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Eye Color Inheritance

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by

Brook Carlsen

on 23 October 2014

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Transcript of Eye Color Inheritance

Another with possible central heterochromia...
There is no blue pigmentation either in the iris or in the ocular fluid. Dissection reveals that the iris pigment epithelium is brownish black due to the presence of melanin. Unlike brown eyes, blue eyes have low concentrations of melanin in the stroma of the iris, which lies in front of the dark epithelium. Longer wavelengths of light tend to be absorbed by the dark underlying epithelium, while shorter wavelengths are reflected and undergo Rayleigh scattering. Again, this is what makes the sky blue.
Blue Eyes
Eye Color Inheritance
In 2008, new research suggested that people with blue eyes have a single common ancestor. Scientists tracked down a genetic mutation that leads to blue eyes, suggesting all humans originally had brown eyes. Those scientists concluded that the mutation may have arisen in a single individual probably living in the northwestern part of the Black Sea region 6,000–10,000 years ago. A genetic mutation affecting the OCA2 gene in our chromosomes resulted in the creation of a 'switch,' which literally 'turned off' the ability to produce brown eyes. Rather than completely turning off the gene, the switch limits its action, which reduces the production of melanin in the iris. In effect, the turned-down switch diluted brown eyes to blue.
Why Different Colors?
A 2002 study found the prevalence of blue eye color among the white population in the United States to be 33.8% for those born from 1936 through 1951, compared with 57.4% for those born from 1899 through 1905. As of 2006, one out of every six people, or 16.6% of the total population, and 22.3% of whites, have blue eyes. Blue eyes are continuing to become less common among American children. Some believe blue eyes may disappear altogether in thousands of years, while others believe blue eyes may
seem
to disappear, but they will simply hide behind more dominant colors and will reappear only seldomly.
Prevalence
Josie M.'s
Can you guess whose pretty eyes these are?
Green Eyes
Green eyes are most common in Northern and Central Europe. They can also be found in Southern Europe, West Asia, Central Asia, and South Asia. In Iceland, 89% of women and 87% of men have either blue or green eye color. Among European Americans, green eyes are most common among those of recent Celtic and German ancestry, about 16%.
Who am I
with true, green eyes?
As in the case of blue eyes, the color of green eyes does not result simply from the pigmentation of the iris. Rather, its appearance is caused by the combination of an amber or light brown pigmentation of the stroma, given by a low or moderate concentration of melanin, with the blue tone imparted by the Rayleigh scattering of the reflected light.

Blue + Yellow = Green
Brown Eyes
Dark brown eyes are dominant in humans. In many parts of the world, it is nearly the only iris color present.
Prevalence
How about this one?
No one really knows what makes hazel eyes. Some researchers guess that hazel is simply a combination of brown and green eyes. Others guess that there may be modifier genes that cause the eye to make more or less melanin. Hazel eyes are one of the least understood eye colors. Researchers have a basic understanding of where brown, blue and green eyes come from genetically, but hazel eyes are a lot harder to understand and are much more complex.
Brown spots or "eye freckles" can be very common and are usually not harmful. Some recommend having them checked by an eye doctor, just to be sure.
Hazel?
A different variation of brown. Who am I?
In humans, brown eyes result from a relatively high concentration of melanin in the stroma of the iris, which causes light of both shorter and longer wavelengths to be absorbed.
Green or
Blue with Yellow?
Hazel eyes are common throughout caucasion populations, in particular in regions where blue, green and brown-eyed peoples are intermixed. Hazel eyes are less common than brown eyes, but more common than green eyes. They are commonly found in many countries throughout the world, but especially in the United States and European countries. Many people with hazel eyes are of European descent. Hazel eyes are rare in Africa and Asia where brown is often the only eye color found.
Prevalence
Hazel eyes are due to a combination of Rayleigh scattering and a moderate amount of melanin in the iris' anterior border layer. This eye color can be difficult to define since there is often substantial variation in this eye color. Hazel eyes often appear to shift in color from a brown to a green. Although hazel mostly consists of brown and green, the dominant color in the eye can either be brown/gold or green. This is how many people mistake hazel eyes to be amber and vice versa.
Hazel Eyes
The genetics of eye color are complicated, and color is determined by multiple genes. So far, as many as 15 genes have been associated with eye color inheritance.

