1. 9-3 DNA Typing with Tandem Repeats

2. Repeated Nucleotides
Portions of the DNA molecule contains sequences of bases that are repeated numerous times.

3. Tandem Repeats
These tandem repeats offer a means of distinguishing one individual from another DNA typing.
Tandem repeats. MLVA is a method used to perform molecular typing of microorganisms. It utilizes the naturally occurring variation in the number of tandem repeated DNA sequences found in the microbial genome of most bacterial species. Such tandem repeats may be perfect, but often imperfect repeats containing mutations are encountered.

4. RFLP
Length difference is associated with relatively long repeated DNA strands forms the basis for one of the first DNA typing procedures.
Called Restriction Fragment Length Polymorphisms, (RFLPs)

5. In the first step, purified genomic DNA is digested with one or more restriction enzymes. The choice of restriction enzymes is usually based on the ability to distinguish genetic variability and the cost of the enzymes. The digested fragments are separated by agarose gel electrophoresis and appear as a continuous smear on the gel due to the broad distribution of fragment sizes generated by the enzymes.
To detect the desired fragments, the gel-separated DNA fragments are transferred to a nitrocellulose or PVDF membrane for handling and detection. A labeled single-stranded DNA probe is hybridized to the membrane to identify a subset of fragments. The results are visualized to reveal the unique RFLP fingerprint.
Probes for RLFPs are based on single- to low-copy number sequences in a genome and usually range between 500 and 2,000 bases. Probes are labeled to detect even low amounts of samples and identify the fragments that will become the basis of the fingerprint. The resulting RFLP markers observed are a result of specific probe and restriction enzyme combinations. For example, Probe A and EcoRI-digested genomic DNA will define one RFLP for a specific genome. Probe A and HindIII-digested DNA will define a different RFLP for that genome (Figure 2A). Knowledge of the template sequence, though not required, allows faster development of useful RFLP probes.
RFLPs and restriction enzymes can also be used to detect DNA differences between two individuals. Figure 2B illustrates probe hybridization and detection on a simplistic level, comparing two individuals for HindIII-based RFLPs of two alleles (labeled “1” and “2”). In this example, probe A detects different restriction fingerprints in the two individuals due to loss or gain of a HindIII restriction site on allele 2. In most cases, however, fragment length variability between individuals is a result of insertion or deletion of DNA sequences outside of the restriction sites, caused by natural recombination and replication. RFLP analysis is also used in applications such as genetic counseling, plant and animal breeding programs, and disease monitoring.

6. Restriction Enzymes
In the laboratory, DNA molecules are cut up by a restriction enzyme, and the resulting fragments are sorted out by electrophoresis.

7. Electrophoresis
Materials undergoing electrophoresis are forced to move across a gel loaded plate under the influence of an electrical potential.
Substances such as DNA can be separated and characterize using electrophoresis.

8. DNA Separation
Substances such as DNA can be separated and characterize using electrophoresis.

9. Typical DNA Pattern
A typical DNA fragment pattern shows two bands one RFLP from each chromosome.