Evoluti̇on of eye & Pigmentation

1. EVOLUTION OF EYE
&
PIGMENTATION
MESUT AKPUNAR

2. EyesEyes
 The eye is an organ for
sensing light
 About 97 percent of the
animals known have eyes
 More complex eye includesMore complex eye includes
sense of vision, color, motionsense of vision, color, motion
and textureand texture

3. 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

4. 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)

5. 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

6. Evolution of the eyes (II)
 The patch gradually invaginates into a cup
Planarium has maintained the structure of cup
eyespots

7. 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

8. 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

9. Evolution of the eyes (V)
 Cornea
and
 Lens formation

10. Evolution of the eyes (VI)
 More complex eyes give the full sense of vision,
including color, motion, and texture

11. Evolution of eye base on
special gene and unit
PAX-6
Opsin

13. Swich off Pax-6 gene in drosophila and mice
eyeless
Small eye
http://www.img.cas.cz/resrep/zk/mouse-eye.html

14. head wing
antenna paw
Pax-6 gene expression in different body
region
Halder et al., 1995

16. 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

17. 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.