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The Florida Scrub-Jay (Aphelocoma coerulescens), a Federally Threatened, cooperatively-breeding bird, is an emerging model system in evolutionary biology and ecology. Extensive individual-based monitoring and genetic sampling for decades has yielded a wealth of data, allowing for the detailed study of social behavior, demography, and population genetics of this natural population. Here, we report a linkage map and a chromosome-level genome assembly and annotation for a female Florida Scrub-Jay made with long-read sequencing technology, chromatin conformation data, and the linkage map. We constructed a linkage map comprising 4,468 SNPs that had 34 linkage groups and a total sex-averaged autosomal genetic map length of 2446.78 cM. The new genome assembly is 1.33 Gb in length, consisting of 33 complete or near-complete autosomes and the sex chromosomes (ZW). This highly contiguous assembly has an NG50 of 68 Mb and a Benchmarking Universal Single-Copy Orthologs (BUSCO) completeness score of 97.1% with respect to the Aves database. The annotated gene set has a BUSCO transcriptome completeness score of 95.5% and 17,964 identified protein-coding genes, 92.5% of which have associated functional annotations. This new, high-quality genome assembly and linkage map of the Florida Scrub-Jay provides valuable tools for future research into the evolutionary dynamics of small, natural populations of conservation concern., (© The Author(s) 2024. Published by Oxford University Press on behalf of The Genetics Society of America.)

Currently available genome assemblies for Atlantic cod (Gadus morhua) have been constructed from fish belonging to the Northeast Arctic Cod (NEAC) population; a migratory population feeding in the Barents Sea. These assemblies have been crucial for the development of genetic markers which have been used to study population differentiation and adaptive evolution in Atlantic cod, pinpointing four discrete islands of genomic divergence located on linkage groups 1, 2, 7 and 12. In this paper, we present a high-quality reference genome from a male Atlantic cod representing a southern population inhabiting the Celtic sea. The genome assembly (gadMor_Celtic) was produced from long-read nanopore data and has a combined contig length of 686 Mb with an N50 of 10 Mb. Integrating contigs with genetic linkage mapping information enabled us to construct 23 chromosome sequences which mapped with high confidence to the latest NEAC population assembly (gadMor3) and allowed us to characterize, to an extent not previously reported large chromosomal inversions on linkage groups 1, 2, 7 and 12. In most cases, inversion breakpoints could be located within single nanopore contigs. Our results suggest the presence of inversions in Celtic cod on linkage groups 6, 11 and 21, although these remain to be confirmed. Further, we identified a specific repetitive element that is relatively enriched at predicted centromeric regions. Our gadMor_Celtic assembly provides a resource representing a ‘southern’ cod population which is complementary to the existing ‘northern’ population based genome assemblies and represents the first step toward developing pan-genomic resources for Atlantic cod.

Although seed and pod traits are important for peanut breeding, little is known about the inheritance of these traits. A recombinant inbred line (RIL) population of 156 lines from a cross of Tifrunner x NC 3033 was genotyped with the Axiom_Arachis1 SNP array and SSRs to generate a genetic map composed of 1524 markers in 29 linkage groups (LG). The genetic positions of markers were compared with their physical positions on the peanut genome to confirm the validity of the linkage map and explore the distribution of recombination and potential chromosomal rearrangements. This linkage map was then used to identify Quantitative Trait Loci (QTL) for seed and pod traits that were phenotyped over three consecutive years for the purpose of developing trait-associated markers for breeding. Forty-nine QTL were identified in 14 LG for seed size index, kernel percentage, seed weight, pod weight, single-kernel, double-kernel, pod area and pod density. Twenty QTL demonstrated phenotypic variance explained (PVE) greater than 10% and eight more than 20%. Of note, seven of the eight major QTL for pod area, pod weight and seed weight (PVE >20% variance) were attributed to NC 3033 and located in a single linkage group, LG B06_1. In contrast, the most consistent QTL for kernel percentage were located on A07/B07 and derived from Tifrunner.

