Short Tandem Repeats (STR) and Variable Number Tandem Repeats (VNTR) By: Jana Wolskij, Zach Walker, Bill Brock, Keaton Rye

Short Tandem Repeats A Short Tandem Repeat is a short sequence of nucleotides that are repeated and are directly adjacent to each other (usually 2-6 base pairs long). The method of STR uses the polymorphic regions that have short repeated sequences of DNA. STRs are found surrounding the structural center of chromosomes (Chromosomal Centromere) Short Tandem Repeats have become one of the most widely used genomic markers for identification and genetic mapping. STRs are most beneficial for human identification

Human Identification STRs are used for human identification What happens is every person gets a copy of each of their parents STR. Since STRs can have many different patterns, it helps with determining the identification of people . Also people have all different numbers of repeats, it is also used to determine an individual. Also in smaller quantities of DNA and in disintegrating DNA, STRs are still able to help pick up the information and type the DNA. In 1996, The FBI has establish 13 specific STR loci (position of a gene on a chromosome) to serve as a standard set for CODIS (FBI Combined DNA Index System). This is to ensure that all forensic laboratories can establish a uniform DNA database, and so that they can share forensic information.

Testing STRs Capillary electrophoresis works by electrokinetically injecting DNA fragments into glass tubes filled with polymer. The DNA is pulled by an electric field, separating them into small fragments. They are then detected by fluorescent dyes that attach to primers in PCR. Sizes are assigned using a labeled DNA standard, which is compared to an allelic ladder. You can also use Gel electrophoresis, and it does pretty much the same thing, except a polyacrylamide gel is use to separate the DNA fragments A picture of what most of the test result would look like. This is from a STR lab kit. 

VNTR Stands for Variable Number Tandem Repeat. It’s the sequence of the genome (which is the entire hereditary structure of the organism) that repeats. They can often be found on chromosomes and the variations in length make it possible for differences between people to be found. It can also be used to connect children to their parents. There are two ways to analyze VNTR data. Identity Matching: both VNTR alleles from a specific location must match. If two samples are from the same individual, they must show the same allele pattern. Inheritance Matching: the VNTR alleles must follow the rules of inheritance. In matching an individual with his parents or children, a person must have an allele that matches one from each parent. If the relationship is more distant, such as a grandparent or sibling, then matches must be consistent with the degree of relatedness.

VNTR VNTR has recently been used for forensic work. Because it produces genetic marks that are specific to each person, it works with the CODIS system that forensic specialists use for fingerprinting. The size of the sequences are measured by gel electrophoresis They make up 40% of repetitive DNA…hence the satellite class There are two different types of VNTR. Microsatellites and Minisatellites Microsatellites are sequences less than five base pairs in length. Minisatellites are sequences more than five base pairs in length. Microsatellites are sometimes confused with STRs

Sources Page DNA STR: http://www.forensicdnacenter.com/dna-str.html Background Information on STRs: http://www.cstl.nist.gov/div831/strbase/intro.htm DNA.gov: http://www.dna.gov/basics/analysis/str STRbase: http://nar.oxfordjournals.org/cgi/content/full/29/1/320 Human identify testing: http://mrw.interscience.wiley.com/emrw/9780471142904/cp/cphg/article/hg1408/current/abstract Genetic Fingerprinting: http://en.wikipedia.org/wiki/Genetic_fingerprinting