Chromomere

Definition

A locally condensed, bead-like granule of chromatin visible along a eukaryotic chromosome during prophase of mitosis and meiosis, formed by localized coiling and compaction of DNA-protein complexes in transcriptionally inactive regions. In standard chromosomes, chromomeres appear as serially aligned granules; in polytene chromosomes, they aggregate to form the dark, transcriptionally inactive bands (interbands represent the lighter, more extended regions).

Etymology

Greek chroma (color) + meros (part), referring to the stained, particulate appearance of condensed chromatin.

Example

In Drosophila melanogaster salivary gland polytene chromosomes, the distinctive banding pattern of alternating dark chromomeres and light interbands allows cytogeneticists to map gene locations and identify chromosomal rearrangements such as inversions and translocations used in population genetics and species diagnostics.

Synonyms

• idiomere

Related Terms

• chromatin
• polytene chromosome
• chromonema
• chromatid
• interband
• endomitosis
• karyotype
• puff (chromosomal)

Usage Notes

Chromomere and chromomere-derived band are sometimes used interchangeably in polytene chromosome literature, but strictly, chromomeres are the underlying condensed units while bands are the visible cytological result. The term contrasts with chromonema, the extended, thread-like core of the chromosome. In arthropod cytogenetics, chromomere patterns are especially important for dipteran and chironomid identification, where species-specific banding sequences serve as diagnostic characters.