ASCL1 rs11603555: Genetics of Hair Curliness
The single-nucleotide polymorphism rs11603555 is a common genetic variant mapped near the ASCL1 gene region on chromosome 12. Large-scale genome-wide association studies have identified it as a contributor to natural variation in human scalp hair texture, specifically distinguishing straight hair from wavy and curly hair types. While it contributes to hair morphology, it represents normal, benign physical variation rather than a medical condition.
What each genotype means
Associated with hair texture
This genotype is associated with variations in scalp hair curliness and texture. Research indicates that this variant in the ASCL1 region contributes to the polygenic architecture of hair morphology, though individual hair traits are influenced by many other genetic and environmental factors.
Carried by approximately 52% of individuals of European ancestry, based on a minor allele frequency of roughly 0.28.
Associated with hair texture
This genotype is associated with variations in scalp hair curliness and texture. Research indicates that this variant in the ASCL1 region contributes to the polygenic architecture of hair morphology, though individual hair traits are influenced by many other genetic and environmental factors.
Carried by approximately 40% of individuals of European ancestry, based on a minor allele frequency of roughly 0.28.
Associated with hair texture
This genotype is associated with variations in scalp hair curliness and texture. Research indicates that this variant in the ASCL1 region contributes to the polygenic architecture of hair morphology, though individual hair traits are influenced by many other genetic and environmental factors.
Carried by approximately 8% of individuals of European ancestry, based on a minor allele frequency of roughly 0.28.
Genomic Location and the ASCL1 Gene
The single-nucleotide polymorphism rs11603555 resides on chromosome 12, positioned in proximity to the ASCL1 (achaete-scute family bHLH transcription factor 1) gene. ASCL1 encodes a basic helix-loop-helix transcription factor that is classically recognized for guiding early neuronal commitment and neuroendocrine cellular differentiation. Although historically characterized within the developing central nervous system, ASCL1 and its adjacent regulatory elements also function across broader epithelial and follicular development programs. In the human scalp, hair follicles undergo sophisticated cycles of differentiation, curvature establishment, and keratinization. Variants located within noncoding regulatory zones around ASCL1 can modulate the spatial expression or timing of transcription factors, subtly influencing the structural geometry of the growing hair root and the surrounding follicular sheath without disrupting essential developmental processes.
Hair Texture and Genome-Wide Research
Scalp hair morphology—ranging from straight to wavy, curly, and tightly coiled—is a polygenic trait governed by multiple loci acting in concert across the human genome. Population geneticists performing genome-wide association studies (GWAS) have repeatedly evaluated self-reported and objectively graded hair curliness across thousands of individuals. In these population cohorts, rs11603555 emerged with moderate statistical evidence as a marker linked to shifts in hair curliness, alongside major structural genes such as TCHH (trichohyalin) and EDAR. While structural proteins directly compose the hair shaft, regulatory loci such as rs11603555 are hypothesized to act by fine-tuning signaling cascades during the development of follicular asymmetry, which physically directs whether a hair fiber grows round and straight or elliptical and curved.
Strength of Scientific Evidence and Biological Complexities
The association between rs11603555 and hair curliness carries moderate statistical support in published genomics catalogs. Like most common traits, hair shape is not determined by an isolated genetic switch. Instead, individual loci account for modest shifts in the odds of having wavy or curly hair versus straight hair. Furthermore, hair curvature is influenced by multi-locus gene-gene interactions, sex hormone levels, aging, and external grooming treatments. Because genome-wide association studies examine statistical correlation rather than direct physical causation, rs11603555 may itself alter regulatory binding or may exist in strong linkage disequilibrium with another nearby causal functional variant. Additional fine-mapping and molecular biology analyses are continuously refining our precise mechanistic understanding of this locus.
Population Patterns and Ancestry Considerations
The frequency of rs11603555 alleles exhibits notable variation across geographic ancestral groups. In populations of European descent, the minor allele frequency is approximately 0.28, rendering both the common and alternate alleles widespread throughout the general public. In contrast, East Asian and African populations show markedly different allele frequency landscapes and genetic architectures governing hair morphology; for example, the EDAR gene plays a predominant role in hair thickness and straightness in East Asian ancestries. Consequently, the predictive strength of rs11603555 observed in European cohorts does not automatically transfer with identical effect sizes across all ancestral backgrounds, highlighting the importance of evaluating genetic markers within an ancestry-specific scientific context.
What You Can and Cannot Do with This Information
Knowledge of your rs11603555 genotype serves solely as an intriguing glimpse into human physical diversity and consumer polygenic architecture. This variant is completely benign and does not confer risk for congenital hair disorders, alopecia, or systemic illness. Consumers should not use single-locus findings to predict a child's exact hair type or attempt to reverse natural hair texture changes. Because hair care regimens, styling tools, chemical treatments, and humidity interact with hair proteins on a physical level, your lived daily experience with your hair depends on structural hair health rather than any individual DNA marker. This genetic insight should simply be appreciated as an educational showcase of human genetic variation.
How common is this variant?
The minor allele frequency for rs11603555 is approximately 0.28 in populations of European ancestry, meaning both alleles are widely represented. Frequencies vary considerably across other global populations, reflecting distinct regional genetic architectures for physical traits.
Frequently asked questions
Does rs11603555 determine whether my hair is straight or curly?
No, a single genetic variant cannot entirely determine your hair texture. Scalp hair shape is polygenic, meaning dozens of variants across genes such as TCHH, EDAR, and ASCL1 contribute small incremental effects to the curvature of the follicle.
Is the rs11603555 variant related to any hair loss disorders?
There is no clinical evidence linking rs11603555 to alopecia, balding, or pathological hair loss syndromes. It is categorized strictly as a normal trait-associated marker affecting physical hair fiber morphology.
Can external factors change my genetic hair texture?
While your underlying DNA sequence remains unchanged throughout life, external factors such as chemical relaxers, heat styling, hormonal fluctuations, and aging can alter the physical shape and curl pattern of your hair strands.
Does rs11603555 have the same effect across all ancestries?
Not necessarily. Most studies demonstrating this association were conducted in individuals of European ancestry; different populations often possess unique genetic variants and background allele frequencies that govern hair texture.
Sources & further reading
Educational information only, last refreshed 9/5/2026. Not medical advice — these associations describe population statistics, not individual predictions.
Curious what your genotype is for rs11603555?
Upload a raw DNA file from 23andMe, AncestryDNA, MyHeritage, or FamilyTreeDNA and see this variant — plus thousands more — interpreted in your full report.
Get my report — $29