The Department of Conservation has set a target for New Zealand to become pest free by 2050. This includes mice, rats, stoats, rabbits and possums. This is very unlikely to be achieved using the conventional methods of poisons, diseases, traps, shooting or other such methods. 

Previous posts have described the use of genetic drives to control pest populations (Trojan Female Technique) and CRISPR global gene drives. 

However, as Kevin Esvelt explains:  "the problem with current CRISPR-based gene drive systems is that they can spread indefinitely. That means releasing a handful of organisms could eventually affect every population of the target species throughout the world. It's unclear how these systems can be safely tested.

Standard drive systems spread indefinitely because a single piece of DNA encodes the desired alteration, the CRISPR system, and instructions to cut the original DNA sequence. In cells that produce sperm or eggs, CRISPR cuts the original version, causing the drive construct to be copied in its place. All of the organism's offspring will inherit a copy, editing will happen again in the offspring, and the process repeats until the drive system has spread through most or all of the population.

In daisy-chain drive systems, the CRISPR components are split up and scattered throughout the genome so that none of them can be copied on its own. Though physically separated, they're functionally arranged in a linear daisy-chain: element C causes element B to drive, and element B causes element A to drive.

Element C doesn't drive, so its abundance is limited by the number of daisy drive organisms released.  Natural selection will gradually eliminate C from the population. That means B will initially increase in abundance, then decline and vanish. In turn, A will increase even more rapidly, but eventually will run out of B and disappear -- as explained in the video above."

For more on Daisyfield Gene Drive Systems

A Community Meeting to discuss Daisy Drive Technology is being held in Dunedin, New Zealand on September 17th, 2017 at which Kevin Esvelt is the keynote speaker. More about this event after the 17th.