Brown Eyes Blue Eyes Case Study

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White Privilege - Brown Eye Blue Eye Experiment - part 1

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According to World Atlas , those with brown eyes make up anywhere from 55 to 79 percent of the world's population, whereas those with green eyes make up just two percent of the global population. Two percent! Coming in rarer than green is gray — and that means true gray, not blue that sometimes looks gray — red or violet, and heterochromia meaning two different colored eyes. As Medical Daily reported, the majority of redheads have one of the three eye colors: brown, hazel, or green. Okay, we know we just told you that green eyes are incredibly rare. And they are. However, if you were to take a trip to Europe, you'd probably start to doubt this fact. Edmund Custers, a biostatistician, revealed in an article for Owlcation that a whopping 86 percent of the population in Ireland and Scotland have either blue or green eyes.

The situation is similar in Iceland, as 87 percent of men and 89 percent of women have one of the two colors. The expert further explained, "Among European Americans, green eyes are most common in people of recent Celtic or Germanic ancestry. In fact, if you were to visit Britain, you might start to believe that green eyes are more prevalent than brown. According to a study of over 12, people conducted by ScotlandsDNA via The Herald , brown eyes are rarer than green in Britain, despite the fact that brown eyes make up much of the world's population. Although we may label people's eyes as "green," no one actually has green eyes. That is, irises only appear to be that color.

According to Eyesite. Instead, they're a "curious blend of light brown pigmentation, a yellowish lipochrome pigment, and a splash of Rayleigh scattering. In an article for Owlcation , biostatistician Edmund Custers broke down this strange phenomenon. Basically, "green" eyes only contain a small amount of the brown pigment called melanin. In the absence of a lot of melanin, Rayleigh scattering happens. Rayleigh scattering is when, as Custers explained, "longer wavelengths of light pass straight through the eye, then they are absorbed at the back of the eye. Although Rayleigh scattering is also responsible for making blue eyes, well, blue, green eyes are especially unique because of this "curious blend" of blue wavelengths and yellowish pigment.

You may not know if your child has green eyes until quite a while after giving birth. When first born, a baby has one of two eye colors: gray or blue. That said, immediately after birth, cells called melanocytes begin to secrete melanin, the brown pigment, in the baby's irises, explains Healthychild. This starts happening because melanocytes react to light and, um, you know, there aren't exactly any sunny days in the womb. However, this process isn't like glow-in-the-dark technology. You can't just take your baby into the sunshine and expect to see their true eye color after stepping back inside.

Melanocytes can take up to a year to finish producing pigment. That said, you should begin to have an idea of your child's eye color at around the six-month mark because the process starts wrapping up at around this time. If, after a year, your child has green peepers, you can be confident that they're there to stay. Instead of waiting a whole year to find out if your child is going to have green eyes, you might think it easier to comb through your family history for any prevalence of this eye color. However, it's not quite as simple as just tracking down eye colors. The Tech Museum of Innovation explained that there are many genes — and eye colors — at play.

Today, scientists believe there are at least eight — and, more than likely, as many as 16 — genes involved in determining a person's final eye color. So, yeah, it might actually be easier if you just wait until your child's first birthday to figure out their eye color. Although the science isn't exactly clear on why women are more likely to have green eyes, we just know that this seems to be the case. Froelich and W. Robert Stephenson of Iowa State University found that nearly 12 percent of male participants surveyed reported having green eyes, while nearly 18 percent of the female participants had green. Although the researchers noted that more data should be collected on the subject, these results are similar to other studies.

The Daily Beast reported that the National Longitudinal Survey of Youth reported that more women than men had green eyes. Eye color is an inherited trait influenced by more than one gene. These changes are known as single-nucleotide polymorphisms or SNPs. The actual number of genes that contribute to eye color is currently unknown, but there are a few likely candidates. The name of the gene is derived from the disorder it causes, oculocutaneous albinism type II. Different SNPs within OCA2 are strongly associated with blue and green eyes as well as variations in freckling , mole counts, hair and skin tone. The polymorphisms may be in an OCA2 regulatory sequence , where they may influence the expression of the gene product, which in turn affects pigmentation. Blue eyes with a brown spot, green eyes, and gray eyes are caused by an entirely different part of the genome.

