TCHH rs72921006: What Your Genotype Means
The rs72921006 variant is a genetic marker located within the TCHH gene, which plays a role in the structural development of hair. Research suggests this variant is associated with variations in hair morphology, such as straight, wavy, or curly hair, particularly in individuals of European ancestry.
What each genotype means
Typical hair curl tendency
You carry two copies of the common ancestral C allele for this variant in the TCHH gene. In genome-wide association studies of European populations, this genotype is less associated with straight hair and corresponds to the baseline likelihood of having wavy or curly hair. Hair shape is a complex polygenic trait, meaning multiple other genetic and environmental factors also contribute to your final hair texture.
Found in approximately 40% to 45% of individuals of European descent, and at significantly higher frequencies in non-European ancestries.
Moderate straight hair tendency
You carry one copy of the derived T allele associated with straighter hair in the TCHH gene. Population studies indicate that having one copy of this allele shifts hair morphology toward straight or wavy patterns relative to the CC genotype. However, because hair texture is governed by multiple genes, this variant accounts for only a modest fraction of overall hair morphology variation.
Carried by approximately 45% of individuals of European descent, but relatively rare in East Asian and African populations.
Increased straight hair tendency
You carry two copies of the derived T allele in the TCHH gene. Research in European populations shows that individuals with two copies of this allele have the highest statistical probability of having naturally straight hair among the genotypes for this variant. Because hair curliness is influenced by multiple interacting genes, carrying this genotype does not guarantee straight hair.
Found in roughly 10% to 15% of people of European descent; it is very rare or absent in populations of East Asian and African ancestry.
Understanding the SNP and Its Location
The variant rs72921006 is a single nucleotide polymorphism (SNP) situated within the TCHH gene. This gene is located on chromosome 1. In genetics, a SNP represents a variation at a single position in the DNA sequence among individuals. While the human genome is remarkably similar across all people, these small variations can contribute to differences in physical traits. The TCHH gene is specifically involved in the biological processes that occur within the hair follicle, the structure from which hair grows. By studying markers like rs72921006, researchers aim to understand the genetic architecture that influences human physical characteristics, such as hair texture, which varies significantly across different global populations.
The Role of the TCHH Gene
The TCHH gene provides the instructions for producing a protein called trichohyalin. This protein is essential for the structural integrity of hair. Once produced, trichohyalin is modified to bind with other proteins and keratin intermediate filaments, creating a dense, organized network. This network is what gives the hair shaft its cylindrical shape and strength. When the TCHH gene functions normally, it helps ensure that hair develops with a consistent structure. Disruptions or variations in this gene can alter how these cross-links form, which may influence the final shape of the hair shaft. While extreme mutations in TCHH are linked to rare conditions like uncombable hair syndrome, common variants like rs72921006 are thought to contribute to the natural spectrum of hair textures seen in the general population.
Research and Evidence Strength
Scientific research has identified associations between variants in the TCHH gene and hair morphology in populations of European descent. Genome-wide association studies have highlighted the TCHH region as a significant contributor to the variance in hair texture, explaining a portion of the differences observed between straight, wavy, and curly hair. However, it is important to note that the evidence for any single SNP, including rs72921006, is often considered limited in terms of its individual predictive power. Hair texture is a complex, polygenic trait, meaning it is influenced by the combined effects of many different genes and environmental factors. Therefore, while this variant is statistically associated with hair form, it is only one piece of a much larger and more complex genetic puzzle.
Interpreting Your Genetic Information
Information regarding genetic variants like rs72921006 is intended for educational purposes to help you understand the science of human traits. It is important to recognize that genetic associations are based on statistical trends observed in large groups of people and cannot definitively predict an individual's physical appearance. You cannot use this information to diagnose any health condition or to make medical decisions. If you have concerns about your hair or scalp health, or if you are interested in how genetics might influence your personal traits, it is best to consult with a qualified healthcare professional or a dermatologist. Genetic data provides a fascinating glimpse into our biological makeup, but it should always be viewed as a supplement to, rather than a replacement for, professional medical advice.
How common is this variant?
The minor allele frequency for variants in the TCHH gene is approximately 0.35 in European populations, where these markers are most frequently studied.
Frequently asked questions
Does this variant determine if I have curly or straight hair?
No, this variant does not determine your hair texture on its own. Hair texture is a complex trait influenced by many different genes and environmental factors, and this SNP only accounts for a small portion of that variation.
Can I use this information to predict my children's hair type?
Genetic associations are based on statistical probabilities across large populations and are not reliable for predicting individual traits in family members. Many genetic and environmental factors contribute to hair texture, making it impossible to predict based on a single SNP.
Is this variant linked to any medical conditions?
While the TCHH gene is involved in hair structure, this specific variant is primarily studied in the context of natural variation in hair texture. It is not typically associated with medical disorders.
Where can I learn more about my own genetic data?
If you have received genetic testing results, you should review them with a genetic counselor or your primary healthcare provider. They can help you interpret the information in the context of your personal and family health history.
Sources & further reading
Educational information only, last refreshed 10/18/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Common polymorphism in the trichohyalin locus strongly predictive of straight versus curly hair texture morphology in Europeans.
Key genetic variant within trichohyalin that shapes hair curliness, wave pattern, and texture in individuals of European ancestry.
Trichohyalin variant associated with hair curliness in individuals of European descent.
Missense coding variant in trichohyalin that plays a major determinant role in human straight versus curly hair morphology.
Variant in the TCHH gene associated with variation in hair curl structure.
Trichohyalin gene variant associated with straight versus curly hair morphology and texture differences in populations of European descent.