Each person receives half of their genes from one of their two parents and the other half from the other parent, combining to generate a individual set of genes. Although most of these genes are very similar between different people, each one has its own combination. Even among members of the same family, genetic variability can be enormous.

Although this great variability makes it impossible to predict most aspects that a person will develop, among other things due to the great influence of the environment and lifestyle, genetic research has made it possible to decipher how some genes of parents, grandparents and great-grandparents can influence future generations , including some genes that affect hair color.

What determines hair color?

The hair is basically made up of keratin and its color is due to the addition of other substances of a phenolic nature known as a whole as melaninthe same substance that melanocytes produce and that give rise, among others, to the color of the skin.

There are two main types of melanin, the group of eumelaninsformed by oxidation of tyrosine, and the pheomelanins, formed by sulfur compounds conjugated with tyrosine. Eumelanins are black and brown in color; pheomelanins are red. The final color is the result of mixing all of them; In general, the greater the amount of eumelanins, the darker the color of the hair and, conversely, the greater the amount of pheomelanins, the lighter the color of the hair.

A low concentration of brown eumelanin gives rise to blonde hair, while a large amount of this melanin will give rise to chestnut or brown hair. A much higher amount of black eumelanin will result in brunette, dark brown or black hair.

Hair color, although it is a characteristic generally associated with the personal traits of an individual, is not usually constant throughout life, since the ability to produce melanin from the melanocytes of the hair bulbs changes at different vital stages. . For example, at advanced ages, melanocytes lose their ability to synthesize melanin and hair turns gray or white.

hair color genetics

The genetics of hair color have not been established with complete certainty, but observations suggest that it is governed by Mendelian inheritance patterns, that is, with the participation of dominant alleles and recessive alleles.

Each person has two copies of each gene. Each copy is called an allele, and each is inherited from one parent. The allele for blonde color causes a change in Tyrosinase-Related Protein-1 (TYRP1 gene) that affects its catalytic capacity, which results in increased amount of pheomelanins and in the development of the blonde phenotype.

When a person has one copy of the blonde allele and one copy of the brown allele, the catalytic ability is offset by expression of the brown allele, creating a recessive inheritance pattern for the blonde phenotype.

This means that a person is blonde only if the two copies they have are of the blonde allelewhile it can be brown or brunette even if it has only one copy for the color brown (if one copy is brown and the other is blonde, the phenotype is brown).

These inheritance patterns explain how a couple of dark parents can have blonde children. Each of the brown parents may have one brown allele and one blonde allele, and since each parent passes on half of their genetic information, it may be that one offspring inherits two blonde alleles.

Thus, a dark-haired couple can have a blonde daughter or son. Now, for this to happen, both parents have to have the blonde allele in addition to the brown one, that is, they would have to be heterozygous for the hair color gene. If any of them is homozygous brown, that is, with the two brown alleles, it will pass the brown color to 100% of the offspring, and being a dominant allele, 100% of its offspring would also be brown.

In addition to the brown, dark and blonde phenotypes, there are other phenotypes in which genetic inheritance is involved, such as the red-haired phenotype.