What does human skin color depend on? melanin pigment. On human adaptation to geoclimatic factors. Why do different nations have different skin colors? Where is the gene for skin color located?
Skin color is one of the most variable characteristics in humans as a species. It is believed that it has an adaptive character, that is, it adapts to environmental conditions in order to get the maximum benefit for the body. Thus, the dark color of the skin allows you to protect it from the negative effects of excessive ultraviolet radiation in regions with a hot climate, and light skin provides increased synthesisDin areas with little sunlight.
Meanwhile, so far only a few genes associated with skin color have been known, all of which have been identified as a result of studies on the genetic material of Europeans. The authors of the new study focused on Africa, not only because this continent is considered the cradle of mankind, but also because the palette of skin tones of the inhabitants of this region is the most diverse - from light brown to almost black.
Comparison of the genetic information of almost 1,600 people from ethnically different populations and data on their skin pigmentation revealed six regions of the genome, mutations in which determine differences in skin tones. Thanks to this, scientists have been able to find answers to some of the mysteries of human evolution. For example, it became clear why East Africans have lighter skin than other Africans.
Most of the newly discovered genetic variants are very ancient. Mutations associated with dark and light skin color appeared more than 300 thousand, and some about a million years ago, even before the existence of modern man. At the same time, the oldest genetic variations determine precisely the light shade of the skin. This suggests that our ancestors were light-skinned rather than dark-skinned, said study lead author Sarah Tishkoff (Sarah Tishkoff) from Pennsylvania State University (USA).
As they lost their hairline and moved out of the jungle into the savannah, the first people needed darker skin. Tishkoff and her colleagues were able to identify traces of these genetic changes - part of the newly discovered variants that determine skin tone is associated with a reaction to ultraviolet radiation and the risk of melanoma ().
In particular, we are talking about a variant of the geneDDB 1, associated with dark skin color and responsible for the restoration of DNA in skin cells after sun exposure. Africans are comparatively rarely sick. At the same time, the "protective" variant of this gene most often found in residents of regions with the strongest ultraviolet radiation. According to Tishkoff, it is this mutation that plays a key role in the low level of skin disease in African countries. At the same time, outside of Africa, this mutation is not supported by natural selection; it practically does not occur in people with fair skin. This "switch" occurred between 60,000 and 80,000 years ago, around the time that modern humans began migrating from the African continent.
Genetic mutations sometimes change people so much that it's amazing. And it is not clear whether nature cheated them, or punished them. But they look really unique.
People with genetic abnormalities are not to blame for looking that way. Their occurrence does not depend on the will of man. Therefore, it is necessary to treat their owners with understanding and tact.
Vitiligo
This mutation results in skin, hair, and sometimes even nail color changes. There is no cure for her.
Winnie Harlow, who has vitiligo, works as a model. She is known for white stripes on the skin of the Negroid type.
Dissimilar twins
These babies developed from the same egg, but were born with different appearances, contrary to the standard stereotype that monozygotic twins should be like two peas in a pod.
piebald skin
A person with this mutation is born with completely white, devoid of melanocyte patches on the skin. And also white, similar to gray, strands of hair.
Albinism
Albinism affects people of all ethnic groups. People with this mutation are characterized by a congenital absence of the pigment melanin, which gives color to the skin, hair, and iris.
This girl is African-American, but because of an anomaly, she looks like an ordinary blonde from Europe, only with curls.
Waardenburg syndrome
People with this mutation have a gray streak above the forehead, congenital hearing loss, telecanthus, and iris heterochromia. This mother and son is only the last. That's why they have such amazing eye color.
distichiasis
With this developmental anomaly, an additional row of eyelashes appears on the upper eyelid. And the eyelashes on the bottom become thicker.
heterochromia
This girl does not have the same color of the iris of the right and left eyes. Her gaze is frightening and mesmerizing at the same time.
Gigantism
Silva Cruz is the tallest girl in the world. And the reason for this is the open epiphyseal growth zone, which occurs in people with gigantism.
split chin
Some people think that a curly chin indicates a strong-willed character. But in fact - about gene mutation. This girl does not have a gene in her body that helps the bones of the chin grow together.
Found a gene that is probably responsible for the color of human skin
A group of geneticists from the University of Pennsylvania, studying aquarium zebra fish (Zebra-fish), discovered that, most likely, plays a decisive role in the formation of skin color in humans.
