EVOLUTION OF EYE&

PIGMENTATION

MESUT AKPUNAR

EyesEyes

The eye is an organ for sensing light

About 97 percent of the animals known have eyes

More complex eye includes More complex eye includes sense of vision, color, motion sense of vision, color, motion and texture and texture

Evolution of the Eye

• To go from nothing to an eye would be a very big jump

• Darwin proposed a series of what appeared to be relatively small steps (they are still gigantic leaps) that might be able to produce an eye

Proto - eye

Eyes appeared around 500 m.y.a. but their complete evolution possibly took just a few million years

Proto-eye is a very primitive eye .

photonElectric signal photon(to CNS)

Evolution of the eyes (I) Early eyes were formed by patches of photoreceptive cells,

called eyespots

Unicellular euglena has maintained this kind of rudimental eyes

Evolution of the eyes (II)

The patch gradually invaginates into a cup

Planarium has maintained the structure of cup eyespots

Evolution of the eyes (III) This kind of eyes is

thought to have developed during the Cambrian

period

The primitive nautilus eye functions similarly to a pinhole camera

Evolution of the eyes (IV)

This kind of eye has a structure that makes it functional in and out of water

Ability of filterin colors, blocking of UV radiation and higher refractive index are increased

Evolution of the eyes (V)

Cornea and

Lens formation

Evolution of the eyes (VI) More complex eyes give the full sense of vision,

including color, motion, and texture

Evolution of eye base on special gene and unit

PAX-6 Opsin

Swich off Pax-6 gene in drosophila and mice

eyelessSmall eye

http://www.img.cas.cz/resrep/zk/mouse-eye.html

head wing

antenna paw

Pax-6 gene expression in different body region

Halder et al., 1995

Evolution of eye color

• Eye color is a polygenic trait• Color is determined by amount and

types of pigment (Melanin)• Lighther skin and hair have lower

melanin so lighther color of eyes• OCA2 gene controls the amount of

melanin

Albinism Extremely low quantities of melanin Severe form of albinisms may appear

red eye

Blue eyes contain low amounts of melanin within the iris. Blue eyes are most common in Northern Europe and Central Europe and to a low rate in Southern Europe (e.g;Spain and Portugal , where 1-49% of the people are blue-eyed, through migration of Northern European and Central European settlers) and Southern Central Asia ; Afghanistan and Pakistan also found in North Africa, West Asia, and South Asia.

This is the most dominant color in humans.In humans, brown eyes contain large amounts of melanin within the iris stroma.Brown eyes are most common in East Asia Southeast Asia, Oceania, Africa, South America and the Middle East

Moderate amounts of melanin and probably represent the interaction of multiple variants within the OCA2 gene. Green eyes are commonly found in Northern and Central Europe. In Iceland 89% of women and 87% of men have either blue or green eye color.

These  color eyes have less melanin than blue eyes.Gray eyes exhibit small amounts of yellow and brown color in the iris. Gray eyes are most common in European, Russia, Sweden, Finland and the Baltic States.