To make a genetically modified mosquito, Oxitec’s scientists have to find a way of incorporating the new gene into the mosquito’s own DNA, from where it will be copied into every cell of the mosquito’s body.
The process begins with mosquito eggs. These are tiny, cigar-shaped objects – about 1mm long. Using special glass needles, so sharp that the point can only be seen clearly under a high-powered microscope, Oxitec’s scientists can inject very small amounts of DNA into the end of a mosquito egg. The amount of DNA injected into each egg is miniscule – typically around 10 thousand-millionths of a litre!
Many of the eggs injected in this way won’t survive. In others, the DNA which is injected won’t be incorporated into the mosquito’s cells. But in a very few eggs, the new DNA will be taken up by the mosquito’s cells and will be cut and pasted into the mosquito’s own genome. If this happens in the sperm cells of a male mosquito, or the egg-producing cells of a female, the new DNA can be passed on to their offspring.
After being injected, the eggs are hatched, and the resulting mosquitoes carefully looked after until they reach adulthood. Then they are bred with other mosquitoes, and if the injected DNA has entered sperm or egg cells, then it will be passed on to their offspring. The DNA which was injected contains the lethal gene, but it also contains a fluorescent gene which allows the genetically modified mosquitoes to be identified using a special microscope. So Oxitec’s scientists can look at the offspring of the mosquitoes which were injected to identify those which contain the new DNA.
The scientists may have to inject thousands of mosquito eggs to obtain just one individual which has the new DNA incorporated into their genome. But from this single insect, a new strain of genetically modified mosquitoes can be made.