Re: Why are fruit fly eyes red?

Dear Marion,

Thanks for your question about fruit flies. You've come to the right place 
for an answer. As a matter of fact, I am a scientist who studies fruit 
flies in a laboratory all day long. We study the development of the fruit 
fly's eye. More importantly, I study the development of pigment cells 
in the eye.

That's right; the eye is made up of two different types of cells. There are 
cells that are sensistive to light and there are pigment cells that give 
the eye its distinctive color. Neither type of cell is much good without 
the other.

There are actually two types of pigment in the eye of the fruit fly. The 
first kind is a rusty-colored pigment called ommachrome pigment. The second 
is the reddish pigment, called pteridine, which gives the eye its bright 
red color. These pigment molecules are not unlike the pigment that we have 
in our skin or our hair or our eyes, for that matter. Pigment molecules 
provide color to various tissues in the body.

Why are pigment molecules important? The pigment in a fly's eye acts as 
insulation so that incoming rays of light are focused on the photoreceptor 
cells. The optical insulation prevents light rays from scattering when they 
enter the eye. The result is clearer vision for the fly.

Finally, there are actually flies that have a mutation that inhibits the 
production of pigment in the eyes. These flies have white eyes, kind of 
like an albino animal that has no pigment in its skin. As scientists, we 
like to learn about mutations like that. Learning about mutations in fruit 
flies and other animals helps us to learn more about mutations in humans 
that can cause a variety of diseases.