VNTRs

Variable numbers of randomly repeated (VNTR) units are one common type of insertion that results in an RFLP. The VNTRs can be inherited, in which case they are useful in estabhshing genetic association with a disease in a family or kindred or they can be unique to an individual and thus serve as a molecular fingerprint of that person. 

Kasai K, Nakamura Y and White R 1990) Amplification of a variable number of tandem repeats (VNTR) locus (pMCTii8) by the polymerase chain reaction (PCR) and its application to forensic science. ] For Sci 35 1196-1200. 

Fuke, S., Suo, S., Takahashi, N., Koike, H., Sasagawa, N., and Ishuiri, S., The VNTR polymorphism of the human dopamine transporter (DAT1) gene affects gene expression, Pharmacogenom. J., 1,152,2001. 

Hutchison, K.E., LaChance, H., Niaura, R., Bryan, A., Smolen, A. The DRD4 VNTR polymorphism influences reactivity to smoking cues. J. Abnormal Psychol. 111 134, 2002. 

Although less common than SNPs, another type of genetic polymorphism is the variable nucleotide tandem repeat (VNTR), also called microsatellite [65]. 

Ethnic variation in allele frequencies can lead to important differences in disease susceptibility, outcome and drug metabolism [68, 69]. In addition to single nucleotide polymorphisms, variable number of tandem repeat (VNTR) regions have been shown to have functional significance. 

RFLP analysis by the Southern blot procedure and detection with probe specific for each VNTR are the basis of DNA fingerprinting. Using just four DNA probes, paternity can be excluded with a cumulative probability of 99.9% (J2). 

Nadeau J, Grabs R, Goodyer CG, Wickramasinghe S, Colle E, Polychronakos C Insulin expression in human thymus is modulated by INS VNTR alleles at the IDDM2 locus. Nat Genet 1997 15 289-292. 

Expansion of repetitive sequences (minisateflites or VNTRs, variable number of tandem repeats) within the DNA... 

Minisatellites-the repeated unit typically ranges from 20 to 70 bp, and the length of the entire repeat may reach 20 kb. This is the class most often referred to as VNTRs and contributes to RFLP patterns on Soulhem blots. 

Answer C. VNTR sequences are amplified using a PCR and analyzed by gel electrophoresis. Although RPLP analysis could potentiaDy be used for this purpose, it is not the method of choice. 

VNTRs (variable number of tandem repeats). These polymorphisms are the result of varying numbers of minisatellite repeats in a specific region of a chromosome. The repeat units typically range in size from 20 to 70 bases each. The repeat is flanked on both sides by a restriction site, and variation in the number of repeats produces restriction fragments of varying size. 

B. in a VNTR, variation in fragment lengths is produced by differences... 

The dopamine D -like receptor polymorphisms include SNPs, variable-number tandem repeats (VNTRs), and splice variants (58,59). The polymorphic forms of the dopamine D receptor, for example, manifest as variable numbers of 48-bp repeat sequences (denoted D j to D., ) (49). 

By contrast, studies of the dopamine D -like receptors have found evidence for the association of the receptor with disease (66) these studies have been replicated (41,42). From among the multitude of these studies, only selected examples are reviewed here. For example, evidence both for and against the association of the dopamine D -like receptors with schizophrenia has been reported. Polymorphisms of the dopamine receptor, including the third intracellular loop VNTR, alter dopamine receptor expression. In addition to association with schizophrenia (3,67-70), the dopamine polymorphisms have been associated with the genetic basis of the variable efficacy of antipsychotics such as clozapine (or neuromuscular toxicity—tardive dyskinesia) (69,71,72). Similarly, promoter SNPs have been associated with altered clozapine efficacy (67,68,73). 

The initial VNTRs were several hundred nucleotide units long requiring extended laboratory periods for the various segments to separate on the gel. Today, most tests employ shorter, 3 5 nucleotides long, VNTRs that allow for more rapid movement on the gel, resulting in faster and less costly results. It also allows for the production of a greater number of sequences that are looked at, and hence a greater ability to match or not match the results. These shorter sequences are called short tandem repeats (STRs). 

Of the other SERT polymorphisms, only the VNTR polymorphism has been investigated for its association with response to antidepressant drugs (Kim et al. 2000). 

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