Dysploidy
One-sentence definition. Dysploidy is a change in chromosome number by one or a small number of whole chromosomes through fusion (reducing count) or fission (increasing count) — as opposed to polyploidy, which multiplies the entire genome.
One-sentence analogy. Dysploidy is like dividing a bookshelf by pulling one book off and splitting it into two thin volumes (fission) or gluing two thin books together (fusion) — the library changes in unit count, but you have roughly the same total text.
Why it matters. Dysploidy is the most common mode of karyotype evolution in animals and is strongly influenced by effective population size. In Carnivora, lineages with small geographic ranges (a proxy for low Ne) show higher rates of both fusions and fissions than large-range lineages, with credible intervals entirely above zero. This pattern supports drift-based models of chromosome evolution: small populations fix slightly deleterious rearrangements more readily. Dysploidy through sex-chromosome–autosome fusions also produces neo-sex chromosomes.
Where you meet it in the wiki.
- Chromosome number evolution — rates of fission and fusion across taxa.
- Karyotype evolution overview — drift vs. selection in chromosome number change.
Primary citation.
“We found a ΔR fusion of 0.101 (CI 0.062 to 0.141) and a ΔR fission of 0.163 (CI 0.116 to 0.207).” — Jonika et al. 2024, Finding 1
Prerequisites: autosome, aneuploidy Next, learn about: robertsonian translocation, chromosome fusion