Historically, scientists have been able to
alter the traits of domesticated plants and animals,
but have not been able to do this to wild populations.
Here we use mosquitoes,
as an example to explain why most genome alterations,
designed by humans don't persist in nature
and how a recently proposed technology can change that.
The transgenic mosquito, tinted blue,
has an altered gene inserted into one of its chromosomes.
When it mates with the wild-type mosquito,
each parent contributes one copy of each chromosome to their offspring.
Thus, only 50 percent of offspring will carry the altered gene.
While the other half will inherit the wild-type version from both parents.
Even if the altered gene doesn't reduce
the likelihood of each mosquito surviving and reproducing,
it may persist at a low frequency in the ocean of wild mosquitoes,
or it might go extinct after several generations of especially unlucky inheritance.
This process is what keeps us from altering wild mosquitoes
prevent them from transmitting diseases such as Malaria or Dengue.
Team led by Kevin S. Felt at the WYSS Institute,
the Harvard Medical School and the Harvard School of Public Health,
has now outlined a way to build gene drive,
that can improve the odds that almost any alter gene will be
inherited potentially allowing them to spread through even wild populations.
The proposal relies on the CRISPR/Cas9 system.
A new genome editing technology,
co-developed, by the same researchers at the WYSS.
Gene drive mosquitoes carry both the altered gene,
the genes for the cast nine enzyme and several guide RNA's that tell it where to cut.
When passed to offspring,
the guide RNA is direct Cas9 to cut
the wild-type version of the gene inherited from the wild-type parent.
The cell then copies both the altered gene and the drive when it repairs the damage.
Because the mosquito now has two identical copies,
one on each chromosome,
all of its offspring will inherit the alteration and the gene drive.
This same process will be repeated in subsequent generations
causing the alteration in a gene drive to spread through the population.