Understanding the genomic basis of adaptative intraspecific phenotypic variation is a central goal in conservation genetics and evolutionary biology. Lake trout (Salvelinus namaycush) are an excellent species for addressing the genetic basis for adaptive variation because they express a striking degree of ecophenotypic variation across their range; however, necessary genomic resources are lacking. Here we utilize recently-developed analytical methods and sequencing technologies to (1) construct a high-density linkage and centromere map for lake trout, (2) identify loci underlying variation in traits that differentiate lake trout ecophenotypes and populations, (3) determine the location of the lake trout sex determination locus, and (4) identify chromosomal homologies between lake trout and other salmonids of varying divergence. The resulting linkage map contains 15,740 single nucleotide polymorphisms (SNPs) mapped to 42 linkage groups, likely representing the 42 lake trout chromosomes. Female and male linkage group lengths ranged from 43.07 to 134.64 centimorgans, and 1.97 to 92.87 centimorgans, respectively. We improved the map by determining coordinates for 41 of 42 centromeres, resulting in a map with 8 metacentric chromosomes and 34 acrocentric or telocentric chromosomes. We use the map to localize the sex determination locus and multiple quantitative trait loci (QTL) associated with intraspecific phenotypic divergence including traits related to growth and body condition, patterns of skin pigmentation, and two composite geomorphometric variables quantifying body shape. Two QTL for the presence of vermiculations and spots mapped with high certainty to an arm of linkage group Sna3, growth related traits mapped to two QTL on linkage groups Sna1 and Sna12, and putative body shape QTL were detected on six separate linkage groups. The sex determination locus was mapped to Sna4 with high confidence. Synteny analysis revealed that lake trout and congener Arctic char (Salvelinus alpinus) are likely differentiated by three or four chromosomal fissions, possibly one chromosomal fusion, and 6 or more large inversions. Combining centromere mapping information with putative inversion coordinates revealed that the majority of detected inversions differentiating lake trout from other salmonids are pericentric and located on acrocentric and telocentric linkage groups. Our results suggest that speciation and adaptive divergence within the genus Salvelinus may have been associated with multiple pericentric inversions occurring primarily on acrocentric and telocentric chromosomes. The linkage map presented here will be a critical resource for advancing conservation oriented genomic research on lake trout and exploring chromosomal evolution within and between salmonid species.

The rate of meiotic recombination is one of the central factors determining genome-wide levels of linkage disequilibrium which has important consequences for the efficiency of natural selection and for the dissection of quantitative traits. Here we present a new, high-resolution linkage map for Populus tremula that we use to anchor approximately two thirds of the P. tremula draft genome assembly on to the expected 19 chromosomes, providing us with the first chromosome-scale assembly for P. tremula (Table 2). We then use this resource to estimate variation in recombination rates across the P. tremula genome and compare these results to recombination rates based on linkage disequilibrium in a large number of unrelated individuals. We also assess how variation in recombination rates is associated with a number of genomic features, such as gene density, repeat density and methylation levels. We find that recombination rates obtained from the two methods largely agree, although the LD-based method identifies a number of genomic regions with very high recombination rates that the map-based method fails to detect. Linkage map and LD-based estimates of recombination rates are positively correlated and show similar correlations with other genomic features, showing that both methods can accurately infer recombination rate variation across the genome. Recombination rates are positively correlated with gene density and negatively correlated with repeat density and methylation levels, suggesting that recombination is largely directed toward gene regions in P. tremula.

Platycladus orientalis is an ecologically important native conifer in Northern China and exotic species in many parts of the world; however, knowledge about the species’ genetics and genome are very limited. The availability of well-developed battery of genetic markers, with large genome coverage, is a prerequisite for the species genetic dissection of adaptive attributes and efficient selective breeding. Here, we present a genome-wide genotyping method with double-digestion restriction site associated DNA sequencing (ddRAD-seq) that is effective in generating large number of Mendelian markers for genome mapping and other genetic applications. Using 139 megagametophytes collected from a single mother tree, we assembled 397,226 loci, of which 108,683 (27.4%) were polymorphic. After stringent filtering for 1:1 segregation ratio and missing rate of

Medaka (Oryzias sp.) is an important fish species in ecotoxicology and considered as a model species due to its biological features including small body size and short generation time. Since Japanese medaka Oryzias latipes is a freshwater species with access to an excellent genome resource, the marine medaka Oryzias melastigma is also applicable for the marine ecotoxicology. In genome era, a high-density genetic linkage map is a very useful resource in genomic research, providing a means for comparative genomic analysis and verification of de novo genome assembly. In this study, we developed a high-density genetic linkage map for O. melastigma using restriction-site associated DNA sequencing (RAD-seq). The genetic map consisted of 24 linkage groups with 2,481 single nucleotide polymorphism (SNP) markers. The total map length was 1,784 cM with an average marker space of 0.72 cM. The genetic map was integrated with the reference-assisted chromosome assembly (RACA) of O. melastigma, which anchored 90.7% of the assembled sequence onto the linkage map. The values of complete Benchmarking Universal Single-Copy Orthologs were similar to RACA assembly but N50 (23.74 Mb; total genome length 779.4 Mb; gap 5.29%) increased to 29.99 Mb (total genome length 778.7 Mb; gap 5.2%). Using MapQTL analysis with SNP markers, we identified a major quantitative trait locus for sex traits on the Om10. The integration of the genetic map with the reference genome of marine medaka will serve as a good resource for studies in molecular toxicology, genomics, CRISPR/Cas9, and epigenetics.