People of European descent show the greatest variety in eye color of any population worldwide. Recent advances in ancient DNA technology have revealed some of the history of eye color in Europe. All European Mesolithic hunter-gatherer remains so far investigated have shown genetic markers for light-colored eyes, in the case of western and central European hunter-gatherers combined with dark skin color. Iris color can provide a large amount of information about a person, and a classification of colors may be useful in documenting pathological changes or determining how a person may respond to ocular pharmaceuticals. Normal eye colors range from the darkest shades of brown to the lightest tints of blue.

Green irises, for example, have some yellow and the blue structural color. Brown irises contain more or less melanin. Some eyes have a dark ring around the iris, called a limbal ring. Eye color in non-human animals is regulated differently. For example, instead of blue as in humans, autosomal recessive eye color in the skink species Corucia zebrata is black, and the autosomal dominant color is yellow-green. As the perception of color depends on viewing conditions e. Most newborn babies who have European ancestry have light-colored eyes. 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. Adult eye color is usually established between 3 and 6 months of age, though this can be later. An iris that appears blue under this method of observation is more likely to remain blue as the infant ages. An iris that appears golden contains some melanin even at this early age and is likely to turn from blue to green or brown as the infant ages. Changes lightening or darkening of eye colors during early childhood, puberty, pregnancy, and sometimes after serious trauma like heterochromia do represent cause for a plausible argument stating that some eyes can or do change, based on chemical reactions and hormonal changes within the body.

Studies on Caucasian twins, both fraternal and identical, have shown that eye color over time can be subject to change, and major demelanization of the iris may also be genetically determined. Most eye-color changes have been observed or reported in the Caucasian population with hazel and amber eyes. The higher the amount of these pigments in the Iris and the denser their texture, the darker the color of a person's eyes; The same melanin concentration also depends on many factors such as hereditary, environmental, and other factors. The most important role of eye melanins is to protect the eyes from the sun's harmful rays. Therefore, they should protect their eyes from the sun more than other people.

The human eye consists of two types of light and color receptors in the Retina. Cylindrical cells are the photoreceptors of the eye that have a black and white vision and, depending on the amount of light received from the environment, determine the amount of darkness and brightness of objects. The number of cylindrical cells is more than the number of color receptors and reaches about million; Cone cells, which are smaller in number than light receptors, have color vision and are divided into three distinct categories, each of which recognizes one of the colors blue, red, and green, allowing the individual to distinguish colors.

When a person is exposed to sunlight, the rays of sunlight hit a part of the back of the eye called the Yellow spot. The cylindrical cells receive these rays, make a neural message from them, and send them to the occipital region of the brain, where they are examined and answered if necessary. At this time, a large amount of ultraviolet light is received by the eye and destroys parts of the light receptors.

This difference in the number of light receptors in the eyes of different people causes a difference in the amount of light they receive from the environment; For this reason, people with bright eyes see colors a little darker than others; But this amount is so small that it is not very visible in everyday life and only appears as a slight difference of opinion between people with different eye colors. Carleton Coon created a chart by the original Martin scale. The numbering is reversed on the scale below in the later Martin—Schultz scale , which is still used in physical anthropology. This may be due to the deposition of the yellow pigment called lipochrome in the iris which is also found in green eyes. Also, hazel eyes may appear to shift in color and consist of flecks and ripples, while amber eyes are of a solid gold hue.

Amber eyes may also contain amounts of very light gold-ish gray. The eyes of some pigeons contain yellow fluorescing pigments known as pteridines. It is possible to find people with that eye color in the Balkan region , as well as in Hungary , in Southern France , Italy , and to a lesser degree in the Iberian Peninsula , Southern Cone and Middle East. 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. Longer wavelengths of light tend to be absorbed by the dark underlying epithelium, while shorter wavelengths are reflected and undergo Rayleigh scattering in the turbid medium of the stroma. In humans, the inheritance pattern followed by blue eyes is considered similar to that of a recessive trait in general, eye color inheritance is considered a polygenic trait , meaning that it is controlled by the interactions of several genes, not just one.

