What this means

CLOCK is one of the core transcription factors in the molecular circadian oscillator that keeps every cell's rhythm in step. The T3111C variant (rs1801260) sits in the 3' untranslated region and subtly alters how the CLOCK transcript is regulated. Studies link the C allele to a small shift toward eveningness and slightly later sleep timing. Chronotype is highly heritable overall (around 40–50%) but hundreds of genes contribute — a single SNP shifts you a notch, not a category.

CLOCK is one of a handful of core genes that keep your body's daily rhythm running — the 24-hour cycle that sets when you naturally feel sleepy or alert. A common DNA change in this gene subtly tweaks how it gets regulated, and studies link one version to a small shift toward being more of a night owl. Whether you're a morning person or an evening person is roughly 40–50% genetic overall, but it involves hundreds of genes — this one SNP nudges you a notch, not a category.

Caveats

• Single-SNP effects on chronotype are very small; polygenic scores do better.
• Chronotype changes naturally across life — most teenagers shift later, most retirees shift earlier.
• Sunlight, screen time, and work schedule shape sleep timing more than this gene.
• Not all morning/evening preference studies have reproduced this association cleanly.

References

• Katzenberg et al. — A CLOCK polymorphism associated with human diurnal preference (Sleep, 1998)
• Jones et al. — Genome-wide association analyses of chronotype in 697,828 individuals provides insights into circadian rhythms (Nature Communications, 2019)