Characterizing the genetic variation underlying phenotypic traits is a central objective in biological research. This research has been hampered in the past by the limited genomic resources available for most non-model species. However, recent advances in sequencing technologies and related genotyping methods are rapidly changing this. Here we report the use of genome-wide SNP data from the ecologically and commercially important marine fish species Chrysophrys auratus (snapper) to 1) construct the first linkage map for this species, 2) scan for growth QTL, and 3) search for putative candidate genes in the surrounding QTL regions. The newly constructed linkage map contained ∼11K SNP markers and is one of the densest maps to date in the fish family Sparidae. Comparisons with genome scaffolds of the recently assembled snapper genome indicated that marker placement was mostly consistent between the scaffolds and linkage map (R = 0.7), but that at fine scales (< 5 cM) some precision limitations occurred. Of the 24 linkage groups, which likely reflect the 24 chromosomes of this species, three were found to contain QTL with genome-wide significance for growth-related traits. A scan of 13 candidate growth genes located the growth hormone, myogenin, and parvalbumin genes within 5.3, 9.6, and 25.0 cM of these QTL, respectively. The linkage map and QTL found in this study will advance the investigation of genome structure and aquaculture breeding efforts in this and related species.

High-density linkage maps are an important tool to gain insight into the genetic architecture of traits of evolutionary and economic interest, and provide a resource to characterize variation in recombination landscapes. Here, we used information from the cattle genome and the 50 K Cervine Illumina BeadChip to inform and refine a high-density linkage map in a wild population of red deer (Cervus elaphus). We constructed a predicted linkage map of 38,038 SNPs and a skeleton map of 10,835 SNPs across 34 linkage groups. We identified several chromosomal rearrangements in the deer lineage relative to sheep and cattle, including six chromosome fissions, one fusion, and two large inversions. Otherwise, our findings showed strong concordance with map orders in the cattle genome. The sex-averaged linkage map length was 2739.7 cM and the genome-wide autosomal recombination rate was 1.04 cM/Mb. The female autosomal map length was 1.21 longer than that of males (2767.4 cM vs. 2280.8 cM, respectively). Sex differences in map length were driven by high female recombination rates in peri-centromeric regions, a pattern that is unusual relative to other mammal species. This effect was more pronounced in fission chromosomes that would have had to produce new centromeres. We propose two hypotheses to explain this effect: (1) that this mechanism may have evolved to counteract centromeric drive associated with meiotic asymmetry in oocyte production; and/or (2) that sequence and structural characteristics suppressing recombination in close proximity to the centromere may not have evolved at neo-centromeres. Our study provides insight into how recombination landscapes vary and evolve in mammals, and will provide a valuable resource for studies of evolution, genetic improvement, and population management in red deer and related species.

The aquatic planorbid snail Biomphalaria glabrata is one of the most intensively-studied mollusks due to its role in the transmission of schistosomiasis. Its 916 Mb genome has recently been sequenced and annotated, but it remains poorly assembled. Here, we used targeted capture markers to map over 10,000 B. glabrata scaffolds in a linkage cross of 94 F1 offspring, generating 24 linkage groups (LGs). We added additional scaffolds to these LGs based on linkage disequilibrium (LD) analysis of targeted capture and whole-genome sequences of 96 unrelated snails. Our final linkage map consists of 18,613 scaffolds comprising 515 Mb, representing 56% of the genome and 75% of genic and nonrepetitive regions. There are 18 large (> 10 Mb) LGs, likely representing the expected 18 haploid chromosomes, and > 50% of the genome has been assigned to LGs of at least 17 Mb. Comparisons with other gastropod genomes reveal patterns of synteny and chromosomal rearrangements. Linkage relationships of key immune-relevant genes may help clarify snail–schistosome interactions. By focusing on linkage among genic and nonrepetitive regions, we have generated a useful resource for associating snail phenotypes with causal genes, even in the absence of a complete genome assembly. A similar approach could potentially improve numerous poorly-assembled genomes in other taxa. This map will facilitate future work on this host of a serious human parasite.

Linkage maps are widely used to investigate structure, function, and evolution of genomes. In speciation research, maps facilitate the study of the genetic architecture of reproductive isolation by allowing identification of genomic regions underlying reduced fitness of hybrids. Here we present a linkage map for European newts of the Lissotriton vulgaris species complex, constructed using two families of F2 L. montandoni × L. vulgaris hybrids. The map consists of 1146 protein-coding genes on 12 linkage groups, equal to the haploid chromosome number, with a total length of 1484 cM (1.29 cM per marker). It is notably shorter than two other maps available for salamanders, but the differences in map length are consistent with cytogenetic estimates of the number of chiasmata per chromosomal arm. Thus, large salamander genomes do not necessarily translate into long linkage maps, as previously suggested. Consequently, salamanders are an excellent model to study evolutionary consequences of recombination rate variation in taxa with large genomes and a similar number of chromosomes. A complex pattern of transmission ratio distortion (TRD) was detected: TRD occurred mostly in one family, in one breeding season, and was clustered in two genomic segments. This is consistent with environment-dependent mortality of individuals carrying L. montandoni alleles in these two segments and suggests a role of TRD blocks in reproductive isolation. The reported linkage map will empower studies on the genomic architecture of divergence and interactions between the genomes of hybridizing newts.

