Nearly every property of every cell in every
organism is defined by its genes. Genes are
segments of DNA, and DNA can be thought of
as an instruction manual. Your genes are inherited
from your parents, and a mixture of their
genes makes up your genome, or the complete
set of genes present in an organism.
Through breeding and artificial selection,
humans have been selecting for particular
traits or genes in domestic animals and plants,
for thousands of years.
However, this method is extremely inefficient
and is often limited by the natural variation
in a species. Every time that you want to
add a trait to, say, a tomato, you would breed
two varieties, each carrying a different subset
of the desired traits, and hope for the right
combination in one of the offspring. Perhaps,
combining two traits wouldn’t be all that
difficult. However, the chances of a plant
offspring having multiple new, desired traits,
and nothing else, is next to zero. Each generation
takes significant amounts of time to grow
and reproduce so this process is often very
tedious.
Gene editing is a more recent advancement
that allows for more intentional and accurate
changes in the instruction manual or genome,
and consequently, in the organism’s characteristics.
So now, if I know which genes are responsible
for making a tomato redder and larger, I can
simply change the instruction manual directly,
and thus bring these traits to the tomato
plant.
Perhaps, the most popular method of gene editing
is known as CRISPR-Cas9. While it wasn't named
'CRISPR' because it makes genes crispier,
it certainly could be used to edit a plant’s
genome so that its roots, which we would consume
as carrots or radish, would be crispier.
Interestingly, CRISPR was not invented, but
rather, discovered, by trying to figure out
how things work. CRISPR is an integral part
of a natural process (normally used by bacteria
as an ‘immune system’ to protect themselves
against viruses) that scientists have utilized
in order to edit the genetic code of organisms.
Basically, the process has three parts. First,
the guide RNA is essentially responsible for
recognizing which segment of DNA should be
edited. This is analogous to searching for
a particular word that you want to change
in a large document. Next, a Cas9 protein,
that is bound to the guide RNA, cuts the defined
sequence of DNA. This is like deleting the
word that was just found. Finally, template
DNA is used to guide the rebuilding process
of the cut segment to eventually contain the
new DNA sequence that scientists want. This
is like writing a new word where the old word
once stood. There are actually multiple ways
of editing genomes with CRISPR, but for this
video, this method will suffice.
Possibilities with such genome editing technologies
are endless, from making crispier carrots
to curing genetic diseases. However, even
the smartest scientists can not know all the
answers to ethical questions pertaining to
the modification of genomes. For example,
when is it ethical to use such a technology
on humans? What is certain, is that genome
editing will change the world forever.
