Genes marker

Methods of DNA manipulation now make it possible to insert DNA into prokaryotic, eukaryotic, or viral hosts, creating versatile marker systems that allow as- sessment of the survival and spread of strains, studies on gene transfer, and determinations of cell activity. A potential marker gene must be absent from the strain used in the study, and either absent or in sufficiently low abundance in the microbial population under study to allow detection of marked cells at an appropriate level. 

DNA construct will often contain an effect gene and a selectable marker gene (such as antibiotic or herbicide resistance), both of which are bracketed by promoter and terminator sequences. A plasmid vector carries this cassette of genetic information into the plant genome by one of the above methods. 

Figure 19 Sample gel of the results of a PCR. Lane 1 is a 100-bp molecular marker lanes 2-6 are samples. The presence of the top bands (the species-specific endogenous gene) demonstrates that the PCR amplification was successfiil. Lack of the middle band (the introduced effect gene) and the bottom band (the selectable marker gene) in lane 3 indicates that sample is negative for the effect gene. Presence of all three bands in the remaining lanes indicates the samples are positive for the effect gene...

The plant sample in lane 6 is also positive for the transgene of interest. Because the band for the effect gene (middle band) is typically fainter than the band for the selectable marker gene (bottom band), it appears that for lane 6, the PCR product amplitication for the effect gene is below the assay detection threshold. Because the selectable marker is clearly present and the PCR amplitication worked, lane 6 can be interpreted as a positive result for the transgene of interest. 

Higher expression levels were associated with the encapsulated DNA than with the administration of naked DNA in vitro, but standard liposomal transfection yielded the highest level of gene expression. In vivo, however, the encapsulated DNA exhibited higher levels of sustained expression of a marker gene at 28 days, than that associated with naked DNA or DNA delivered with liposomes. Thus, this study indicated the potential for DNA encapsulated in degradable nanospheres to elicit sustained gene expression in vivo. 

Tab. 16.1 N ovel marker genes that avoid the use of potentially toxic antibiotics, herbicides and drugs for the selection of transgenic plants. ESR1, enhancer of shoot regeneration 1 CKI1, cyto-...

Marker gene Prod uct /phenotype Sources Selective agent Reft... 

Transposon-mediated repositioning and segregation Simple crossing procedure. Independent co-integration not required Depends on transposons to separate transgenes and marker genes. Generates transposon footprint 38... 

Mark I submarine power plant, 17 590 Marker genes, 12 462 plant, 12 486... 

Ap(R) This selectable marker gene is for the resistance of ampicUlin (beta-lactamase), which degrades penicillins to enable selection of the desired DHFR vector. 

Association studies have proven to be more fruitful. In such studies, the allelic frequencies for specific marker genes are compared with a control population. When OCD patients were investigated for the association of tics with the dopamine receptor 2 marker it was shown that there was an increased frequency of homozygosity for the allele A2 of TaqIA at the D2 receptor locus. Not all investigators could replicate this finding however. No positive associations have been found between OCD and the D3 gene while there was some association found between OCD with tics and the D4... 

---