Evolutionary trajectories of three independent neo-sex chromosomes in <i>Drosophila</i>
Bibliographic record
Abstract
ABSTRACT Dosage compensation (DC) on the X chromosome is a mechanism to counteract the deleterious effects by gene loss from the Y chromosome. However, DC cannot work efficiently if the X chromosome also degenerates. This indeed occurs in the neo-sex chromosomes in Drosophila miranda , where neo-X as well as neo-Y chromosomes are under accelerated pseudogenization. To examine the generality of this pattern, we investigated the evolution of two additional neo-sex chromosomes that independently emerged in D. albomicans and D. americana and compared their evolutionary processes with that in D. miranda . Comparative genomic and transcriptomic analyses revealed that the pseudogenization rate on neo-X is also accelerated in the two species (though lesser extent in D. americana ). We also found that neo-X-linked genes whose neo-Y homologs are pseudogenized tend to be upregulated more stringently than those whose neo-Y homologs remain functional. Moreover, the genes under strong functional constraints and highly expressed in the testis tended to remain functional on neo-X and neo-Y, respectively. Focusing on the D. miranda and D. albomicans neo-sex chromosomes that independently emerged from the same autosome, we further found that the same genes tend to have been pseudogenized in parallel on neo-Y. Those genes include Idgf6 and JhI-26 whose functions seem to be unnecessary or could be even harmful for males. These results indicate that neo-sex chromosomes in Drosophila share a common evolutionary trajectory after their emergence, which may be applicable to other sex chromosomes in a variety of organisms to avoid being an evolutionary dead-end.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".