Let me tell you a little about Albinos first.
Red and violet
The eyes of people with severe forms of albinism may appear red under certain lighting conditions owing to the extremely low quantities of melanin, allowing the blood vessels to show through. (An organism or person with complete absence of melanin is called an albino an organism or human with only a diminished amount of melanin is described as albinoid.) In addition, flash photography can sometimes cause a "red-eye effect", in which the very bright light from a flash reflects off the retina, which is abundantly vascular, causing the pupil to appear red in the photograph. Although the deep blue eyes of some people such as Elizabeth Taylor can appear violet at certain times, "true" violet-colored eyes occur only due to albinism.
"The gene OCA2 that causes the pink eye color and hypopigmentation common in Albinos, is also strongly associated with blue and green eyes. . .. The appearance of blue, 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 [of all but brown eyes] thus varies depending on the lighting conditions. . . Those who have albinism in a less severe form have the lightest blue eyes with no melanin on the front of the iris at all, but they have dark brown coloration on the back of it, to prevent light from scattering around inside the eye.
Most babies who have European ancestry have light-colored eyes [at least] before the age of one. As the child develops, melanocytes . . . slowly begin to produce melanin. Most eye changes happen when the infant is around one year old, although it can happen up to three years of age. Observing the iris of an infant from the side using only transmitted light with no reflection from the back of the iris, it is possible to detect the presence or absence of low levels of melanin.
" A genetic mutation leads to blue eyes. . .Originally, we all had brown eyes."
Source
Distribution of light-eyed people in Europe.
As you can see, it seems that the gene for blue eyes had an origin and got diluted from there to the rest of Europe.
Though the people with blue eyes in America came from European descent, "the melting pot of the world", time and interbreeding has made the gene mutation less and less common with only 16.6% of the total population, and 22.3% of the white population having blue eyes.
In those with milder forms of albinism, the color of the iris is typically blue but can vary. Source
Like blue eyes, gray eyes have a relatively clear stroma.
One possible explanation for the difference in the appearance of gray and blue eyes is that gray eyes differ in the concentration of melanin at the front of the stroma. Gray eyes are also most common in Northern and Eastern Europe. . . Under magnification, gray eyes exhibit small amounts of yellow and brown color in the iris.
In a study published in Human Genetics it was shown that a mutation of the HERC2 gene, is hypothesized to interact with the OCA2 gene. . . This genetic mutation in our chromosomes resulted in the creation of a 'switch,' which literally 'turned off' the ability to produce brown eyes." The genetic switch is located in the gene adjacent to OCA2 and rather than actually completely turning off the gene, the switch merely limits its action. Reducing the production of melanin in the iris. In effect, the turned-down switch diluted brown eyes to blue. If the OCA2 gene had been completely shut down, our hair, eyes and skin would be melanin-less, a condition known as albinism.
In humans, there are two principal types of albinism, oculocutaneous, affecting the eyes, skin and hair, and ocular affecting the eyes only.
Cataracts are often an effect of eye injuries and diabetes. . . African Americans, Hispanic/Latino Americans, American Indians, and some Asian Americans and Native Hawaiians or other Pacific Islander Americans are at particularly high risk for type 2 diabetes. Basically, "minorities have a higher prevalence of type 2 diabetes than whites." (Curable by a good diet BTW)
For the majority of us, each individual hair strand has three layers. The layers (starting from the outside) are the cuticle, cortex, and medulla. Fine texture hair usually associated with Europeans, Australians, and Americans, typically only has two layers. The inside of the hair, the medulla, is often missing, so hair can be limp and look thin naturally.
Most babies who have European ancestry have light-colored eyes [at least] before the age of one. As the child develops, melanocytes . . . slowly begin to produce melanin. Most eye changes happen when the infant is around one year old, although it can happen up to three years of age. Observing the iris of an infant from the side using only transmitted light with no reflection from the back of the iris, it is possible to detect the presence or absence of low levels of melanin.
" A genetic mutation leads to blue eyes. . .Originally, we all had brown eyes."
Source
Distribution of light-eyed people in Europe.
