RFLP and Genetic Screening

PCR Analysis of the Cystic Fibrosis Gene

Linked DNA Markers

Study Questions

Molecular Markers WWW Links

Genetic Topics

Linked DNA Markers

All of the DNA (RFLP or PCR) markers that we have discussed so far have been targeted to a specific gene. For many important traits, the actual gene of interest is not known. Therefore, probing for the presence of the normal or mutated allele is not possible. Instead the probe recognizes a sequence that is close to the actual gene of interest. The only drawback to screening with a probe that is near, but not actually in the gene, is that an error in diagnosis can occur if a recombination event occurs between the marker and the actual gene of interest. The error is directly proportional to the distance that the marker is from the gene.

The following illustration shows the relationship between two markers and a gene.

Marker 1

       1 cM
   Gene    Marker 1
     |        |

Marker 2

               5 cM
   Gene                    Marker 2
     |                        |

Recombination is less likely to occur between marker 1 and the gene than between marker 2 and the gene. Actually there is only a 1% chance the linkage between marker 1 and the gene will be broken. For diagnostic purposes 99% of the time the individual with marker 1 will have the specific allele of the gene of interest. Marker 2 is 95% accurate in diagnosing the specific allele at the gene of interest. Obviously, the closer the marker is to the gene the more accurate the testing procedure. But the best probe still is one that actually hybridizes to the particular gene that is in question.

Copyright © 1997. Phillip McClean