Novel genetic variants of the Period (Drosophila) Homolog 1 (PER1) gene are described. Various genotypes, haplotypes, and haplotype pairs that exist in the general United States population are disclosed for the PER1 gene. Compositions and methods for haplotyping and/or genotyping the PER1 gene in an individual are also disclosed. Polynucleotides defined by the haplotypes disclosed herein are also described.