Blue eyes are common in northern and eastern Europe, particularly around the Baltic Sea. A Birman kitten with distinctive sapphire blue eyes. The first blue-eyed koala known to be born in captivity [46]. The same DNA sequence in the region of the OCA2 gene among blue-eyed people suggests they may have a single common ancestor. As of [update] , the earliest remains of Homo sapiens with genes for both light-pigmentation and blue-eyes were found in 7, years old Mesolithic hunter-gatherers from Motala , Sweden. Blue eyes are continuing to become less common among American children. Blue eyes are rare in mammals; one example is the recently discovered marsupial, the blue-eyed spotted cuscus Spilocuscus wilsoni.

The trait is hitherto known only from a single primate other than humans — Sclater's lemur Eulemur flavifrons of Madagascar. While some cats and dogs have blue eyes, this is usually due to another mutation that is associated with deafness. But in cats alone, there are four identified gene mutations that produce blue eyes, some of which are associated with congenital neurological disorders. The mutation found in the Siamese cats is associated with strabismus crossed eyes.

The mutation found in blue-eyed solid white cats where the coat color is caused by the gene for "epistatic white" is linked with deafness. However, there are phenotypically identical, but genotypically different, blue-eyed white cats where the coat color is caused by the gene for white spotting where the coat color is not strongly associated with deafness. In the blue-eyed Ojos Azules breed, there may be other neurological defects. Blue-eyed non-white cats of unknown genotype also occur at random in the cat population. 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.

Dark brown eyes are dominant in humans [57] and in many parts of the world, it is nearly the only iris color present. Like blue eyes, gray eyes have a dark epithelium at the back of the iris and a relatively clear stroma at the front. One possible explanation for the difference in the appearance of gray and blue eyes is that gray eyes have larger deposits of collagen in the stroma, so that the light that is reflected from the epithelium undergoes Mie scattering which is not strongly frequency-dependent rather than Rayleigh scattering in which shorter wavelengths of light are scattered more.

This would be analogous to the change in the color of the sky, from the blue given by the Rayleigh scattering of sunlight by small gas molecules when the sky is clear, to the gray caused by Mie scattering of large water droplets when the sky is cloudy. As with blue eyes, the color of green eyes does not result simply from the pigmentation of the iris. The green color is caused by the combination of: 1 an amber or light brown pigmentation in the stroma of the iris which has a low or moderate concentration of melanin with: 2 a blue shade created by the Rayleigh scattering of reflected light.

Green eyes probably result from the interaction of multiple variants within the OCA2 and other genes. They were present in south Siberia during the Bronze Age. They are most common in Northern , Western and Central Europe. Green eyes are common in tabby cats as well as the Chinchilla Longhair and its short-haired equivalents; they are notable for their black-rimmed sea-green eyes. Hazel eyes are due to a combination of Rayleigh scattering and a moderate amount of melanin in the iris' anterior border layer. This is how many people mistake hazel eyes to be amber and vice versa. The two most common species of albino birds are the common house martin and the American robin.

In one study, albinism in birds has been categorised according to the extent of pigment absence. However, it has been argued that the definition of albinism precludes the possibility of "partial albinism" in which a mostly white bird shows some form of melanin pigmentation. As with other animals, it has been stated that for fish to be properly described as "albino", they must have a white body and pink or red eyes.

Several types of aquarium fish have "albino" in their names, e. Zebrafish have three types of chromatophores—iridophores, melanophores, and xanthophores—which produce silver, black, and yellow pigmentation respectively. Zebrafish that lack iridophores are known as roy mutants , those that lack melanophores as albino mutants , and those which lack both melanophores and iridophores are ruby mutants. The gross eye morphology, feeding and swimming behaviours between wild-type and albino zebrafish were indistinguishable, except under dim or bright light or low contrast. However, when tested, there was no differences in responses between wild-type and albinistic European wels catfish Silurus glanis and South American bronze catfish Corydoras aeneus.

