reading2skincolor - Volume 1 | Issue 1 | Page 019 PLoS...

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Unformatted text preview: Volume 1 | Issue 1 | Page 019 PLoS Biology | Unsolved Mystery What Controls Variation in Human Skin Color? Gregory S. Barsh D iversity of human appearance and form has intrigued biologists for centuries, but nearly 100 years after the term “genetics’’ was coined by William Bateson in 1906, the genes that underlie this diversity are an unsolved mystery. One of the most obvious phenotypes that distinguish members of our species, differences in skin pigmentation, is also one of the most enigmatic. There is a tremendous range of human skin color in which variation can be correlated with climates, continents, and/or cultures, yet we know very little about the underlying genetic architecture. Is the number of common skin color genes closer to F ve, 50, or 500? Do gain- and loss-of- function alleles for a small set of genes give rise to phenotypes at opposite ends of the pigmentary spectrum? Has the effect of natural selection on similar pigmentation phenotypes proceeded independently via similar pathways? And, F nally, should we care about the genetics of human pigmentation if it is only skin-deep? Why Should We Care? ¡rom a clinical perspective, inadequate protection from sunlight has a major impact on human health (Armstrong et al. 1997; Diepgen and Mahler 2002). 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 in¢ uence susceptibility to ultraviolet (UV) radiation (Schmitz et al. 1995; Wenczl et al. 1998). At the other end of the spectrum, inadequate exposure to sunlight, leading to vitamin D deF ciency and rickets, has been mostly cured by nutritional advances made in the early 1900s. In both cases, understanding the genetic architecture of human skin color is likely to provide a greater appreciation of underlying biological mechanisms, much in the same way that mutational hotspots in the gene TP53 have helped to educate 3 society about the risks of tobacco (Takahashi et al. 1989; Toyooka et al. 2003). ¡rom 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. The Color Variation Toolbox Historically, measurement of human skin color is often based on subjective categories, e.g., “moderate brown, rarely burns, tans very easily.’’ More recently, quantitative methods based on re¢ ectance spectrophotometry have been applied, which allow reddening caused by in¢ ammation and increased hemoglobin to be distinguished from darkening caused by increased melanin...
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This note was uploaded on 07/17/2008 for the course EEOB 640 taught by Professor Fuerst during the Spring '05 term at Ohio State.

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reading2skincolor - Volume 1 | Issue 1 | Page 019 PLoS...

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