Human skin color depends on the amount and size melanosome - small pigment granules in special melanocyte cells, as well as the color of the pigment contained in these granules. To date, about a hundred genes are known that are involved in the process of pigment production. Changes in some of them are associated, for example, with such a violation as albinism . However, it has not yet been possible to associate characteristic racial differences in skin pigmentation with any of the genes. Skin pigmentation is of the same nature in other animals.
group led by Keita Chenga (Keith Cheng) at the University of Pennsylvania has dealt with the nature of skin cancer for many years. The work used an aquarium zebra fish (danio rerio, English "Zebrafish"), which has already become a traditional model for genetic research. An unexpected find turned out to be a by-product of the work. The researchers found that a special variety of zebra fish (called golden ones) have smaller and rarer melanosomes with lighter pigment.
A more thorough analysis made it possible to associate this feature with a mutation, as a result of which one of the proteins, called slc24a5 , is synthesized in a reduced form, which leads to changes in pigmentation, according to the PhysOrg website. When zebra goldfish were injected with normal protein, they regained their normal coloration. But the most interesting thing was that the gene responsible for the synthesis of this protein is present in almost all vertebrate animals, including humans. Moreover, it has never been associated with the mechanisms of pigmentation before.
To finally deal with this find, Keita Cheng turned to his colleague Mark for help. 
Shriver (Mark Shriver), who specializes in human evolutionary genetics and the physiology of pigmentation.
Starting with a database of human HapMap variations, the researchers found one of the positions in the same gene that caused color changes in the fish (called SNP - single nucleotide polymorphism). Moreover, in the inhabitants of West Africa and East Asia, in this position, this gene is exactly the same as in other vertebrates, including chimpanzees and zebra fish, and in Europeans, a difference of only one nucleotide was found.
To make sure that the found mutation is related to skin color, Shriver analyzed the presence of this mutation in mestizos - descendants of interracial marriages. The results showed that people who carry the European version of the gene tend to have lighter skin than those who carry the ancient variant. As a result, the researchers concluded that the contribution of the identified mutation to the determination of human skin color ranges from 25 to 38%.
The group believes that racial differences in eye and hair color in Caucasians may also be due to a variation in the SLC24A5 gene, but differences in skin color in East Asians are due to changes in other genes that have not yet been discovered. It is assumed that this mutation in Europeans is adaptive. Pigmentation reduction is necessary in order to maintain sufficient levels of vitamin D synthesis in the skin in conditions of reduced sunlight, which prevents the development of rickets.
People are different: black, white, and also brown: from light to dark. Skin color varies from continent to continent. Where did this diversity come from? What does a person depend on? What is melanin? Let's figure it out.
Melanin. What's this?
In medical terms, melanin is synthesized in skin cells called melanocytes. Interestingly, it is present in the bulk of animals, including humans. It is the pigment melanin that gives the skin a variety of shades. It is synthesized in two leading forms that range in color from yellow to dark brown to black. Eumelanin is the form of melanin that gives skin its brown color. The second form of melanin is pheomelanin, which has a reddish-brown hue. Thanks to pheomelanin, people have freckles or fiery red hair.
Today almost everyone knows about genetics. Each of us has inherited a set of chromosomes from our parents, including those responsible for human skin color. The more active genes in the cells, the darker the skin color. Not so long ago it was possible to observe a unique case in one family where twins with different skin colors were born. But in addition to the genetic predisposition, external factors also influence the production of melanin.
The impact of melanin on humans
Any person on our planet has an approximately equal number of melanocytes. This fact proves that all people on the planet, whether white men or black girls, have the same skin. The question arises in the synthesis of melanin by a separate organism and some external factors. Under the influence of ultraviolet radiation, human skin begins to produce more melanin. This helps prevent DNA damage in human skin.
Until now, this process has not been fully explored, but thanks to the protective reaction of the body, our skin remains intact. And in people living in the equatorial region, where the sun's rays scorch ruthlessly, the skin has acquired its characteristic swarthy color.
Crash in the program
But unfortunately, there are exceptions to the rules. Today you can observe a rare disease - albinism. It is characterized by the absence of melanin in the skin cells. This process is observed in both animals and humans. We are happy to watch snow-white animals, for example, you can see or magnificent, but if this happens to a person, this is really a tragedy. A person cannot stay in the open sun for a long time, his skin burns instantly. The body suffers from strong radiation.
There is another failure in the genetic program caused by the progressive loss of melanocytes - vitiligo. In this case, the skin becomes patchy. Whatever color of a person's skin prevails, with this disease it becomes completely white in places. And as a result, a dark-skinned person by nature can become completely white. Unfortunately, today genetic failures are incurable.
