Ancient gene duplicates in Gossypium (cotton) exhibit near-complete expression divergence.
The main results reproduced, with only marginal, non-material deviations.
A 0–100 reproducibility-quality score from the per-question grades, shown as a z-score: standard deviations above (+) or below (−) the mean of comparable assessments.
▸Reproduction agent’s raw note
Reproduced two of the paper's core pipeline steps end-to-end on one representative RNA-seq library (SRX172483/SRR530667, G. hirsutum leaf): sickle v1.33 quality trimming (8,158,340 -> 8,019,202 reads) and GMAP-GSNAP splice-aware alignment to the G. raimondii reference genome (94.86% of alignment records / 92.6% of reads mapped). Went beyond the minimum by also computing an approximate, single-genome (non-homoeolog-resolved) gene-level read count and RPKM table (30,003/38,208 genes with nonzero counts, 92.66% of mapped reads assigned to gene bodies) as a partial, honestly-scoped stand-in for the paper's full homoeolog-resolved RPKM/UQ + t-test/GLM differential-expression analysis, whichrequires infrastructure (dual A/D-genome homoeolog SNP-sorting, R-based GLM with edgeR-style negative binomial, 22 additional SRA accessions across leaf/seed/petal tissues) not established in this environment and was not attempted rather than faked. The paper itself publishes no per-accession numeric QC statistics (trim counts, mapping rates) to compare against, so all three claims are graded 'partial': the pipeline steps are verified to run correctly and produce internally consistent, biologically plausible numbers, but cannot be graded exact/within-tolerance/mismatch against a published number that does not exist. Only one of 23 total SRA accessions referenced by the paper was profiled in this run; the other 22 (SRX172484-SRX172485, SRX170955, SRX172454, SRX172473, SRX204399-SRX204401, SRX204405-SRX204407, SRX204429-SRX204434, SRX204555-SRX204558, SRX328344) were not downloaded or profiled due to scope/time, and this is an explicit, documented limitation rather than a claim of completeness.
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- 2026-08-03
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- Last updated
- 2026-08-05
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Deep full-text extraction
Model: opusWhat evolutionary processes maintain gene duplicates over long time scales following ancient whole genome duplication? The authors test whether paralogs retained from the ~60 My old Gossypium-specific 5- to 6-fold ploidy increase have undergone expression-level neo- and/or subfunctionalization.
- ★ Nearly all (99.4%) ancient paralog pairs in Gossypium raimondii are differentially expressed in at least one of three tissues (petal, leaf, seed), indicating massive, near-complete expression-level divergence. finding
- ★ A generalized linear model showed 92.4% of paralog pairs exhibit expression divergence, with most showing significant gene-by-tissue interactions indicating complementary expression across tissues. finding
- ★ Expression divergence is mirrored in G. arboreum and in a G. raimondii seed developmental time series, indicating expression-level diversification occurred before species divergence in the common ancestor. finding
- ★ Expression-level neo- and/or subfunctionalization is essential to the maintenance of these duplicates over ~60 My. mechanism
- ★ 1,971 strictly duplicated paralogous gene pairs were identified in G. raimondii, traceable to the Gossypium-specific whole genome multiplication. resource
- ★ Strictly duplicated genes can be identified by requiring duplicate syntenic regions in G. raimondii that correspond to only a single genomic region in both Theobroma cacao and Vitis vinifera, thereby excluding the older shared eudicot triplication. method
- Retained duplicate genes are broadly distributed across chromosomes without positional bias, apart from being densest in regions of high overall gene density such as subtelomeric regions. finding
- Paralogs at a given chromosomal region are not more likely to be over- or underexpressed relative to their counterpart, i.e., no positional (subgenome-like) expression bias was detected. finding
| Assay | System | Perturbation | Readout | Platform |
|---|---|---|---|---|
| Comparative genomics / synteny and sequence-similarity analysis | Gossypium raimondii genome vs Theobroma cacao and Vitis vinifera genomes | none | Identification of strictly duplicated paralogous gene pairs (duplicated syntenic regions in G. raimondii mapping to a single region in T. cacao and V. vinifera) | — |
| Coding sequence alignment and dN/dS estimation | Primary transcripts of paralogous gene pairs in G. raimondii | none | dN/dS ratios per paralog pair | ClustalW; custom BioPerl scripts; Jukes-Cantor substitution model |
