Neo-Sex Chromosome
One-sentence definition. A neo-sex chromosome is a newly derived sex chromosome formed when an autosome fuses with, or is recruited as a replacement for, an existing sex chromosome — starting a fresh cycle of sex chromosome evolution.
One-sentence analogy. A neo-sex chromosome is like a newly hired employee placed in a specialized department: once there, they quickly acquire the specialized characteristics (and limitations) of that department, often losing skills they had in the general workforce.
Why it matters. Neo-sex chromosomes reveal the speed of sex chromosome evolution. In Drosophila miranda, a neo-Y formed by a Y–autosome fusion ~1–2 million years ago has already lost or pseudogenized 40% of its ancestral autosomal genes and accumulated transposable elements — demonstrating that Y degeneration proceeds rapidly. Neo-X chromosomes in threespine sticklebacks accumulate loci for behavioral reproductive isolation even before hybrid sterility loci appear, showing that neo-sex chromosomes can drive speciation.
Where you meet it in the wiki.
- Sex chromosome evolution — neo-sex chromosomes illustrate the pace of Y degeneration.
- Y-naught asymmetry — neo-Y degeneration rate benchmarks.
- Hybrid sterility — chromosome age shapes which barriers accumulate on sex chromosomes.
Primary citation.
“In D. miranda the neo-Y, which formed by a Y to autosome fusion approximately 1–2 million years ago, has already accumulated a large number of transposable elements and 40% of the ancestral autosomal genes have been pseudogenized or lost.” — Blackmon & Demuth 2015, Finding 2
Prerequisites: heterogamety, autosome, chromosome fusion Next, learn about: recombination suppression, SA fusion