Breadcrumb Home Glossary of Terms and Abbreviations - L A / B / C / D / E / F / G / H / I / J / K / L / M / N / O / P / Q / R / S / T / U / V / W / X / YLocus (pl. loci):A specific position of a gene or DNA marker on a chromosome.Locus heterogeneity:Genes at different chromosomal positions (loci) result in the same phenotype.Loss-of-function mutation (LOF):A DNA alteration which results in reduced or abolished protein activity.