Overview.
Germ line Cells.
Gene drive.
Gene drive is a technology, which is used along with CRISPR.
CRISPR is a gene editing technology.
Inheritance involves getting one set of chromosomes, from each parent.
50% of the genes, of a new born, comes from the father,
and 50% from the mother.
If we alter the genes, of one parent, using CRISPR,
there is a 50% probability, that the offspring will inherit the altered gene.
Certain species of mosquitoes carry the malaria micro-organism.
These mosquitoes transmit the infection, from one human being to another.
Over a period of time, a large proportion of the human population, can get infected.
Malaria is a wide spread disease, in many countries.
Scientists have discovered a method, to genetically alter the germ line cells of the mosquito,
such that it is unable to carry the malarial parasite.
This can be done in the laboratory for small set of mosquitoes.
The intention is to spread this genetic trait, to most of the population in a region.
When these mosquitoes are released into the wild,
they mate with other mosquitoes.
50% of the offspring will inherit this trait.
50% of their offspring will inherit this trait.
Over many generations only a small segment of the population,
will inherit the trait, of being unable to carry the malarial parasite.
This does not achieve the objective, of spreading the trait,
to most of the mosquito population.
The gene drive technology, which was developed recently,
overcomes this limitation.
Our body comprises of mostly somatic cells.
There are some 200 types of basic cells,
called stem cells, which generate somatic cells.
Somatic cells make up tissues.
Tissues make up the organs in our body.
When we make genetic changes, in the somatic cells,
it will impact only the target tissue and organ.
The altered genetic trait, will impact only the target organism.
The trait will not be inherited by future generations.
The sperm cells of the male, and egg cells of the female,
are involved in reproduction.
These are called germ line cells.
If we genetically alter the gene cells in these cells,
the altered genes can get carried forward, to future generations.
In the case of the malarial parasite carrying mosquito,
the intention is to genetically disable this function,
in most of the mosquito population.
It is not practical to directly alter the genes of the entire mosquito population,
in the laboratory.
If we alter the germ line cells, of some mosquitoes,
and let them out in the wild, they will mate with other mosquitoes.
Future generations have a 50% probability of inheriting the modified gene.
Over many generations this trait could spread to a section of the population.
To enable this trait to spread to most of the population,
a new technology called gene drive has been developed, by scientists.
CRISPR technology uses the guide RNA and the Cas9 protein,
to modify the gene.
In the case of gene drive, the complex has some special additional RNA.
The complex encodes the editing machinery within it.
This is used to modify the germ line cells, of the target organism.
One powerful example, for using gene drive, is the malaria carrying mosquito.
The female of the anopheles mosquito species, carries the malaria parasite.
When it bites human beings it infects them with this parasite.
When a mosquito bites an infected person, it carries and transmits the parasite,
to other humans.
This causes the disease to become wide spread.
It is now possible to alter the germ line genes, using gene drives.
This can be done in the laboratory.
Gene drive altered mosquitoes, are released to the wild,
to mate with other mosquitoes.
They pass on the gene drive to the offspring.
The offspring will have one copy of the wild DNA,
and one copy of the gene drive DNA.
To start with, it is heterozygous,
that is the alleles of the genes will be different.
The gene drive has special guide RNA which directs the Cas9,
to cut the wild type version, inherited from the wild type parent.
It then copies both the altered gene, and the drive to the wild type copy.
Now the mosquito is carrying the gene drive in both its copies.
Now it becomes homozygous.
Because the mosquito has now two identical copies, or alleles,
in both the chromosomes, all of its offspring will inherit the alternation.
This is repeated over and over again, in subsequent generations.
This can potentially spread to whole population of mosquitoes.
If implemented properly, it can eliminate malaria carrying mosquitoes,
in the entire region or country.
Gene drives are a potentially powerful technology,
to alter an entire species of sexually reproducing organisms.
It is specially effective in fast reproducing organisms, like mosquitoes.
If we release one gene drive mosquito,
for every ten thousand wild type mosquitoes,
in about 16 generations the whole population will inherit the trait.
Inserting about 1% of the population with gene drive,
has the potential to spread the trait to the entire population.
Gene drives have the potential to be used, for the benefit of mankind.
There is a possibility that this technology can be misused.
Scientists are building safe guards, to avoid misuse of this technology.
They have succeeded in producing genome edits,
which can be blocked or reversed with other gene drives.
Though we took malaria for example, many other diseases,
are also carried by mosquitoes.
This technology can be used for other species also.
Hopefully in the future, we will find CRISPR and gene drive being used,
for the benefit of mankind.