Quantitative assessment of skin, hair, and iris variation in a diverse sample of individuals and associated genetic variation

Abstract

The quantitative methods used here provide a fine-scale assessment of pigmentation phenotype and facilitate genotype-phenotype associations, even with relatively small sample sizes. This represents an important expansion of current investigations into pigmentation phenotype and associated genetic variation by including non-European and admixed populations. Am J Phys Anthropol 160:570-581, 2016. © 2015 Wiley Periodicals, Inc.

Quantifying variation in human scalp hair fiber shape and pigmentation

“…There have been a number of recent publications on the genetic background of hair color variation in Europeans and Melanesians (Graf et al, ; Sulem et al, ; Branicki et al, ; Sturm, ; Kenny et al, ; Norton et al, ), but none on the distribution of hair pigmentation around the world. The identification of phenotypes for some genetic studies is based on categorical descriptions of hair color (e.g., Flanagan et al, ; Branicki et al, ), which may lack the accuracy necessary for revealing relevant genes in non‐European populations (Norton et al, ).…”

“…There have been a number of recent publications on the genetic background of hair color variation in Europeans and Melanesians (Graf et al, ; Sulem et al, ; Branicki et al, ; Sturm, ; Kenny et al, ; Norton et al, ), but none on the distribution of hair pigmentation around the world. The identification of phenotypes for some genetic studies is based on categorical descriptions of hair color (e.g., Flanagan et al, ; Branicki et al, ), which may lack the accuracy necessary for revealing relevant genes in non‐European populations (Norton et al, ). Reflectance spectrophotometry, as a quantitative method of assessing hair pigmentation, has been applied to a number of genetic studies on hair color variation, successfully demonstrating the contribution of OCA2/HERC2 and IRF4 to European variation in hair pigmentation (Norton et al, ; Shekar et al, ; Candille et al, ).…”

“…The identification of phenotypes for some genetic studies is based on categorical descriptions of hair color (e.g., Flanagan et al, ; Branicki et al, ), which may lack the accuracy necessary for revealing relevant genes in non‐European populations (Norton et al, ). Reflectance spectrophotometry, as a quantitative method of assessing hair pigmentation, has been applied to a number of genetic studies on hair color variation, successfully demonstrating the contribution of OCA2/HERC2 and IRF4 to European variation in hair pigmentation (Norton et al, ; Shekar et al, ; Candille et al, ). The quantification of hair pigmentation in these studies involved the use of a spectrophotometer to measure the reflectance of hair either directly from the scalp (Norton et al, ) or from a hair sample that has been cut (Shekar et al, ).…”

“…Reflectance spectrophotometry, as a quantitative method of assessing hair pigmentation, has been applied to a number of genetic studies on hair color variation, successfully demonstrating the contribution of OCA2/HERC2 and IRF4 to European variation in hair pigmentation (Norton et al, ; Shekar et al, ; Candille et al, ). The quantification of hair pigmentation in these studies involved the use of a spectrophotometer to measure the reflectance of hair either directly from the scalp (Norton et al, ) or from a hair sample that has been cut (Shekar et al, ). While the use of spectrophotometers appears to be successful for detecting the range of variation displayed by European individuals, the use of even more fine‐scale quantitative methods might be warranted for the assessment of non‐European hair pigmentation variation (Norton et al, ).…”

“…The quantification of hair pigmentation in these studies involved the use of a spectrophotometer to measure the reflectance of hair either directly from the scalp (Norton et al, ) or from a hair sample that has been cut (Shekar et al, ). While the use of spectrophotometers appears to be successful for detecting the range of variation displayed by European individuals, the use of even more fine‐scale quantitative methods might be warranted for the assessment of non‐European hair pigmentation variation (Norton et al, ). It is possible to estimate the total melanin (TM) content of a small sample of solubilized hair through spectrophotometric analysis (Ozeki et al, ; Commo et al, ).…”