Brief Introduction to Short Tandem Repeats
Microsatellite DNA, also known as short tandem repeats (STR) or simple repeat sequences (SRS or SSR), is widely found in prokaryotic and eukaryotic genomes, consisting of a unit of two to thirteen nucleotides repeated hundreds of times in a row on the DNA strand which is about 5% of the eukaryotic genome, the basic unit (core sequence) is 1-6bp. The most common of these is (CA) n and (TG) n, and the human genome has about 5 × 104 ~ 1 × 105 (CA) n repeats which take 10% of the genome. Each microsatellite DNA has the same core sequence structure, the number of repeating units is about 10 to 60 times, and its length is generally not more than 300bp, mostly located in the non-coding region of the gene, intron or untranslated region. which may be present in the Alu sequence or Satellite sequence, but in the coding sequence and exon also can find the presence of microsatellite DNA.
The high polymorphism of microsatellite DNA is mainly due to the difference in the number of tandem numbers. There is a big difference in the distribution for microsatellite DNA in different races and populations due to the number of repeat units and repetition, which constituted STR genetic polymorphism. And the number of repetitions between different individuals at a homologous STR site is also different so that STR loci analysis can identify individuals that are similar to fingerprint recognition. It is possible to create a personal gene file by identifying a specific sequence of genomes at particular loci. Currently, there are more than 10,000 STR loci are available. STR analysis has become an important analytical method for individual identification and paternity testing in the field of forensic science. It can be applied to judicial case investigation, that is, genetic fingerprint analysis.
The Causes of STR
The replication slip caused by mismatches between DNA strands during the mitotic process is considered to be the most common cause of the occurrence of STR, and in general, there will be an average of one-thousandths of microsatellite DNA will undergo replication slippage. The study showed that the rate of tandem duplication at repeat sequences was higher than the probability of point mutations occurring elsewhere in the genome. Most of the replication slides only cause a change in the repeat unit, and the probability of replication slip is different due to the size of the different copy units and different species.
STR Detection Method
STR analysis is one of the most useful methods in molecular biology which is used to compare specific loci on DNA from two or more samples. There are two common methods for STR detection: capillary electrophoresis (CE) and gel electrophoresis, which can be used to determine the specific amount of microbes Satellite sequence and draw the STR map. Typically, each allele is shared by about 5-20% of people. And the advantages of STR analysis will be reflected in the simultaneous identification of multiple STR loci. Each individual can be identified accurately by the resulting STR map. In theory, if there were 16 STR loci being used in combination, the recognition rate will be 0.999999999998.
The Importance of STR Analysis
It is still common for cell lines to be misidentified and cross-contamination, although scientists use a variety of traditional methods to identify cells, there are still dozens of cross-contamination happened. And even some researchers found that cell lines were misidentified or cross-contamination while cell identification reports for the higher score study articles publication, resulting in erroneous conclusions. All of which will lead to the waste of research funding and time, and resulting in a large number of invalid or erroneous data that will mislead other researchers. Based on the statistics data, around 20% of the cell lines were misidentified and cross-contamination in the labs so that it is a serious concern for researchers to provide accurate cell line identification and prevent cell lines from cross-contamination. Currently, several STR loci have been developed to analyze cross-contamination and cell types at the same time, that can detect up to 0.1 ng of DNA (about 15 Diploid genomes) with high sensitivity for the trace pollution.
All the mentioned above is the complete guide for the Short Tandem Repeat and its importance!