Though the people with blue eyes in America came from European descent, "the melting pot of the world", time and interbreeding has made the gene mutation less and less common with only 16.6% of the total population, and 22.3% of the white population having blue eyes.
In those with milder forms of albinism, the color of the iris is typically blue but can vary. Source
Like blue eyes, gray eyes have a relatively clear stroma.
One possible explanation for the difference in the appearance of gray and blue eyes is that gray eyes differ in the concentration of melanin at the front of the stroma. Gray eyes are also most common in Northern and Eastern Europe. . . Under magnification, gray eyes exhibit small amounts of yellow and brown color in the iris.
-
- Green is the least common eye color and as in the case of blue and grey eyes, the color of green eyes does not result simply from the pigmentation of the iris. Rather, their 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.
- Green eyes are most common in Northern and Central Europe. They can also be found in Southern Europe. . .
Hazel
Hazel eyes are due to a combination of Rayleigh scattering and a moderate amount of melanin in the iris.
In humans, there are two principal types of albinism, oculocutaneous, affecting the eyes, skin and hair, and ocular affecting the eyes only.
Types of Albinism
While most people with albinism have very light skin and hair, not all do. Oculocutaneous (pronounced ock-you-low-kew-TAIN-ee-us) albinism (OCA) involves the eyes, hair and skin. Ocular albinism (OA), which is much less common, involves primarily the eyes, while skin and hair may appear similar or slightly lighter than that of other family members.
Over the years, researchers have used various systems for classifying oculocutaneous albinism. In general, these systems contrasted types of albinism having almost no pigmentation with types having slight pigmentation. In less pigmented types of albinism, hair and skin are cream-colored and vision is often in the range of 20/200. In types with slight pigmentation, hair appears more yellow or red-tinged and vision may be better. [I.e, the less albinisim the better the eyes are.]
Recent research has used analysis of DNA, the chemical that encodes genetic information, to arrive at a more precise classification system for albinism. Four forms of OCA are now recognized – OCA1, OCA2, OCA3 and OCA4; some are further divided into subtypes.
- Oculocutaneous albinism type 1 (OCA1 or tyrosinase-related albinism) results from a genetic defect in an enzyme called tyrosinase (hence ‘ty’ above). This enzyme helps the body to change the amino acid tyrosine into pigment. (An amino acid is a “building block” of protein.) There are two subtypes of OCA1. In OCA1A, the enzyme is inactive and no melanin is produced, leading to white hair and very light skin. In OCA1B, the enzyme is minimally active and a small amount of melanin is produced, leading to hair that may darken to blond, yellow/orange or even light brown, as well as slightly more pigment in the skin.
- Oculocutaneous albinism type 2 (OCA2 or P gene albinism) results from a genetic defect in the P protein that helps the tyrosinase enzyme to function. Individuals with OCA2 make a minimal amount of melanin pigment and can have hair color ranging from very light blond to brown.
- Oculocutaneous albinism type 3 (OCA3) is rarely described and results from a genetic defect in TYRP1, a protein related to tyrosinase. Individuals with OCA3 can have substantial pigment.
- Oculocutaneous albinism type 4 (OCA4) results from a genetic defect in the SLC45A2 protein that helps the tyrosinase enzyme to function. Individuals with OCA4 make a minimal amount of melanin pigment similar to persons with OCA2.
Something that is common to albinos are eye issues, resulting from abnormal development of the eye because of lack of pigment. These include one or more of these:
- legal blindness
- age related macular degeneration
- increased risk of uveal melanoma
- horizontal back and forth movement of the eyes
- muscle imbalance of the eyes, “crossed eyes” or “lazy eye”.
- sensitivity to bright light and glare
- far-sighted or near-sighted
- have a stigmatism
- the retina does not develop normally before birth and in infancy
- Optic nerve misrouting: the nerve signals from the retina to the brain do not follow the usual nerve routes
The leading cause of blindness among white persons was age-related macular degeneration (54.4% of the cases), while among black persons, cataract and glaucoma accounted for more than 60%of blindness.
