Androgenetic alopecia (common pattern baldness) is a highly prevalent form of progressive hair thinning affecting millions globally. This condition is driven by genetic predisposition and the action of certain hormones. While a long-standing belief suggests the gene for baldness comes exclusively from the mother’s side, the actual inheritance pattern is far more complex. The mother carries a major genetic influence, particularly for men, but this is only one piece of a larger, polygenic puzzle involving multiple genes from both parents.
The Mother’s Role: X-Linked Inheritance
The popular notion that baldness is inherited from the mother stems from the location of the Androgen Receptor (AR) gene on the X chromosome. Men inherit their single X chromosome exclusively from their mother, meaning any AR gene variant on that chromosome is directly passed to the son. The AR gene is a major predictor of androgenetic alopecia, and its variants can increase susceptibility to hair loss.
The X-linked nature of the AR gene explains why the maternal grandfather’s hair pattern is often used as a rough indicator for a man’s future hair loss. Since a mother has two X chromosomes and passes only one randomly to her son, she may carry an AR gene variant associated with baldness without exhibiting significant hair loss herself.
The AR gene encodes the androgen receptor protein, which mediates the biological actions of androgens like dihydrotestosterone (DHT. Variations in this gene determine how sensitive hair follicle receptors are to circulating androgens. A highly sensitive receptor increases the likelihood of early onset and pronounced hair loss. The AR gene is the most significant single genetic factor identified, but it does not account for the entire genetic risk.
Beyond the X Chromosome: Paternal and Autosomal Contributions
Pattern baldness is a polygenic trait, meaning its expression is influenced by the cumulative effect of many different genes, not just the AR gene. These additional genes are located on autosomes (non-sex chromosomes) and are inherited from both parents. Both maternal and paternal genetic factors work together to influence the risk and progression of androgenetic alopecia.
Genome-wide association studies (GWAS) have identified hundreds of genetic markers across the genome that contribute to the risk of pattern baldness. For example, a 2017 review identified 63 genes involved in male pattern baldness, with only a small fraction located on the X chromosome. Genes located on autosomes, such as those on chromosomes 20 and 3, influence hair loss independently of the AR gene.
The father’s genetic contribution is equally significant and influences the severity and age of onset of hair loss. Studies show that a son has a five to six times higher relative risk of developing pattern baldness if his father also experienced hair loss. The combination of risk alleles inherited from both parents determines the overall genetic predisposition.
The Mechanism: How Genes Cause Hair Loss
Inherited genes dictate the physiological process leading to hair loss, which centers on dihydrotestosterone (DHT). DHT is a potent androgen converted from testosterone by the enzyme 5-alpha reductase. These genes determine the sensitivity of hair follicles to this hormone.
In genetically predisposed individuals, DHT binds to androgen receptors in hair follicles, particularly on the top and front of the scalp. This binding triggers follicular miniaturization, a progressive process that shortens the anagen (active growth phase) of the hair cycle.
As the growth phase shortens, follicles produce increasingly thinner, shorter, and finer hairs. Eventually, affected follicles shrink until they no longer produce visible hair, resulting in pattern baldness. The genetic component determines which follicles are susceptible to this DHT-induced shrinking.