Humans have been altering plants and animals for thousands of years;
we started with a process called "selective breeding" where organisms that expressed
desired traits are bred together to pass on those traits to their offspring.
The result of this breeding is all around you! For example, early farmers bred for
larger and tastier corn by selectively planting only corn kernels that came
from corn that was larger and tastier. As humans learned more about the role of
genes and DNA and trait expression, we started developing new techniques for
alterations. GMOs or genetically modified organisms, are created by introducing a
gene from another organism or a gene that has been modified in a lab.
For example biotechnologists have created varieties of corn that are resistant to
the herbicide Round-up by introducing a modified version of a corn gene.
Recently, scientists have developed a whole new way to alter DNA without introducing new
or modified genes; that tool is called CRISPR-Cas9. Now, scientists can
alter corn to be resistant to Round-up by simply changing the existing genetic
makeup of corn. This is much more efficient and precise than the method of
introducing transgenes. So what is CRISPR ca9?
Cas9 is a protein that comes from bacteria like streptococcus pyogenes and functions as
a defense against viruses. A virus invades of bacterium by inserting its
genetic material into the bacterium's DNA to make more copies of itself. When
infected with a virus, the bacterium stores a small piece of viral DNA so
that the next time the virus attacks it can produce an RNA copy which will guide
Cas9 to the invading viral DNA Cas9 then makes a single
double-stranded cut in the viral genome. Learning from streptococcus, scientists
have been able to take advantage of this precise defense mechanism to create
specific edits to genome. Let's see how this would work if
scientists wanted to change a mouse's fur color from black to white. Scientists
can provide Cas9 with an RNA complement containing the gene they want
to modify, so that Cas9 knows what DNA to look for. Here, our scientist
provides Cas 9 with the RNA complement of the black fur color gene and
inserts it into a mouse embryo. Cas 9 that makes a single cuts in the gene, and
scientists can make a desired mutation in one of two ways. The first way is just
to hope that the edit you want occurs by chance; this works surprisingly well. The
cut ends of the DNA are fairly unstable, and accidental insertions deletions, and
replacements are common. Scientists perform CRISPR in a large number of
organisms, and then screen the organisms for the desired
characteristics. The second way is to provide the organism with a template of
the gene with the desired mutation, so that repair enzymes in the organism can use
the template to make exactly the mutation provided. The embryo is placed
back into a mother to finish development, and is born with white fur. Now that we
understand CRISPR-Cas9, we can envision a myriad of potential
applications. Gene therapy could be done in embryos, so that babies grow up
without ever experiencing a disease. Gene therapy could also potentially be done
in adults through edits to stem cells, which are cells that can develop into
any of the specialized cells in the body under the right conditions. Genetic
diseases such as sickle-cell and cystic fibrosis could be prevented. Researchers
are also experimenting with a new application of CRISPR to achieve gene
drive, a mechanism that ensures both chromosomes in an organism received the
same edit so that all of their offspring, and all their offspring's offspring
inherit the mutation, with the goal of forcing that mutation to all members of
a population. For example, researchers could eliminate malaria using gene Drive
in mosquitoes CRISPR is the most powerful gene- editing
tool ever seen to date, but it is still in a highly experimental phase. There are
no fully developed laws regulating CRISPR, and there are many concerns about
both its practical and moral consequences. As technology continues to
advance, researchers, lawmakers and the public will have to decide how to
properly use CRISPR.