Two hair histological variables, the incidence of medullation and diameter, have been dealt with in twelve populations belonging to different ethnic groups and living in different geographical areas. Results of the F test comparing within-individual variance, between-individual variance and between-population variance of the hair variables concerned indicate that differentiation of various populations is possible. Sex differences for medulla and diameter of hair are observed in some populations included in the present study.
The genetic basis of scalp hair histomorphological variables, such as incidence of medulla, diameter, area of cross-section, cross-sectional index, and weight has been examined in a Bengalee hair sample (India) by family study. The results of correlation analysis between different combinations of parents and offspring together with sibs indicate the involvement of a significant genetic component in variability. The estimates of heritability based on regression coefficients of parent--child are 0.725 (incidence of medullation), 0.534 (diameter), 0.466 (area of cross-section), 0.673 (cross-sectional index), and 0.369 (weight). Moreover, there is little evidence of X-linkage involved in the hair variables.
Data on the incidence of medulla of human head hair based on 9,600 strands examined from 48 pairs of zygosity--determined German twins were quantified as medullary ratio and subjected to variance analysis to give information about genetic significance of the character concerned. The results of F test and heritability estimate yielded significant values indicating the presence of a strong genetic component of variability in the incidence of medulla of human head hair. Sex influence upon the character is found to be absent.
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