Marker gene

A marker gene is a gene used in nuclear biology and molecular biology to determine if a nucleic acid sequence has been successfully inserted into an organism's DNA. There are two types of marker genes: a selectable marker and a marker for screening.

A selectable marker protects the organism from a selective agent that would normally kill it or prevent its growth. In a transformation reaction, depending on the transformation efficiency, only one in a several million to billion cells may take up DNA. Rather than checking every single cell, scientists use a selective agent to kill all cells that do not contain the foreign DNA, leaving only the desired ones.

Antibiotics are the most common selective agents. In bacteria, antibiotics are used almost exclusively. In plants, antibiotics that kill the chloroplast are often used as well, although tolerance to salts and growth-inhibiting hormones is becoming more popular. In mammals, resistance to antibiotics that would kill the is used as a selectable marker.

A screenable marker will make cells containing the gene look different. There are three types of screening commonly used:

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