The Genetics of Mid-Digital Hair Growth: Why Hair Grows On the Middle Segments of the Fingers

Genetics of Appearance

The interesting aspect of science is that it allows you to see the world in a very different way. Every single question which you had as a child, bugged your parents with, all start to unravel with great joy once you hold up the looking glass of science. Much of human behavior and physicality carries some aspect of genetics. There are genes that control and regulate the physical traits that we carry and exhibit, and getting to know them is an interesting adventure.

Autosomal Inheritance

Did you know that you’re ability to roll your tongue is genetically determined? And the position of your thumb when you interlock your fingers is also to some extent written in your genes.

The human genome consists of 23 pairs of chromosomes that provide the blueprint for the complete living being. Out of these there are two chromosomes, called the sex chromosomes, that determine our sex, and the rest are called autosomes. And inherited traits can be classified as autosomal dominant and autosomal recessive.

When a single allele is required for the expression of a physical feature, the trait is said to be autosomal dominant, and when two alleles are required the trait is said to be autosomal recessive. Almost 450 human traits have been classified as autosomal dominant and 500 as autosomal recessive. The dominant and recessive characteristics follow the Mendelian laws of genetic inheritance.

Mid-Digital Hair Genetics

The genetics of mid-digital hair is a curious but interesting phenomenon. Since many physical features of the human body are determined by the autosomes, the genetics behind mid-digital hair is also controlled by them. In a study conducted by Danforth et al in 1921, it was identified that mid-digital hair was a dominant trait.The presence of mid-digital hair is considered to be a dominant trait and the absence recessive. This means that a single allele is enough to provide the feature of mid-digital hair. The Danforth study was followed up by Bernstein & Burks, who suggested that five multiple alleles (D0,D1,D2,D3,D4) were responsible for mid-digital hair - the subscripts refer to the number of fingers having mid-digital hair - and that a D0D0 genotype would result in the absence of hair.

If one of your parents has mid-digital hair and the other doesn’t then there was a 50% chance that you would have inherited the trait.