The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)

Skin, hair, and iris pigmentation: quantifying phenotype and identifying genetic loci associated with variation in diverse populations


1Department of Anthropology, University of Cincinnati, 2Department of Anthropology, University of Toronto, Mississauga

March 26, 2015 , Gateway Ballroom 2 Add to calendar

Characterizing skin, hair, and iris pigmentation and understanding the genetic architecture underlying this phenotype is of interest to the fields of anthropology, evolutionary biology, and forensic science. Compared to European populations, we know little about patterns of variation in non-European and admixed populations or the genetic variants that contribute to this diversity. Here we describe quantitative estimates of pigmentation in large samples of European, East Asian, South Asian, Hispanic, and African American ancestry. Skin and hair pigmentation were measured as M (melanin) index using a DSM II reflectometer. Iris pigmentation was quantitatively assessed from digital photographs and translated into CIELAB color space using novel methods. We observe significant variation among populations in skin (F = 543.8, p < 0.0001) and hair (F = 164.6, p < 0.0001). Mean skin pigmentation is lightest in Europeans (M = 35.4, SD = 3.1) and East Asians (M = 38.0, SD = 2.9), while South Asians (M = 47.5, SD = 6.1) and the admixed African American (M = 64.6, SD = 11.9) and Hispanic (M = 41.6, SD = 7.5) populations are darker and more variable. Analysis of a subset of samples indicates that variation in iris color, including in East and South Asian irides (categorically described as “brown”), can be quantitatively described using CIELAB values. We argue that this refinement in phenotype characterization will increase our power to detect genetic loci with small effects and highlight as examples loci identified as influencing skin and iris pigmentation in East Asians.

This work was supported by funding from NSERC of Canada (Discovery Grant to EJP, doctoral scholarship to ME), and the US Department of Justice (grant 2013-DN-BX-K011 to HLN and EJP).