Cataracts are often an effect of eye injuries and diabetes. . . African Americans, Hispanic/Latino Americans, American Indians, and some Asian Americans and Native Hawaiians or other Pacific Islander Americans are at particularly high risk for type 2 diabetes. Basically, "minorities have a higher prevalence of type 2 diabetes than whites." (Curable by a good diet BTW)
Some of the causes of glaucoma (that lead to most of the rest of the eye problems in minorities) include: an injury to the eye, severe eye infection, inflammatory conditions of the eye, and occasionally eye surgery to correct another condition. (Like cataracts.)
Considering the high rate of minorities with type 2 diabetes, and also the high rate of minorities in sports or rough jobs, as well as in gangs, it seems likely that the vast majority of eye problems of minorities in the USA are lifestyle induced, as opposed to the genetic issues facing the person with light eyes.
Well, we can see the fascinating difference in the eyes of the albino. . . leading me to say that an albinoid is basically a person with light eyes. . . but what about their hair? What does a person with very low levels of melanin in their hair look like? Here's what I learned:
"Hair color is the pigmentation of hair follicles due to two types of melanin: Phaeomelanin, and Eumelanin. Eumelanin is the dark pigment which is predominate in black hair. Phaeomelanin is a lighter pigment, which is found in red and blond hair. Many people's hair contains a mixture of the two: the more eumelanin there is in the mixture, the darker is the hair.
Blond hair can have almost any proportion of pheomelanin and eumelanin . . . More pheomelanin creates a more golden blond color, and more eumelanin creates an ash blond.
Natural blond hair is rare in adulthood, with some reports that only about 2% of the world's population is naturally blond. Blond hair is most commonly found in Northern and Eastern Europeans and their descendants [in America], but can be found spread around most of Europe.
Blond hair is exceptionally rare among those without European heritage. . . Sub-saharan African has the lowest [rate of blond hair]. . .
Auburn hair
The chemicals which cause auburn hair are eumelanin (brown) and pheomelanin (red), with a higher proportion of red-causing pheomelanin than what is found in average brown hair. It is most commonly found in individuals of Northern and Western European descent.
Chestnut hair
Chestnut hair is a hair color which is a reddish shade of brown hair. In contrast to auburn hair, the reddish shade of chestnut is darker. Chestnut hair is common among the native peoples of Northern, Central, Western, and Eastern Europe.Red hair
Red hair ranges from light strawberry blond shades to titian, copper and less commonly "true" red. It is caused by a variation in the Mc1r gene and is recessive. Red hair has the highest amounts of pheomelanin, around 67%, and usually low levels of eumelanin. At 1-2% of the population, it is the least common hair color in the world. . .For the majority of us, each individual hair strand has three layers. The layers (starting from the outside) are the cuticle, cortex, and medulla. Fine texture hair usually associated with Europeans, Australians, and Americans, typically only has two layers. The inside of the hair, the medulla, is often missing, so hair can be limp and look thin naturally.
Medium texture hair is thinner than coarse hair but not as thin as fine hair. Medium is in between the two. Medium is also the most common type of hair texture.
Hair that is very thick or wiry in texture is referred to as coarse hair. Coarse hair is strong and may be ultra straight or ultra curly.
Now let's talk about what that Melanin (or lack of it) does to the skin: Melanin in the skin controls the amount of ultraviolet (UV) radiation from the sun that penetrates by absorption. UV radiation can then assist in the production of vitamin D.
There are two types of melanin. The most common form of biological melanin is eumelanin. Eumelanin is found in hair, areola, and skin, and the hair colors grey, black, yellow, and brown. In humans, it is more abundant in people with dark skin.
between the albino skin, hair, and eyes, and the black skin,
hair and eyes, are these:
SLC24A5
"Solute carrier family 24 member 5 (SLC24A5) regulates calcium in melanocytes and is important in the process of melanogenesis. TheThr111Ala allele (rs1426654) has been shown to be a major factor in the light skin tone of Europeans in a number of studies. The Ala111Thr or rs1426654 polymorphism in the coding region of the SLC24A5 gene is frequent in and mainly restricted to populations in Europe, North Africa, the Horn of Africa, West Asia, Central Asia and South Asia. It is believed to represent some 25–40% of the difference in skin tone between Europeans and Sub-Saharan Africans, and appears to have arisen as recently as within the last 10,000 years.