| Bulk RNA-seq (differential expression between paralogs) | Gossypium raimondii leaf, petal, and seed (10 DPA) tissue; three biological replicates per tissue | none | Uniquely mapped read coverage over ~37,000 gene annotations, RPKM and upper-quartile normalized; log ratio of paralog expression | Public NCBI SRA data (SRX172483-SRX172485, SRX204399-SRX204401, SRX204405-SRX204407, SRX204429-SRX204434, SRX328344); sickle QC; GSNAP mapping; samtools |
| Bulk RNA-seq (differential expression between paralogs) | Gossypium arboreum leaf, petal, and seed; three biological replicates per tissue | none | Uniquely mapped read coverage and paralog expression log ratios, reads mapped to G. raimondii genome using a Gossypium-specific SNP index to reduce mapping bias | NCBI SRA (SRX170955, SRX172454, SRX172473, SRX204555-SRX204558, SRX328344); GSNAP; Gossypium SNP index |
| Bulk RNA-seq developmental time series | Gossypium raimondii seed, 10-40 DPA | none (developmental stage series) | Differential expression between paralogs across developmental stages | — |
| Generalized linear model (negative binomial) with contrasts | UQ-normalized RNA-seq counts from G. raimondii petal, seed, and leaf | none | Gene effect, tissue effect, gene-by-tissue interaction, per-tissue differential expression (G|T), and complementary expression patterns; FDR 5% (Benjamini-Hochberg) | R (contrasts package) |
| Tissue-specific reciprocal silencing analysis | Differentially expressed paralog pairs of G. raimondii and G. arboreum across tissues/time points | none | Cases where one paralog accounts for >=95% of the pair's total RPKM and the bias is reversed in one or more tissues/time points | — |
| Genomic distribution / positional bias analysis | G. raimondii chromosome scaffolds; leaf, seed, and petal expression data | none | Circos visualization of paralog positions and gene density; binomial test for regional over- or underexpression bias, FDR 5% | Circos |
- – 99.4% of paralog pairs in G. raimondii are differentially expressed in at least one of petal, leaf, or seed; 93-94% per tissue 99.4%
- – 1,666 (85%) of pairs are differentially expressed in all three tissues; 88-89% in two of three tissues 1,666 pairs (85%)
- – In G. arboreum, 1,962 (99.5%) paralogs show transcriptional divergence in at least one tissue; 92-95% per tissue and 86-88% in at least two tissues 1,962/1,971 (99.5%)
- – GLM revealed 92.4% of paralog pairs exhibit expression divergence, most with significant gene and tissue interaction effects 92.4%
- – All but two paralog pairs (1,969 of 1,971) were differentially expressed in both species in at least one tissue; 87% and 90% in petal and leaf respectively in both species; 74% divergent in all tissues of both species 1,969/1,971; 74%
- – In a G. raimondii seed developmental time series (10-40 DPA), 1,961 (99.5%) paralogs were differentially expressed in at least one developmental stage 1,961 (99.5%)
- – 1,809 of 1,971 G. raimondii pairs (and 1,811 in G. arboreum) show significant and substantial (>=1.5-fold) divergence in at least one tissue; in all tissues of both species at least 25% of paralogs differ by at least 5-fold >=1.5-fold in 1,809/1,971; >=5-fold in >=25%
- – No significant departure from expectation for regional over- or underexpression bias in leaf, seed, or petal after FDR correction
- count 1,971 strictly duplicated paralogous gene pairs (Paralogs identified in G. raimondii from the Gossypium-specific 5- to 6-fold ploidy increase)
- other 99.4% (Percent of G. raimondii paralog pairs differentially expressed in at least one of three tissues)
- count 1,666 (85%) (Pairs differentially expressed in all three tissues (petal, leaf, seed) in G. raimondii)
- other 92.4% (Paralog pairs with expression divergence by the negative binomial GLM)
- count 1,962 (99.5%) (G. arboreum paralogs with transcriptional divergence in at least one tissue)
- fold_change Petal 1,462 / 1,237 / 715 pairs at >=1.5-, 2-, 5-fold; Leaf 1,380 / 1,076 / 496; Seed 1,379 / 1,119 / 551; max in any tissue 1,809 / 1,644 / 1,026 (G. raimondii) (Table 1 fold-change distribution in G. raimondii tissues)
- fold_change Petal 1,481 / 1,259 / 742; Leaf 1,403 / 1,087 / 508; Seed 1,409 / 1,134 / 568; max in any tissue 1,811 / 1,645 / 1,027 (G. arboreum) (Table 1 fold-change distribution in G. arboreum tissues)
- count 1,825 pairs differentially expressed in petal, 1,746 of which are also differentially expressed in seed (10 DPA); 1,278 pairs biased in the same direction in petal and seed (Figure 2A tissue overlap in G. raimondii)
Statistical methods review
Model: sonnetA neutral, descriptive read of the statistical approach — what was done, and (for shared learning, not as criticism) what could also have been done.
