This report discusses the methodology and findings from a research study to determine trait patterns in hair morphology and ultrastructure among three biogeographically defined metapopulations, with the goal of developing a better understanding of human hair form variation and establishing a foundation for future research on the genetic and developmental bases of phenotypic variation in hair ultrastructure related to genotype.
Human scalp hairs are often examined microscopically to study the variation and diversity among a range of visible morphological traits. In this study, the authors focused on the ultrastructure of human scalp hair within its keratinized matrix, emphasizing, the density and distribution of melanosomes, variation in cuticle thickness within populations, and the relationship of hair fiber ultrastructure with biogeographic ancestry. The authors used transmission electron microscopy (TEM) to visualize hair cross-sections and generate micron-scale resolution images for analysis of particle morphology and the layered hair matrix. Their results revealed considerable variation in all parameters examined, including the relationship of ultrastructure to biogeographic ancestry. Among the three metapopulations studied (European, African, and East Asian), they identified hair cross-sectional shape, cuticle dimensions, and melanosome distribution as traits that reveal statistically significant ancestry-related patterns. This study establishes trait patterns in hair morphology and ultrastructure among three biogeographically defined metapopulations to improve the current understanding of human variation in hair form and establish a foundation for future studies on the genetic and developmental bases of phenotypic variation in hair ultrastructure related to genotype. (Published Abstract Provided)