Light-skinned inhabitants of the planet
An interesting fact is that representatives of the white population make up 40% of all mankind. As we have already said, the genetically light color of human skin is due to the activity of melanin in the cells. If we take into account that the people who settled on the planet had facial features and dermis color characteristic of a certain group, then over time the isolation of the group led to the formation of a light-skinned race. The bulk of these people live in Europe, Asia and North Africa.
Human skin color, as already mentioned, also depends on external factors. For example, people in Northern Europe have lighter skin than Asians. are less active in the north, and therefore it is easier for white people to get the vitamin D they need. Although it should be noted that there are northern peoples who have enough. According to scientists, this also depends on food.
Interestingly, in people with fair skin, melanin in the upper layers of the epidermis is present in single copies. Eye color also depends on which layer of the iris contains a large amount of melanin. If this is the first layer, then the eyes will be brown, and if the fourth or fifth layers, then, respectively, blue or green.
black people
The main population with dark skin color lives in Central and South Africa. People in this climate zone are exposed to intense solar exposure. And exposure to ultraviolet radiation causes the synthesis of melanin in the human body, which has a protective function. Dark skin is the result of constant exposure to the sun.
A distinctive feature at the gene level in people with black skin is that their cells produce melanin in large quantities. In addition, as scientists have found out, the top layer of the epidermis in such people completely covers the skin with pigment. This fact gives the skin a color that ranges from brown to almost black.
An interesting fact is that the pigment melanin appears in humans even in embryonic development. But by the time of birth, melanocytes practically disappear from the baby's body, and after birth they begin to develop intensively in the skin. Many people are surprised when they see light-colored babies from a dark-skinned mother. The fact is that children are born light and darken over the next few months.
In conclusion
At present, science is based on the fact that human skin color is the result of the adaptation of a certain group of people to the intensity of solar radiation in their habitat. Melanin in this case performs protective functions from the ultraviolet radiation of the sun, in the absence of it, the skin would become decrepit very quickly. In addition to aging, the possibility of skin cancer increases.
Interestingly, women have lighter skin than men. This is why black girls look much lighter than guys. In people with a light dermis, this difference is practically not noticeable. Unfortunately, in today's world, skin color often gives rise to stereotypes. The division of mankind on this basis often leads to But after all, we all belong to the same species and are people.
The skin color of each person is different, to say nothing of racial differences. And all this is provided by the pigment melanin, which is produced by special cells - melanocytes. Melanocytes are found in the lower layers of the epidermis. Melanin is responsible not only for coloring the skin, but also for the color of the eyes and hair. Blood vessels also determine the color of the skin: the pallor or redness of the skin depends on their expansion / narrowing.
http://training.seer.cancer.gov/ss_module14_melanoma/unit02_sec02_anatomy.html
The skin of different areas of the skin contains different amounts of melanin. The palms and feet are devoid of melanin - in these areas the skin is the lightest. In the area of ββββthe nipples and scrotum in men, the concentration of melanin is increased, so these areas are colored darker than the rest of the skin. Melanocytes are found not only in the skin, but also in the inner ear, retina and vascular layer of the eye.
Once upon a time, all people were dark-skinned, and only as they moved north, a gene mutation was fixed, providing an increasingly lighter skin tone for better synthesis of vitamin D. Now there is a type of mutation in which melanin is completely absent - such albinos have very light skin and hair .
What determines the amount of melanin
The number of melanocytes in all people is about the same, but the amount of melanin produced varies greatly. It depends on genetic characteristics, the intensity of UV radiation, and also on gender (the skin of women is on average 3-4% lighter than that of men).
When exposed to the sun, the production of melanin increases. This is necessary for UV protection. The more melanin is produced, the darker the skin becomes - a tan appears. The paler the original skin, the lower the protective capabilities of melanin. This is why sunburn occurs with excessive exposure to the sun. Having too many sunburns in a lifetime increases the risk of skin cancer.
The synthesis of melanin is stimulated not only by the action of ultraviolet radiation, but also by hormones (melanostimulating hormone and ACTH). In old age, there is a decrease in the production of hormones, as a result of which the production of melanin decreases, the skin becomes lighter - the risk of sunburn and the development of skin cancer increases.
Melanoma
Malignant degeneration of melanocytes causes melanoma - one of the fastest types of cancer with a very high mortality (80% of deaths from skin cancer occur in melanoma).