[edit]SLC45A2
Solute carrier family 45 member 2 (SLC45A2 or MATP) aids in the transport and processing of tyrosine, a precursor to melanin. It has also been shown to be a major factor in the skin color of modern Europeans through its Phe374Leu (rs16891982) variation. Like SLC24A5 it is ubiquitous in European populations but extremely rare elsewhere.
[edit]TYR
The TYR gene encodes the enzyme tyrosinase, which is involved in the production of melanin from tyrosine. It has an allele, Ser192Tyr(rs1042602), found solely in 40–50% of Europeans and linked to light-colored skin in studies of mixed-race South Asian] and African-American populations.
[edit]OCA2
Oculocutaneous albinism II (OCA2) assists in the regulation of pH in melanocytes. The His615Arg (rs1800414) allele has been shown to account for about 8% of the skin tone difference between African and East Asian populations. It is found in 85% of East Asian samples and is non-existent in European and African samples.
MC1R
The gene MC1R is primarily responsible for determining whether pheomelanin and eumelanin are produced in humans. Mutations of this very polymorphic gene have been shown to cause red hair and pale skin that does not tan in a small percentage of the human population. Although these alleles have differing frequencies across African, European and Asian populations, there is no evidence of positive selection for them and they do not appear to be associated with the evolution of lighter skin in Eurasian populations."
Source
"Dark skin with large concentrations of melanin protects against exposure to ultraviolet light and skin cancers; and light-skinned people have about a tenfold greater risk of skin cancer, compared with dark-skinned persons, under equal sunlight exposure. Excessive solar radiation causes direct and indirect DNA damage to the skin. It would have, on the other hand, represented a health benefit to have light skin in reduced sunlight, [Like humans living in caves, or underground or where the light source was further away. . .] as it maximizes the synthesis of vitamin D."
The leading hypothesis for the evolution of human skin color proposes that:
Source
"Dark skin with large concentrations of melanin protects against exposure to ultraviolet light and skin cancers; and light-skinned people have about a tenfold greater risk of skin cancer, compared with dark-skinned persons, under equal sunlight exposure. Excessive solar radiation causes direct and indirect DNA damage to the skin. It would have, on the other hand, represented a health benefit to have light skin in reduced sunlight, [Like humans living in caves, or underground or where the light source was further away. . .] as it maximizes the synthesis of vitamin D."
The leading hypothesis for the evolution of human skin color proposes that:
- From ~1.2 million years ago to 10,000 years ago, the ancestors of all people alive were dark-skinned Africans.
- As populations began to migrate out of Africa, sometime around 10,000 years ago, the evolutionary constraint keeping skin dark dark, proportionally to the distance North a population migrated, resulting in a range of skin tones within northern populations.
- At some point, northern populations experienced positive selection for lighter skin due (presumably) to the increased production of vitamin D from sunlight and the genes for darker skin disappeared from these populations.
A number of researchers disagree with this and suggest that the northern latitudes permitted enough synthesis of vitamin D [for even a black person] combined with food sources from hunting to keep populations healthy, and only when agriculture was adopted was there a need for lighter skin to maximize the synthesis of vitamin D. . .This theory is supported by a study into the SLC24A5 gene which found that the allelle associated with light skin in Europe may have originated as recently as 6,000–10,000 years ago which is in line with the earliest evidence of farming."
Source
"Scientists conclude that the mutation [that leads to the light skin, as well as the blue eyes and the red and blond hair] may have arisen in a single [or a few] individual(s), probably living in the northwestern part of the Black Sea region [of Europe] . . . 6,000–10,000 years ago during the Neolithic revolution." [the transition of human culture from a lifestyle of animal like hunting and gathering to one of agriculture and settlement.]
Source
Source
"Scientists conclude that the mutation [that leads to the light skin, as well as the blue eyes and the red and blond hair] may have arisen in a single [or a few] individual(s), probably living in the northwestern part of the Black Sea region [of Europe] . . . 6,000–10,000 years ago during the Neolithic revolution." [the transition of human culture from a lifestyle of animal like hunting and gathering to one of agriculture and settlement.]
Source
No comments:
Post a Comment