Holocentric Chromosome

One-sentence definition. A holocentric chromosome has centromere activity distributed along its entire length rather than restricted to a single point, so spindle fibers can attach anywhere along the chromosome during cell division.

One-sentence analogy. In a monocentric chromosome the spindle hooks onto one specific handle; in a holocentric chromosome the entire surface is covered in handles — any spindle fiber can grab anywhere, making the chromosome more tolerant of fragmentation and fission events.

Why it matters. Holocentricity fundamentally changes the consequences of chromosome rearrangements. In monocentric chromosomes, fission produces an acentric fragment that is lost; in holocentric chromosomes, fission produces two viable daughter chromosomes (because both fragments retain centromere activity). This may explain why lineages with holocentric chromosomes — notably many Lepidoptera and Hemiptera — tolerate higher rates of chromosome number change via fission. Phylogenetic model comparison has found a trend (83% posterior above zero) toward higher fission rates in holocentric lineages, though with wide credible intervals. Importantly, holocentric and monocentric lineages show higher microsatellite evolution rates in monocentric taxa despite similar overall microsatellite content.

Where you meet it in the wiki.

• Holocentric chromosomes — detailed discussion of genomic consequences.
• Chromosome number evolution — whether holocentricity elevates fission rates.

Primary citation. null

Prerequisites: autosome Next, learn about: achiasmy, dysploidy