Hair loss and Genes

Hair loss and Geness
Common baldness cannot occur without the presence of specific inherited genes. These genes can be passed on by either parent. A gene is a single bit of chemically encoded hereditary instruction that is located on a chromosome and actually represents a tiny segment of DNA. Chromosomes occur in pairs (humans have 23 pairs), and every individual gets one set of chromosomes from each parent. Hair loss in men is now felt to involve more than one gene. When several genes govern a trait, it is called polygenic.

Genes that are located on the X or Y-chromosomes are call sex-linked. Genes on the other 22 pairs of chromosomes are called autosomal. It is felt that the genes governing common baldness are autosomal (not sex linked). This means that the baldness trait can be inherited from the mother’s side of the family or the father’s side with equal frequency. The commonly held notion that baldness comes only from the mother’s side of the family is incorrect, although for reasons not fully understood, the predisposition inherited from an affected mother is of slightly greater importance than that inherited from an affected father.

The term, “dominant” means that only one gene of a pair is needed for the trait to show up in the individual. A “recessive” gene means that both genes need to be present in order for the trait to be expressed. The genes involved in balding from androgenetic alopecia are felt to be dominant.

Just because one has the genes for baldness, it doesn’t mean the trait will manifest itself. The ability of a gene to affect one’s characteristics, i.e. be visible in a particular individual, is called “expressivity”. Gene expression is related to a number of factors, the major ones being hormones and age, although stress and other factors can be reasons for hair loss and balding in some individuals.

It is of interest that, although genes for some types of male hair loss have been mapped, none of the genes for male pattern baldness have yet been identified. This suggests that any kind of genetic engineering to prevent common baldness is still many years away.