample does not match the reference sample, then we can conclude that that individual did not contribute the sample. If a match or a “cannot exclude” result is declared, statistical estimates must then be calculated to determine the significance of the association. DNA can be a very powerful forensic tool for identification or exoneration.
How can the experts at Speckin Forensic Laboratories help?
For both criminal and civil cases, we will assist with motions, hearings and discovery; review completed testing; conduct further testing; facilitate retesting; prepare attorneys for cross-examination of witnesses; and provide effective expert testimony. We can also utilize serology and DNA testing methods to answer specific questions of sexual fidelity.
The first step in a matter with DNA evidence is to obtain and analyze the under lying DNA data from the electropherogram (EPG’s). This will show, among other things, possible contamination, additional donors, and concerns or errors with collection, handling, and analysis.
Below is an example of a case that was processed by the State Police. The first issue was the analyst contaminated THREE different samples with the analyst’s DNA in the analysis & processing phase.
In this case, even with the contamination issue it was still apparent that an additional donor was present. Without review of the under lying data this would never have come to light. The Police Lab report made no mention of this terrible blunder, nor the additional person present.
What kinds of bodily fluid/materials can be analyzed for serology and/or DNA?
Seminal fluid and/or semen
Aborted embryo/fetal tissue
What types of cases would you need a Forensic DNA expert?
In criminal cases such as murder, rape, firearms possession and burglary. In civil cases such as anonymous letters and identification.
How long do biological samples persist?
This varies depending on the biological material, initial collection, activity since deposition, and storage of the evidence. Samples still viable for DNA testing have been known to persist for multiple decade.
What is DNA Profiling?
Forensic DNA profiling (also called DNA testing or DNA typing) is a technique employed by forensic scientists to identify individuals by characteristics of their DNA. DNA profiles are a small set of DNA variations that are very likely to be different in all unrelated individuals. DNA profiling should not be confused with full genome sequencing. DNA profiling is used in, for example, parentage testing and criminal investigation.
Although 99.9% of human DNA sequences are the same in every person, enough of the DNA is different that it is possible to distinguish one individual from another, unless they are monozygotic (“identical”) twins. DNA profiling uses repetitive (“repeat”) sequences that are highly variable, called variable number tandem repeats (VNTRs), in particular short tandem repeats (STRs). VNTR loci are very similar between closely related humans, but are so variable that unrelated individuals are extremely unlikely to have the same VNTRs.
The DNA profiling technique was first reported in 1985.
Short Tandem Repeats (STRs)
The human genome is full of repeated DNA sequences. These repeated sequences come in various sizes and are classified according to the length of the core repeat units, the number of contiguous repeat units, and/or the overall length of the repeat region. DNA regions with short repeat units (usually 2-6 bp in length) are called Short Tandem Repeats (STR). STRs are found surrounding the chromosomal centromere (the structural center of the chromosomes). STRs have proven to have several benefits that make them especially suitable for human identification.
STRs have become popular DNA markers because they are easily amplified by polymerase chain reaction (PCR) without the problem of differential amplification; that is, the PCR products for STRs are generally similar in amount, making analysis easier. An individual inherits one copy of an STR from each parent, which may or may not have similar repeat sizes. The number of repeats in STR markers can be highly variable among individuals, which make these STRs effective for human identification purposes.
For human identification purposes, it is important to have DNA markers that exhibit the highest possible variation in order to discriminate between samples. It is often challenging to obtain PCR amplification products from forensic samples because either the DNA in those samples is degraded, or mixed, such as in a sexual assault case.
The smaller size of STR alleles make STR markers better candidates for use in forensic applications, in which degraded DNA is common. PCR amplification of degraded DNA samples can be better accomplished with smaller target product sizes.
Because of their smaller size, STR alleles can also be separated from other chromosomal locations more easilyto ensure closely linked loci are not chosen. Closely linked loci do not follow the predictable pattern of random distribution in the population, making statistical analysis difficult.
STR alleles also have lower mutation rates, which makes the data more stable and predictable.
Because of these characteristics, STRs with higher power of discrimination are chosen for human identification in forensic cases on a regular basis. It is used to identify victim, perpetrator, missing persons, and others.
Beginning in 1996, the FBI Laboratory launched a nationwide forensic science effort to establish core STR loci for inclusion within the national database known as CODIS (Combined DNA Index System). The 13 CODIS loci are CSF1PO, FGA, TH01, TPOX, VWA, D3S1358, D5S818, D7S820, D8S1179, D13S317, D16S539, D18S51 and D21S11. These loci are nationally and internationally recognized as the standard for human identification.
|Contact our DNA / Serology Department Today!||Dr. Julie Howenstine – Forensic DNA Expert, Biological Evidence Examiner, Crime Scene Investigation, Forensic Veterinary Specialist|