The once-held view that blue eye color is a simple recessive trait has been shown to be incorrect. Sometimes blue seems to be recessive, but not always. The genetics of eye color are so complex that almost any parent-child combination of eye colors can occur.
The Basics of Eye Color
Factor #1: The pigmentation of the iris

This varies from light brown to black, depending on the concentration of melanin in the iris pigment epithelium (located on the back of the iris), the melanin content within the iris stroma (located at the front of the iris), and the cellular density of the stroma.
Eye color is determined by two distinct factors...
Most babies who have European ancestry have light-colored eyes before the age of one. As the child develops, melanocytes (cells found within the iris of human eyes, as well as skin and hair follicles) slowly begin to produce melanin. Because melanocyte cells continually produce pigment, in theory eye color can be changed. Most eye changes happen when the infant is around one year old, although it can happen up to three years of age.
Changes (lightening or darkening) of eye colors during early childhood, puberty, pregnancy, and sometimes after serious trauma do represent cause for plausible argument to state that some eyes can or do change, based on chemical reactions and hormonal changes within the body. Eye color does not change suddenly, however. People who feel their eye color changes suddenly are probably noticing their eyes reflecting colors around them, such as their shirt color, or they may appear different because of a change in lighting.
Eye colors, especially blue and green, can be strongly associated with other traits, such as freckling, mole count, hair, and skin tone.
Associations
Hetero = different
chrom = colored

Heterochromia
Because eye color can be anywhere from extremely light blue to very dark brown, eye-color classification can be difficult and individuals can fall within more than one category.

Can you classify this eye? . . . .
Easy to Classify?
Can Eye Color Change?
On the left this eye has green with brown, like hazel, but the brown forms a ring around the pupil and has blue on only one side.
What category?
Mrs. Carlsen's eye
Josie's eyes appear green, but a closer look shows she has yellow intermixed with blue.
Factor #2: Rayleigh Scattering

The appearance of blue and green, as well as hazel eyes, results from the Rayleigh scattering of light in the stroma, a phenomenon similar to that which accounts for the blueness of the sky. Neither blue nor green pigments are ever present in the human iris or ocular fluid. Eye color is thus an instance of structural color and varies depending on the lighting conditions, especially for lighter-colored eyes.
Ethan
Another photo with different lighting...
3 Types of Heterochromia:
- Complete Heterochromia
- Sectoral Heterochromia
- Central Heterochromia
Heterochromia is a somewhat rare condition where part or all of the iris is a different color from the rest of the iris or from the other eye.
Complete Heterochromia
Ethan
Sectoral Heterochromia
Ethan
Central Heterochromia
Ethan
One iris is completely different from the other
where a part of the iris is a different color from the remainder of the same iris
Whose eye in seventh grade possibly has sectoral heterochromia?
Preston
(this photo is from the internet)
An eye condition where there are two colors in the same iris; the area around the pupil is a different color than the outer area, with the true iris color being the outer color.
Whose am I?
Bobby's
Emma's eyes could be confused as
amber, but true amber eyes do not
contain the variations Emma's have.
Emma L.'s
Prevalence
Emma Shoo.'s
Eyes can have so much melanin in them that they appear almost black.








Can you guess whose
this is?
Can you guess this pretty, brown eye?
Olivia's
Katherine
Rives
Preston
This person's other eye with different lighting
What about
this gem?
Josie's eyes appear green, but a closer look shows she has yellow intermixed with blue.
Another
variation of blue...
This eye has
very little melanin.
Whose baby blue is this?
Liz's
(again, blue with
yellow striations)
Some eyes have a dark ring around
the iris, called a limbal ring.
William M.
Parker's
Matthew's
Whose hazel eye is this?
Isabel
Emma Love's
Brown eyes are very common, but they shouldn't be overlooked for their beauty because of their prevalence.
Emma's eyes could be confused as
amber, but true amber eyes do not
contain the variations Emma's have.
Annika
In humans, yellowish specks or patches are thought to be due to the pigment lipofuscin, also known as lipochrome.
Ethan
Other common eye colors include grey and amber.

Elizabeth Taylor (an actress) was said to have eyes that photographed purple, but they usually appeared blue.
Whose am I?
Bobby's
Rives
People with albinism have little or no pigment in their eyes, skin, or hair. They have inherited altered genes that do not make the usual amounts of melanin. Some people with albinism have reddish eyes, violet eyes, or blue eyes. Occasionally they have have hazel or brown eyes.
Rives
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