Polymorphic markers

The disease-causing mutation(s) does not need to be identified. We need identify only a closely linked marker polymorphism. 

Although the physiological role of P-glycoprotein is not fully understood, it is conceivable that transporter proteins, such as P-glycoprotein, prevent intracellular accumulation of potentially toxic substances and metabolites (69). Because the exposure of epithelial cells depends on the entry and efflux of xenobiotics via transporter proteins, it is plausible to hypothesize that genotype-dependent P-glycoprotein expression may contribute to a certain disease susceptibility. This may either indicate that MDR1 as marker polymorphism causes disease or that this marker is closely linked to a disease locus. 

DNA marker—polymorphic locus that is easily assayed, yielding reproducible results. 

Fig. 3. Homologous chromosomes having evenly spaced genetic markers (1 9). The segregation of the or quantitative trait loci (QTL) can be followed using marker 2. Polymorphisms within marker 2 can be used to foUow the segregation of the genes within the QTL, even though the exact location or...

Other regions of the genome (s), such as repetitive elements (see later), also evolve rapidly and can be exploited as polymorphic markers in random or selective PCR assays. Characterization of such markers is of significance... 

Tautz, D. (1989) Hypervariability of simple sequences as a general source for polymorphic DNA markers. Nucleic Acids Research 17, 6463-6471. 

Williams, J.G.K., Kubelik, A.R., Livak, K.J., Rafalski, J.A. and Tingey, S.V. (1990) DNA polymorphisms amplified by arbitrary primers are useful as genetic markers. Nucleic Acids Research 18, 6531-6535. 

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