Single Nucleotide Polymorphisms

The sequence polymorphisms found within the mitochondrial DNA are termed single nucleotide polymorphisms (SNPs). Single nucleotide polymorphisms are positions within the genome where there is a difference between people at one single base. It may be that at a particular position the nucleotide ''A'' is normally found, but in a minority of people the base ''G'' is present. In such an instance most people will have the base pair A/T with a minority being G/C at the same position. There are a number of SNP sites on the mitochondrial DNA within the loci examined. Single nucleotide polymorphisms were first used in forensic science by the U.K. Forensic Science Service to examine mitochondrial DNA from suspects and from crime scenes.[9] This method examined 12-point mutations known to be variable within the mitochondrial

DNA by a technique termed minisequencing. Minise-quencing of the mitochondrial DNA polymorphic sites allows rapid screening of the variable DNA bases. In forensic investigations this process is used to exclude all the samples in a case that do not match at the 12 points. An example of an SNP of mitochondrial DNA is shown in Fig. 1.

Detection of SNP by minisequencing requires separation of DNA fragments by either gel or capillary electrophoresis. Much SNP testing for forensic and diagnostic purposes can now be performed using oligo-nucleotide microarrays.[10] Microarrays (also covered in Chapter 10 of this encyclopaedia) allow the single-base difference to be detected on a silicone chip. The two different versions, either A or G in the case example, are placed on the chip. If A is present then a DNA sequence with T will bind. If G is present a DNA sequence with C will bind. It is possible to detect SNP polymorphic sites on the mitochondrial DNA. An example is shown in Fig. 2.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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