I am grateful to members of my laboratory and colleagues who study pigment cells in a variety of different experimental organisms for useful discussions and to Sophie Candille for helpful comments on the manuscript. Skin color has always been a (dumb) reason for discrimination and many racial rifts. (A) A traditional skin color map based on the data of Biasutti. Differences in emotional stability cause individual differences. The underlying assumption is that if a rare null allele causes a complete loss of pigment, then a set of polymorphic, i.e., more frequent, alleles with subtle effects on gene expression will contribute to a spectrum of skin colors. There are three ways people can end up with different skin color. Data have been collected only for MC1R, in which the most notable finding is a dearth of allelic diversity in African samples, which is remarkable given that polymorphism for most genes is greater in Africa than in other geographic regions (Rana et al. More important than the ratio of melanin types is the total amount of melanin produced. Describe the mechanisms of hair production, and explain the structural basis for hair texture and color. (B) Summary of 102 skin reflectance samples for males as a function of latitude, redrawn from Relethford (1997). Oddly enough, even Darwin was wrong on skin color. However, two forms are produced--pheomelanin, which is red to yellow in color, and eumelanin, which is dark brown to black. At the other end of the spectrum, inadequate exposure to sunlight, leading to vitamin D deficiency and rickets, has been mostly cured by nutritional advances made in the early 1900s. | Skin color is Continuous: Mean (dot) and s.d. here. (bar) of skin color, for 22 populations Biological Determinants of Skin Color •The pigments Carotene, Hemoglobin, and Melanin are involved in skin color •Carotene, the least common skin pigment results in a yellowing of skin –Results primarily from the over-consumption of For example, Sarah's work supports the hypothesis that lighter skin in climates further away from the sun gave an individual a selective advantage (because their skin was able to make more vitamin D and avoid diseases like rickets). From a clinical perspective, inadequate protection from sunlight has a major impact on human health (Armstrong et al. Explain how the skin responds to injury and is able to repair itself. An important caveat is that we do not know how patterns of UV irradiation have changed over time; more importantly, we do not know when skin color is likely to have evolved, with multiple migrations out of Africa and extensive genetic interchange over the last 500,000 years (Templeton 2002). Regardless, most anthropologists accept the notion that differences in UV irradiation have driven selection for dark human skin at the equator and for light human skin at greater latitudes. Melanin and Your Skin. © 2003-2021 Chegg Inc. All rights reserved. 2003). From these perspectives, oxidative enzymes like tyrosinase (TYR), which catalyzes the formation of dopaquinone from tyrosine, or melanosomal membrane components like the pink-eyed dilution protein (P) or the membrane-associated transporter protein (MATP), which affect substrate availability and activity of TYR (Orlow and Brilliant 1999; Brilliant and Gardner 2001; Newton et al. And, finally, should we care about the genetics of human pigmentation if it is only skin-deep? 1969; Toda et al. Many of the ideas presented here emerged during a discussion series on Unsolved Mysteries in Biomedical Research that was initiated by Mark Krasnow and the Medical Scientist Training Program at Stanford University. View desktop site, 2. Except for albinos, we all have the same amount of melanocyte cells in our bodies. For more information about PLOS Subject Areas, click PLoS Biol 1(1): According to conservative estimates, there is a 3-fold incidence of sarcoidosis in individuals of African vs European descent. Explain and list the ABCDE rule of skin cancer. 2000). Each pigment cell actively transfers its melanosomes to about 40 basal keratinocytes; ultimately, skin reflectance is determined by the amount and distribution of pigment granules within keratinocytes rather than melanocytes. Statements regarding the number of human skin color genes are attributed to several studies; one of the most complete is by Harrison and Owen (1964). It is important to accurately define an individual’s skin color, an important modifier of received UV radiation dose, to determine sunburn susceptibility, which is a key risk factor for melanoma. In this article, learn more about the types of vagina and when the appearance can indicate a health issue. Yes Yes Thus, at least one component of skin color variation represents a gene or genes whose expression and action affect the pigment cell environment rather than the pigment cell itself. These cells are found in the epidermis of your skin. The version has of each of these genes work together to create the final product -your skin color. At 2 ½ or so, children learn gender labels (boy/girl) and the name of colors – which they begin to apply to skin color. E. Explain why a healthy 6-month-old might have yellow-orange skin. by Lawrence R. Tenzer October/November 2000. In Australia, the lifetime cumulative incidence of skin cancer approaches 50%, yet the oxymoronic “smart tanning” industry continues to grow, and there is controversy over the extent to which different types of melanin can influence susceptibility to ultraviolet (UV) radiation (Schmitz et al. From a basic science perspective, variation in human skin color represents an unparalleled opportunity for cell biologists, geneticists, and anthropologists to learn more about the biogenesis and movement of subcellular organelles, to better characterize the relationship between genotypic and phenotypic diversity, to further investigate human origins, and to understand how recent human evolution may have been shaped by natural selection. Terms (1972), and Konrad and Wolff (1973) based on individuals whose recent ancestors were from Africa, Asia, or Europe. 1999; Harding et al. Its amazing to realize that most of this color is attributed to a single class of pigments: the melanins. Is the Subject Area "Skin" applicable to this article? Support surface interventions (National Pressure Ulcer Advisory Panel and European Pressure Ulcer Advisory Panel, 2009). More recent studies by physical anthropologists have substantiated and extended these observations; a recent review and analysis of data from more than 100 populations (Relethford 1997) found that skin reflectance is lowest at the equator, then gradually increases, about 8% per 10° of latitude in the Northern Hemisphere and about 4% per 10° of latitude in the Southern Hemisphere. 7. This brings us to the question of candidate genes for skin color, since, like any quantitative trait, a reasonable place to start is with rare mutations known to cause an extreme phenotype, in this case Mendelian forms of albinism. To capture skin tone accurately, they used a color meter to measure the light reflectance on each individual’s inner arm, where the sun is least likely to alter the natural skin color. Lighter skin tones are considered preferable in many countries in Africa, Asia and South America. Scientists call this “different effect size.” PLOS Biology 1(3): e91. Yes Chapter Seven of “A Completely New Look At Interracial Sexuality”. 1998; Rees 2000) However, MC1R variation has a significant effect on pigmentation only in populations where red hair and fair skin are common (Rana et al. 1999; Harding et al. Skin assessment; 3. Your ancestors' skin color has the biggest influence on your skin tone, which is determined by the biological factor of genetics. Sometimes One Gene is Stronger than the Others Sometimes a particular gene can have a much bigger effect than other genes. (A) Activation of the melanocortin 1 receptor (MC1R) promotes the synthesis of eumelanin at the expense of pheomelanin, although oxidation of tyrosine by tyrosinase (TYR) is required for synthesis of both pigment types. In addition, histological characteristics of different-colored skin provide some clues as to cellular mechanisms that are likely to drive pigmentary variation (Figure 1B). An alternative approach for considering the number of potential human pigmentation genes is based on mouse coat color genetics, one of the original models to define and study gene action and interaction, for which nearly 100 different genes have been recognized (Bennett and Lamoreux 2003; Jackson 1994). Current debates in the human genetics community involve strategies for selecting populations and candidate genes to study, the characteristics of sequence polymorphisms worth pursuing as potential disease mutations, and the extent to which common diseases are caused by common (and presumably ancient) alleles. Aside from the key word minimal (Harrison and Owen's data could also be explained by 30–40 genes), one of the more interesting findings was that skin reflectance appeared to be mainly additive. These variations in skin color are due to differences in the amount and distribution of melanin in the epidermis. Recent developments in several areas provide a tremendous opportunity to better understand the diversity of human pigmentation. Remarkably, keratinocytes from dark skin cocultured with melanocytes from light skin give rise to a melanosome distribution pattern characteristic of dark skin, and vice versa (Minwalla et al. The presence of freckling and benign nevi also indicates an increased risk for melanoma development. Yes In any case, a risk for vitamin D deficiency can only explain selection for light skin. The most popular theory posits that protection offered by dark skin from UV irradiation becomes a liability in more polar latitudes due to vitamin D deficiency (Murray 1934). This diagram is based on one published by Sturm et al. Yes Explain what accounts for individual differences in skin color and compare basal cell carcinoma with malignant melanoma. 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