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STR Analysis - Short Tandem Repeat

By: Ian Murnaghan BSc (hons), MSc - Updated: 9 Apr 2018 | comments*Discuss
 
Dna Short Tandem Repeat Analysis

STR analysis refers to 'short tandem repeat.' This type of DNA analysis works to examine individual areas in DNA. The differences for certain DNA regions in one person versus another can allow for distinguishing between individuals. Despite the fact that humans share the overwhelming majority of the same DNA, the tiny fraction of a percent that varies can be exploited to create a profile of the individual.

In criminal investigations, there are thirteen regions that are analysed and compared to establish profiles. In fact, DNA databases used at the government level involve the sequence of these thirteen regions. The chances of two people having the exact same thirteen regions is virtually impossible - likely one in a billion. A common DNA joke is that a person's odds of winning the lottery are higher than finding a perfect match for the thirteen regions. Through STR analysis, an accurate genetic fingerprint of a person can be created and used for a number of important applications.

Performing STR Analysis

STR analysis involves the extraction of nuclear DNA from cells in a sample. Certain regions of the DNA that are extracted are then amplified by the polymerase chain reaction. After amplification, a scientist performs gel electrophoresis to find out how many repeats of the STR sequence exist. Different dyes are used, which might be fluorescent dyes or alternately, silver staining could be used to provide the necessary visual assessment of the DNA.

Using STR Analysis

In forensic laboratories, there are thirteen STR loci that are typically used to create a genetic fingerprint of an individual. Although controversial, the profile is kept in DNA databases. In the United Kingdom (UK), this is the UK National DNA Database and in the United States, the genetic fingerprints are kept in various Combined DNA Index Systems (CODIS) databases ranging from the smaller, local levels to the national level.

Benefits of STR Analysis

STR analysis is still somewhat of a new technology in forensic science. In fact, it was only towards the end of the 1980s that the technique started to become more widely used. Currently, it is a popular method for genetic profiling and STR analysis used today involves four to five nucleotide repeats, which allows scientists to obtain relatively precise and accurate information. In addition, this type of approach allows for somewhat 'mistake-proof' information to be gathered even in poor conditions. If a repeat sequence is shorter, there are problems that occur. A number of genetic conditions are linked to three nucleotide repeats. For example, Huntington's disease is associated with a shorter repeat sequence.

Another benefit of this type of analysis is that it can be successfully used to monitor patients following transplant therapy. It can allow for the prediction of problems associated with transplants, such as graft rejection or a relapse of the disease. This proactive type of testing can significantly aid the patient in obtaining recovery from their condition and transplant surgery.

While there are many techniques to choose from with regards to DNA analysis, STR analysis has many benefits to offer for several different applications. Perhaps most pressing are the concerns regarding the storage of information obtained by STR analysis, which entails databases at local and national levels. Clearly. the ethical aspects of DNA analysis need to be addressed and resolved as techniques such as STR analysis continue to be refined or replaced with more effective and efficient ways of analysing DNA.

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[Add a Comment]
Hello, May I know if there would be any difference in the number of STR Loci used to detect DNA Matches, i.e. would the number be vary with the ethnicity or geography of any individual or species? Or would 13 STR loci suffice for all the people of all the nations in the world?
Aniva - 9-Apr-18 @ 6:37 PM
Hi i am just wondering about the use of STRs in Pre-implantation genetic diagnosis (PGD), how we will be finalizing the group of STRs related to a single gene disorder, like designing primers and all in detail..... thanks
bob - 4-May-17 @ 7:32 AM
Dear Ally, If all the 14 STR loci match son to mom and dad, there is 99.9% cahnce that the dude is the father of this child. Remember the child inherits one allele (at each locus) from each of the parents. Say if dad has alleles 14,15 at locus A and mon has 16,19, the child is expected to have the genotypes 14,16 or 14,19 or 15,16 or 15,19. So for each of the 14 loci you probably tested, there are at most 4 possible genotypes a child can inherit from 2 genotypes (Dad's and Mom's). if there is such a match that at each of the 14 loci, there is one of the 4 possible genotypes, then the child belongs to the alleged father.
Captain F - 26-Apr-17 @ 10:46 AM
Hi if 14str genetics tested father n son share the same..is he da biological father..
Ally - 11-Dec-16 @ 1:04 PM
Rely understood thank you withwonderful presentation
prof - 26-Sep-16 @ 4:51 AM
@Diana. No, sorry this is purely an information based website.
ExploreDNA - 29-Aug-14 @ 2:26 PM
I was wondering if you provide STR analysis of cell lines and what the cost would be. We have human-induced pluripotent stem cells that we would like to be able to match back to the fibroblasts from which they were derived. Thank you, Diana Neely
Diana - 28-Aug-14 @ 10:12 PM
STR is important in dna finger printing a good subject
bill - 12-Jun-14 @ 5:28 AM
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