Our hair, with its diverse colors, textures, and even its tendency to thin, is largely shaped by our genetic blueprint. Hair genes are DNA segments that carry instructions for hair growth and characteristics. These genetic instructions are passed down from our parents, influencing the unique traits of our hair. The specific combination of these genes determines everything from the shade of our strands to their natural curl pattern and how they might change over time.
How Hair Genes Are Inherited
Our genetic makeup, including the genes that influence hair traits, is organized into structures called chromosomes. Humans typically have 23 pairs of chromosomes, with one set inherited from each biological parent, providing a unique combination of genetic instructions. Within these chromosomes, specific stretches of DNA form genes, which carry the codes for various traits. For hair characteristics, multiple genes often work together in a complex interplay, rather than a single gene dictating a trait. This is known as polygenic inheritance. As an example, if one parent contributes genetic information for straight hair and the other for curly hair, a child might inherit a blend that results in wavy hair.
The Genes Behind Hair Color
Hair color comes from pigments called melanin, produced by specialized cells called melanocytes within hair follicles. There are two primary types of melanin: eumelanin, which provides black and brown hues, and pheomelanin, responsible for red and yellow tones. The specific color of hair depends on the amount and ratio of these two melanin types. For instance, abundant eumelanin leads to black or brown hair, while a high concentration of pheomelanin results in red hair.
A significant gene influencing hair color is MC1R, or Melanocortin 1 Receptor. This gene provides instructions for a protein that controls the type of melanin produced by melanocytes. When the MC1R receptor is active, it promotes the production of eumelanin, leading to darker hair. If the receptor is less active or blocked, melanocytes produce more pheomelanin, resulting in lighter or red hair. Variations in the MC1R gene are strongly linked to red hair.
The Genes Behind Hair Texture and Type
Hair texture, whether straight, wavy, or curly, is largely determined by the shape of the hair follicle from which the hair strand grows. A round hair follicle tends to produce straight hair, while oval-shaped follicles lead to wavy hair. The curlier the hair, the more oval or even flat the hair follicle’s cross-section. This follicle shape is a genetically influenced trait.
Specific genes have been identified that play a role in determining hair texture. For example, the EDAR gene influences the development and growth of hair follicles, impacting hair thickness and density. Variations in this gene can lead to differences in hair thickness, with some variants associated with thicker hair strands. Other genes, such as the Hr gene and various KRT genes, influence the shape of hair follicles and the protein structure of hair, affecting curl patterns and overall texture. The interaction of these multiple genes, inherited from both parents, contributes to the unique texture of an individual’s hair.
Genetic Influences on Hair Loss
A common form of hair loss, particularly in men, is androgenetic alopecia, often referred to as pattern baldness. This condition has a significant genetic component and is influenced by multiple genes inherited from both sides of the family. While often colloquially linked to the mother’s father, the genetic predisposition is more complex and involves contributions from both maternal and paternal genes. Studies indicate that genetics account for a substantial portion of male pattern baldness, with some estimates suggesting around 80%.
A key gene implicated in androgenetic alopecia is the Androgen Receptor (AR) gene, located on the X chromosome, which males inherit from their mothers. Variations in the AR gene can lead to hair follicles that are more sensitive to hormones called androgens, specifically dihydrotestosterone (DHT). This heightened sensitivity can cause hair follicles to shrink and produce thinner, shorter hair, eventually leading to hair loss. Beyond the AR gene, other genes, such as SRD5A2, which is involved in converting testosterone to DHT, and genes like WNT10A, EDA2R, HEPH, CEPT1, and EIF3F, also contribute to the variability and progression of pattern hair loss.