Selectiemarkers

Selectiemarkers, often called selectable markers in English, are genetic elements that allow researchers to identify cells that have taken up a genetic construct. They are essential in genetic engineering, molecular cloning, and functional genomics because the introduced DNA usually exists in only a small fraction of cells; markers enable selection or screening of those that acquired the DNA.

Types: Selectable markers confer a growth advantage under selective conditions, such as antibiotics or herbicides, so only transformed cells proliferate. Screenable markers do not confer growth advantage but produce a detectable phenotype, enabling later identification.

Common examples: Antibiotic resistance markers such as neomycin resistance (neo), kanamycin resistance (kanR), hygromycin B phosphotransferase (hpt), and puromycin resistance (pac) are widely used in mammalian and bacterial systems. In plants and some microbes, nptII, bar, and hpt serve as selectable markers. Screenable markers include fluorescent proteins (GFP, RFP) and enzymatic reporters such as lacZ.

Applications: Marker genes are carried on transformation vectors alongside the gene of interest. Transformed cells are selected by growth on selective media or by screening assays; once identified, the marker can be maintained, replaced, or removed.

Marker removal and regulatory considerations: For many applications, especially transgenic crops and therapeutic contexts, it is desirable to remove marker genes after selection to reduce metabolic burden and address regulatory concerns. Techniques include site-specific recombinases (Cre/loxP, FLP/FRT) and recombination-based marker excision. Biosafety guidelines govern the use of selectable markers in research and commerce.

Limitations: Marker expression can be silenced; marker burden may affect phenotype; cross-resistance and environmental spread are concerns.