Similarly, Mexican blind cave fish Astyanax mexicanus do not differ in hearing sensitivity from the normally pigmented and eyed surface-dwelling populations. Fish lack melanin in the inner ear, meaning that hearing in fishes is less likely to be affected by albinism than in mammals. There are several reports of total albinism in both freshwater and marine fish, however, frequently captured albino fish are only reported in aquarium magazines and local newspapers.

The incidence of albinism can be artificially increased in fish by exposing the eggs to heavy metals e. In the wild, albinism is reasonably common in the teleosts , especially the Pleuronectiformes flatfish , however, it is rarely reported in the elasmobranchs. Albino and normally pigmented channel catfish Ictalurus punctatus differ in their characteristics. Normal individuals of this species are superior to albinos in body weight and total length.

Albinos crossed with other albinos require 11 days longer to spawn and produce smaller egg masses. These masses contain eggs of lighter weight with poorer hatchability than crosses of normal fish. The albino fish have lower survival rates than normal fish but dress-out percentages are nearly equal. Some wild cave fish have populations that are albinistic. The Mexican cave tetra is a species that has evolved specialized characteristics in a series of independent caves.

One of these is albinism linked to the Oca2 gene, a known pigmentation gene, This trait has evolved independently in at least two caves. In the class Chondrichthyes , several species of naturally occurring albino rays and sharks have been recorded. Furthermore, an albino individual spotted ratfish Hydrolagus colliei from the order Chimaeriformes has been reported. Albinistic individuals of the following shark species have been reported: [48] [49] [50]. A study published in reported albinistic individuals of the following ray species: [49]. There are several reports of albino lampreys and it has been estimated that this occurs at a frequency of one in , normal individuals.

Albinism in the African lungfish has been reported on at least two occasions. Many reptiles labeled as albino are, in fact, not completely lacking in all colour pigments. They are actually amelanistic , not albino. Reptiles often possess at least two pigments. Among the most common are xanthin yellow and erythrin red. An amelanistic reptile therefore, may still have pale yellow, orange, or red pigmentation. The California Academy of Science , in the Steinhart Aquarium , as of , has on display an albino American alligator named " Claude ". The alligator is partially blind because of lack of pigment in its eyes. This alligator would not have survived in the wild because its whiteness would have made it too easy a prey object.

The only known albino alligators are in captivity. However, most of these animals are leucistic given that they have a general loss of pigmentation with some colour tinges remaining on their bodies although looking at first like other albino creatures, thus creating the misconception that the reptiles are albino themselves when they are not. Four such alligators are kept at the Gatorland theme park in the U. In snakes, partial absence of pigment is more common than absolute albinism. For snakes that are usually patterned in colours, they appear as a faint blue, peach or yellowish.

In these cases, there has been a genetic mutation in the melanin and pigment delivery. The appearance comes from the inability for full colours to be present, such as black, red, brown and others. The eyes of an albino snake are typically red or pink. Albino snakes can remain in the sunlight for several hours with minimal harm. Corn snakes and snakes of larger types, such as a boa or diamondback snakes, are the most commonly affected by albinism often appearing to be a pinkish or yellowish colour. Albino tortoises and turtles are uncommon; Sulcata tortoises are the most likely type of turtle to express albinism.

The shells have an almost yellow colouration and they have pink eyes. For turtles, a pure white colour is nearly impossible, even with albinism. Albino turtles can have a longer lifespan than many other albino animals; their hard shells help to prevent predation and other environmental challenges. Vision and sensory organs are slightly affected. An albino anole has been reported and photographed. There are three known "albino" strains of leopard gecko , however, breeders state that albinos are generally recognized by their lack of black pigment and having red eyes is not a requirement to be considered an albino.

These three strains are called "tremper albinos", "rainwater albinos" and "bell albinos". As with reptiles, many amphibians labeled as albino are, in fact, not completely lacking in all colour pigments. They are actually amelanistic, not albino. Amphibians have six types of chromatophore in their skin, i. The incidence of albinism in frogs, salamanders, and newts is relatively higher than other taxa. It has been estimated that one in four hundred of these animals is albino.

