DNA tests

DNA tests

1. RFLP(restriction fragment length polymorphism) analysis

2. PCR(polymerase chain reaction) analysis

3. STR(short tandem repeats) analysis

4. Y-chromosome analysis

5. Mitochondrial analysis

 

1. RFLP(restriction fragment length polymorphism) analysis

Restriction Fragment Length Polymorphism (RFLP) is a difference in homologous DNA sequences that can be detected by the presence of fragments of different lengths after digestion of the DNA samples in question with specific restriction endonucleases.

An RFLP probe is a labeled DNA sequence that hybridizes with one or more fragments of the digested DNA sample after they were separated by gel electrophoresis, thus revealing a unique blotting pattern characteristic to a specific genotype at a specific locus. Short, single- or low-copy genomic DNA or cDNA clones are typically used as RFLP probes.

Original page:

http://www.ncbi.nlm.nih.gov/projects/genome/probe/doc/TechRFLP.shtml

 

How It Works

 

SNPs or INDELs can create or abolish restriction endonuclease (RE) recognition sites, thus affecting quantities and length of DNA fragments resulting from RE digestion.

Original page:

http://www.ncbi.nlm.nih.gov/projects/genome/probe/doc/TechRFLP.shtml

Original page:

http://www.ncbi.nlm.nih.gov/projects/genome/probe/doc/TechRFLP.shtml

Screening for a RFLP "marker"

The pedigree shows the inheritance of a RFLP marker through three generations in a single family. A total of 8 alleles (numbered to the left of the blots) are present in the family. The RFLPs of each member of the family are placed directly below his (squares) or her (circles) symbol and RFLP numbers.

 

Original page:
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/R/RFLPs.html

 

2. PCR(polymerase chain reaction) analysis

The polymerase chain reaction (PCR) is a scientific technique in molecular biology to amplify a single or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence.

 

Diagram of PCR reaction to demonstrate how amplification leads to the exponential growth of a short product flanked by the primers.

 

Original page:
http://en.wikipedia.org/wiki/Polymerase_chain_reaction

3. STR(short tandem repeats) analysis

A short tandem repeat (STR) in DNA occurs when a pattern of two or more nucleotides are repeated and the repeated sequences are directly adjacent to each other. The pattern can range in length from 2 to 5 base pairs (bp) (for example (CATG)n in a genomic region) and is typically in the non-coding intron region.

STR analysis is a relatively new technology in the field of forensics, having come into popularity in the mid-to-late 1990s. It is used for the genetic fingerprinting of individuals.

 

 A partial human STR profile obtained using the Applied Biosystems Identifiler kit.

Original page:
http://en.wikipedia.org/wiki/Short_tandem_repeat

 

4. Y-chromosome analysis

Several genetic markers have been identified on the Y chromosome that can be used in forensic applications. Y-chromosome markers target only the male fraction of a biological sample.

Because the Y chromosome is transmitted directly from a father to all of his sons, it can also be used to trace family relationships among males.

 

Original page:
http://www.dna.gov/basics/analysis/ychromosome

 

5. Mitochondrial analysis

Mitochondrial DNA (mtDNA) analysis allows forensic laboratories to develop DNA profiles from evidence that may not be suitable for RFLP or STR analysis. While RFLP and PCR techniques analyze DNA extracted from the nucleus of a cell, mtDNA technology analyzes DNA found in a different part of the cell, the mitochondrion. Old remains and evidence lacking nucleated cells--such as hair shafts, bones, and teeth--that are unamenable to STR and RFLP testing may yield results if mtDNA analysis is performed.

It is important to note that all maternal relatives (for example, a person's mother or maternal grandmother) have identical mtDNA. This enables unidentified remains to be analyzed and compared to the mtDNA profile of any maternal relative for the purpose of aiding missing persons or unidentified remains investigations.

 

Original page:
http://www.dna.gov/basics/analysis/mitochondrial