C1C4

C1C4 is a designation used in different fields to denote distinct concepts. Because it spans biology, chemistry, and other technical domains, there is no single, universal definition. In each context, C1C4 carries a specific meaning linked to a range or cluster of related elements.

In human genetics, C1-C4 has appeared as a shorthand related to the major histocompatibility complex (MHC) class III region. This segment, located on chromosome 6 in some labeling schemes, includes several immune-related genes such as those encoding components of the complement system. Modern references typically name the individual genes (for example, C2 and C4A/C4B) rather than a continuous C1-C4 block. Variation in copy number for C4A and C4B is associated with differences in immune function and with susceptibilities to autoimmune diseases in some populations. The exact boundaries and gene content of what was called the C1-C4 region can vary by annotation.

In petrochemical and analytical contexts, C1-C4 refers to the light end of the hydrocarbon spectrum, comprising compounds with one to four carbon atoms, such as methane (C1), ethane (C2), propane (C3), and butane (C4). This range is used to describe feedstocks, gas streams, or fractions in refining and is common in gas chromatography reporting.

The term may also appear as a project, model, or route code in various technical disciplines. Absent domain context, C1C4 is ambiguous, and the intended meaning should be inferred from accompanying documentation or data.