NCLC-120
Extra Credit
Synopsis Prompt Questions
for LLOG 6:
1) 1. How does evolutionary theory explain the development of human eyes? (Start with a two-cell eye, and include an explanation of the role of the Pax-6 gene.)
In a
two-cell eye, there are photoreceptor and pigment cells. This is the
most basic
form of an eye. Today, you can find this type of an eye in larvae of
ragworms.
This type of an eye would typically be cup-shaped. The job of the most
basic
form of an eye is to detect light. The Pax-6 gene is a tool-kit
protein, which
means that it helps with building cell types. In this case, the Pax-6
gene is
building the parts of the eye, such as the surrounding tissue. In a
two-cell
eye, the eye is shaped like a cup. As time went on, the eye evolved
into a more
complex cone shape because a constricted opening for a light source
created
better vision. The next part that evolved onto the eye was the lens,
which
helps create a sharper image. Now, there are three main types of eyes
called
camera, mirror, and compound eyes. Arthropods have more rhabdomeric
eyes, while
we humans have a ciliary eye. The main difference is that in a ciliary
eye,
there is more membrane surface area and the receptor area has the image
of a
bunch of stacked discs.
Carroll
would respond with this answer: The eye developed based on what was
beneficial
to the certain species. In a certain species, the eye started out
cup-shaped.
However, within those genes, there are switches which control the
modification
of tool-kit genes. The cause of the differences in eyes is because of
these
switches. That is why the development of the eye can relate to the
development
of differences in fruit fly wings in a certain way. Also, because there
is a
modification in the certain tool-kit gene, mainly the Pax6 gene, this
means
that certain changes may have occurred to help build the eye when
certain
switches were not on. However, the switches are meant to be separate so
that it
does not affect the modification of other tool-kit genes throughout the
body. All
of these characteristics kept being passed on, which is why the eye
developed
the way that it did. This also developed through the findings of Evo
Devo.
3) 3. What are tool-kit proteins? How are they different from proteins such as hemoglobin?
Tool-kit
proteins are the proteins that help with the building of cellular
blocks which
are part of a bigger structure. Tool-kit proteins build a structure,
but
certain proteins carry out other processes. Certain proteins such as
hemoglobin
transfer certain messages or necessary items like oxygen. Tool-kit
proteins
also have the ability to build full organs with their full structures.
Unfortunately, other types of proteins can also carry diseases like
sickle-cell
anemia. Overall, tool-kit proteins control every characteristic of
certain cell
types through the body. Other proteins serve the purpose of assisting
in immune
response and cell signaling. It all depends on what the body needs.
Tool-kit
proteins just happen to be the proteins that assist in building organs
because
that is something that the body needs. If the body needed something
else, a
different protein would be formed to relay that message to other
specified
parts of the body.
Most Challenging Concepts
If the evolution of the eye, as Carroll explained, just kept improving the shape of the eye as time went on, why do so many people in the world have eyesight problems? There are more people going blind from certain causes, and there are many people that wear glasses. Shouldn’t every human being have really good eyesight? If the making of the eye has lasted for so many years, shouldn’t the code for a perfect eye keep being passed on through reproduction instead of so many people having eye problems?
Seminar Questions