Services

Forensic Casework Analysis
Paternity Testing
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Specialized Services


Technologies Offered

STR DNA Analysis
Y-STR DNA Analysis
mini-STR DNA Analysis (also known as MiniFiler™)

STR DNA Analysis

Short tandem repeat (STR) technology is a forensic analysis that evaluates specific regions (loci) that are found on nuclear DNA. The variable (polymorphic) nature of the STR regions that are analyzed for forensic testing intensifies the discrimination between one DNA profile and another. For example, the likelihood that any two individuals (except identical twins) will have the same 13- loci DNA profile can be as high as 1 in 1 billion or greater. The Federal Bureau of Investigation (FBI) has chosen 13 specific STR loci to serve as the standard for CODIS. The purpose of establishing a core set of STR loci is to ensure that all forensic laboratories can establish uniform DNA databases and, more importantly, share valuable forensic information. If the forensic or convicted offender CODIS index is to be used in the investigative stages of unsolved cases, DNA profiles must be generated by using STR technology and the specific 13 core STR loci selected by the FBI.

Y-STR DNA Analysis

Y- STRs are Short Tandem Repeats found on the male-specific Y Chromosome. The coding genes, mostly found on the short arm of the Y Chromosome, are vital to male sex determination, spermatogenesis and other male related functions. The Y-STRs are polymorphic among unrelated males and are inherited through the paternal line with little change through generations.

Y-STRs are commonly used to examine sexual assault evidence. In a sexual assault case, evidence such as vaginal swabs will contain both female and male DNA. Differential extraction is often used to separate the male component from the female component. More often, however, the male and female components cannot be separated completely. As a result, the female component could exist prominently even in the male component after separation. When the “male DNA sample” undergoes the PCR amplification process, the female DNA component is amplified as well, sometimes masking the male DNA, which makes analysis difficult.

Masking does not occur when Y-STRs are examined. Since there is no Y-STR in the female evidence, the only contribution of Y-STR can only come from the assailant(s) in a sexual assault case. The male component will be easily detected, since only this part of DNA will be amplified. The Y-STR system is especially helpful when there are more than one assailant. The mixed pattern in the evidence can help to identify those males responsible for the assault.

Y-STR is also used for non-sexual assault cases where mixed samples are collected from evidence. Sometimes, regular STR will cause the masking effect if there is a very small quantity of male DNA in the mixed sample. Performing Y-STR testing can help to identify all males who have contributed to the evidence.

mini-STR DNA Analysis

mini-STRs were first used extensively in a forensic lab to help identify the victims of the World Trade Center disaster. They were needed because many of the remains collected from the debris left where the Twin Towers once stood were extremely degraded from fire, heat, and sometimes bacterial degradation.

mini-STR testing is used in cases where very small or extremely degraded samples are the only evidence available. Degraded samples typically can include bones, teeth, burnt items, items exposed to heat and humidity, etc. Degraded samples consist of DNA that is highly fragmented or broken down. mini-STRs are a miniaturized version of the traditional STRs (Short Tandem Repeats) that are used by every forensic lab in the country. They incorporate the same loci, or locations, on the DNA molecule that are typed using available commercial kits such as Applied Biosystem's Identifiler kit, and thus contain the same locus that are in the National DNA database called CODIS (Combined DNA Index System) but there is a very big difference.

mini-STRs create DNA fragments that are many base pairs less in length than traditional STR markers. This is accomplished through moving the location of the primers (which serve as markers to indicate where copying should begin during the PCR (polymerase chain reaction) closer to the repeating DNA segment of interest. What all this means is that DNA results that were once simply not possible to obtain—now can be. (Source: Suzanna Ryan - www.lawofficer.com)

Cold cases can also benefit from mini-STR testing. Samples that even a year or two ago would not be considered good candidates for DNA testing may now yield results with the extremely sensitive MiniFiler™ kit.