The paper compares RNA-seq-derived expression levels between ~2,000 pairs of ancient paralogous genes in two Gossypium species across three tissues (and a seed developmental time series), using three biological replicates per tissue/time point. Differential expression between paralogs was assessed with Student's t-tests on log ratios of normalized expression (RPKM and, separately, upper-quartile normalization), with results corrected for a 5% false discovery rate. A generalized linear model (negative binomial, fit in R) was additionally used to partition gene, tissue, and gene-by-tissue interaction effects, and a Wilcoxon signed-rank test compared dN/dS ratios between resulting gene groups; results were reported primarily as counts and percentages of paralog pairs meeting significance and fold-change thresholds.
| Test | Applied to | n | Assumptions |
|---|---|---|---|
| Student's t-test on log ratio of paralog expression (RPKM-normalized, and separately UQ-normalized) | differential expression between paralogous gene pairs within and between tissues/time points, G. raimondii and G. arboreum | three biological replicates per tissue/time point | stated |
| Generalized linear model, negative binomial distribution (R, contrasts package) | gene (G), tissue (T), and gene-by-tissue (G×T) interaction effects, and per-tissue (G|T) contrasts, on UQ-normalized RNA-seq data in petal, seed, and leaf of G. raimondii | three biological replicates per tissue | not stated |
| Binomial test | whether paralogs at a given chromosomal position were more often over- or underexpressed relative to their duplicate counterpart | — | not stated |
| Wilcoxon signed-rank test | comparison of mean dN/dS ratios between paralog groups defined by G, T, and G×T effect patterns | — | not stated |
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Differential expression between paralogs was assessed with Student's t-tests on log ratios of RPKM/UQ-normalized values, with normality checked by visual inspection of the log-ratio distribution.↳ Could also: RNA-seq-specific count-based frameworks such as DESeq2 or edgeR, which model raw counts with a negative binomial distribution and shrink dispersion estimates across genes — these tools are built to handle the mean-variance structure and overdispersion typical of RNA-seq counts directly, which can be useful with a small number of replicates, without relying on log-ratio normality.
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Gene, tissue, and gene-by-tissue interaction effects were estimated with a negative binomial GLM implemented in base R.↳ Could also: established RNA-seq differential expression packages (e.g., edgeR glmQLFit, DESeq2 likelihood ratio test) that implement similar negative-binomial GLM frameworks with additional empirical Bayes dispersion shrinkage — dispersion shrinkage across genes can stabilize variance estimates and improve power when replicate numbers are limited.
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Multiple testing was controlled using the Benjamini-Hochberg FDR procedure at a 5% threshold, applied separately within each test family.↳ Could also: Storey's q-value approach, which adaptively estimates the proportion of true null hypotheses — q-value methods can offer somewhat greater power than the standard BH step-up procedure while still controlling the false discovery rate, particularly when many hypotheses are truly non-null.
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Differential expression between paralog pairs was evaluated using a t-test on the log ratio, treating each paralog pair as a matched comparison.↳ Could also: a paired nonparametric alternative such as the Wilcoxon signed-rank test on the same log ratios — a rank-based paired test avoids reliance on the log-ratio data approximating a normal distribution and can be a natural complement when normality is inspected only visually.
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Differences in dN/dS ratios among paralog groups (defined by significant G, T, and G×T effects) were tested with a single Wilcoxon signed-rank test.↳ Could also: a Kruskal-Wallis test (with post-hoc pairwise comparisons) when more than two groups are being compared — Kruskal-Wallis extends the same nonparametric rank-based logic to simultaneous comparison of multiple groups while controlling the overall test-wise error rate across the group set.
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Replicate numbers (three biological replicates per tissue/time point) were used without describing a formal power calculation.↳ Could also: an a priori power analysis based on expected RNA-seq count variance to justify replicate number — explicit power calculations can help communicate the expected sensitivity to detect a given fold-change in expression given the chosen replicate depth.
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