When albino tadpoles hatch, they are almost transparent. This may help camouflage them initially, however, after two weeks, when their hindlegs begin to emerge, they become milky white. A survey in found hundreds of tiny albino plains leopard frogs , but when the researcher returned a few months later, not a single albino adult could be found. In European Salamandridae , albinism has been recorded in the fire salamander Salamandra salamandra , gold-striped salamander Chioglossa lusitanica , Italian crested newt Triturus carnifex , marbled newt Triturus marmoratus , Iberian ribbed newt Pleurodeles waltl , alpine newt Ichthyosaura alpestris and two sub-species of the smooth newt Lissotriton vulgaris vulgaris and Lissotriton vulgaris meridionalis.

Albinism in molluscs has been recognized to be a hereditary phenomenon at least since Sometimes an individual snail has a normally pigmented body, but the shell is completely without the normal pigmentation because of a defect in the cells of the mantle. Shells of certain mollusc species can be translucent when they lack the normal pigmentation. An exhibit showing albino and normal specimens of nine local species of marine molluscs, both gastropods and bivalves The Bailey-Matthews National Shell Museum in Sanibel, Florida. Normal left and albinistic right forms of the land snail Pseudofusulus varians , note that in the albino both the body and the shell are lacking the normal pigmentation.

Albino freshwater snail Biomphalaria glabrata showing the red oxygen-transport pigment haemoglobin. Without its normal pigment, the shell of this species is translucent. The neurohormone [His7]-corazonin induces darkening of the cuticle of Locusta migratoria. The Okinawa strain of this species is deficient in [His7]-corazonin and is albino. One of the typical features of Locusta migratoria is that they are gregarious locusts. However, the albino strain shows more solitarious behaviour. The yellow mutation in fruit flies is a mutation causing a congenital lack of normal pigment; it is a similar phenomenon to albinism in other organisms. The Japanese sea cucumber Apostichopus japonicus is an echinoderm that is caught in the wild or cultivated for food.

Normal Japanese sea cucumbers start to develop pigmentation when they are about 1 cm long. The upperside becomes a dull, yellowish -brown to maroon and the underside a light brown. The body walls of adult, albino Japanese sea cucumbers contain only 0. The difference in melanin content becomes visually apparent at 60 days of age. The epidermis is thinner in the albinos and contains fewer melanocytes.

Albino individuals are similar to normal individuals in growth rate, digestion rate and fertility. Astaxanthin is the main carotenoid in marine crustaceans and fish. It has been shown that adding astaxanthin to the feed can improve the skin and muscle colour of marine organisms and thereby increase their commercial and ornamental value. This albinism does not affect mortality. In some animals, albinism-like conditions may affect other pigments or pigment-production mechanisms:. Plants that are pale simply from being in the dark are termed etiolated. Albino redwoods are rare examples of an albino tree with white needles; despite its lack of chlorophyll it may grow to substantial size as a parasite , usually on the base of the normal redwood tree from which it first grew.

Albinism has frequently occurred in progeny of Black Tartarian , Bing and Hedelfingen varieties of sweet cherry. Members of the society at the University of North Texas petitioned for an election to name their albino squirrel as the university's secondary mascot. The University of Louisville in Kentucky also has a documented population of albino squirrels. Albino animals are often kept as pets, for example, African clawed frog , guinea pigs and peacocks. From Wikipedia, the free encyclopedia. This article is about the biological term. For the medical condition in humans, see Albinism in humans. For other uses, see Albino disambiguation. Examples of albino laboratory mammals. Mice with Type I oculocutaneous albinism.

Rat with Type I oculocutaneous albinism. Main article: Animal coloration. Examples of pet mammals artificially selected for albinism. Examples of fish artificially selected for albinism. Animals portal. Albinism in humans Albinism in chickens Albino and white squirrels Dyschromia Erythrism , unusually red pigmentation Isabellinism Leukoderma Mongolian spot Xanthochromism , unusually yellow pigmentation and lack of yellow pigment. The Free Dictionary. Retrieved January 31, The Georgia Aquarium. Archived from the original on January 20, Retrieved January 20, National Organization for Albinism and Hypopigmentation.