QUANTIFYING THE PHENOTYPIC EFFECTS OF GENES, ANCESTRY, AND SEX ON HUMAN SCALP HAIR MORPHOLOGY

Open Access
Author:
Bramel, Emily Eloise
Area of Honors:
Biological Anthropolgy
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Mark Shriver, Thesis Supervisor
  • Timothy Michael Ryan, Honors Advisor
Keywords:
  • hair
  • scalp hair
  • anthropology
  • human genetics
  • population genetics
Abstract:
There have been many studies of comparative anatomy that have focused on hair morphology, and thus, the stark morphological differences in hair between some ancestry groups have already been observed. Yet these studies need to be updated with larger and more comprehensive datasets that also consider differences due to age, sex, and genetic ancestry (instead of regional or self-reported ancestry). This study offers a microscopic analysis of hair samples representing five ancestry groups and provides insight into some of the less understood aspects of human hair morphology. Measurements were made using a transmitted light microscope. The results of this study demonstrate that there is a significant association between ancestry and overall diameter, maximum diameter, and the amount of variance in hair’s diameter. The major results for average diameter when considering ancestry are as follows: East Asian and South Asian hairs are significantly larger in average overall diameter than European, African, and Hispanic hair. For maximum diameter, African hair has a significantly greater max diameter than hair of European ancestry. The coefficient of variance (CoV), which gives an indication of the degree of variation in hair form that is present, was significantly different between almost every ancestry group. Notably, hair of African ancestry has an average CoV that is much higher than all of the other ancestry groups while East Asian hair has an average CoV that is considerably lower than all other ancestry groups. This indicates that there is more variation in diameter throughout the hair of the average African individual and less variation in diameter throughout the hair of the average East Asian individual. Examining sex differences among Europeans, males tend to have a greater average overall diameter, maximum diameter, and CoV than females. This research will lead to future studies in the role genes play in the phenotypic variation of hair morphology.