Terminal Hair Phenotypes

 Terminal Hair Phenotypes

Not all terminal hairs have the same cross sectional appearance (Phenotype). The phenotype of the first modern humans is unknown, but recent genomic work is identifying when major mutations occurred resulting in current regional hair forms.

Terminal hairs have traditionally been described as round, oval or flat. In reality there is broad spectrum of hair shapes, and although individuals tend to bear essentially one type on their scalps, it has been observed that all three can be present. The phenotype is determined by genetic inheritance, and more than one from can be seen on single head more commonly with increasing genetic diversity due to the easing of social and ethnic barriers in societies. 

 

 

While peoples from subequatorial Africa and their dispersed descendants have hair follicles which are curved, the final shape of the hair emerging from the follicle is determined more by the activity of the matrix cells deep in the follicle and the manner in which the keratin proteins are laid down in the cortex.

 

The hypothesis that hair shaft shape is principally due to the shape of the follicle is further confounded by the ability of terminal hair follicles to produce different phenotypes under altered circumstances. After chemotherapy, patients routinely report dramatic change in hair shaft phenotypes, presumably due to a change in arrangements of keratins in the cortex from a re-programmed matrix.