Diploidization, which follows whole genome duplication events, does not occur evenly across the genome. In salmonid fishes, certain pairs of homeologous chromosomes preserve tetraploid loci in higher frequencies toward the telomeres due to residual tetrasomic inheritance. Research suggests this occurs only in homeologous pairs where one chromosome arm has undergone a fusion event. We present a linkage map for Arctic charr (Salvelinus alpinus), a salmonid species with relatively fewer chromosome fusions. Genotype by sequencing identified 19,418 SNPs, and a linkage map consisting of 4508 markers was constructed from a subset of high quality SNPs and microsatellite markers that were used to anchor the new map to previous versions. Both male- and female-specific linkage maps contained the expected number of 39 linkage groups. The chromosome type associated with each linkage group was determined, and 10 stable metacentric chromosomes were identified, along with a chromosome polymorphism involving the sex chromosome AC04. Two instances of a weak form of pseudolinkage were detected in the telomeric regions of homeologous chromosome arms in both female and male linkage maps. Chromosome arm homologies within the Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) genomes were determined. Paralogous sequence variants (PSVs) were identified, and their comparative BLASTn hit locations showed that duplicate markers exist in higher numbers on seven pairs of homeologous arms, previously identified as preserving tetrasomy in salmonid species. Homeologous arm pairs where neither arm has been part of a fusion event in Arctic charr had fewer PSVs, suggesting faster diploidization rates in these regions.

By combining 7077 SNPs and 61 microsatellites, we present the first linkage map for some of the early diverged lineages of the common frog, Rana temporaria, and the densest linkage map to date for this species. We found high homology with the published linkage maps of the Eastern and Western lineages but with differences in the order of some markers. Homology was also strong with the genome of the Tibetan frog Nanorana parkeri and we found high synteny with the clawed frog Xenopus tropicalis. We confirmed marked heterochiasmy between sexes and detected nonrecombining regions in several groups of the male linkage map. Contrary to the expectations set by the male heterogamety of the common frog, we did not find male heterozygosity excess in the chromosome previously shown to be linked to sex determination. Finally, we found blocks of loci showing strong transmission ratio distortion. These distorted genomic regions might be related to genetic incompatibilities between the parental populations, and are promising candidates for further investigation into the genetic basis of speciation and adaptation in the common frog.

High density linkage maps are useful tools for fine-scale mapping of quantitative trait loci, and characterization of the recombination landscape of a species’ genome. Genomic resources for Atlantic salmon (Salmo salar) include a well-assembled reference genome, and high density single nucleotide polymorphism (SNP) arrays. Our aim was to create a high density linkage map, and to align it with the reference genome assembly. Over 96,000 SNPs were mapped and ordered on the 29 salmon linkage groups using a pedigreed population comprising 622 fish from 60 nuclear families, all genotyped with the ‘ssalar01’ high density SNP array. The number of SNPs per group showed a high positive correlation with physical chromosome length (r = 0.95). While the order of markers on the genetic and physical maps was generally consistent, areas of discrepancy were identified. Approximately 6.5% of the previously unmapped reference genome sequence was assigned to chromosomes using the linkage map. Male recombination rate was lower than females across the vast majority of the genome, but with a notable peak in subtelomeric regions. Finally, using RNA-Seq data to annotate the reference genome, the mapped SNPs were categorized according to their predicted function, including annotation of ∼2500 putative nonsynonymous variants. The highest density SNP linkage map for any salmonid species has been created, annotated, and integrated with the Atlantic salmon reference genome assembly. This map highlights the marked heterochiasmy of salmon, and provides a useful resource for salmonid genetics and genomics research.

Obligate parthenogenesis (OP) is often thought to evolve by disruption of reductional meiosis and suppression of crossover recombination. In the crustacean Daphnia pulex, OP lineages, which have evolved from cyclical parthenogenetic (CP) ancestors, occasionally produce males that are capable of reductional meiosis. Here, by constructing high-density linkage maps, we find that these males show only slightly and nonsignificantly reduced recombination rates compared to CP males and females. Both meiosis disruption and recombination suppression are therefore sex-limited (or partly so), which speaks against the evolution of OP by disruption of a gene that is essential for meiosis or recombination in both sexes. The findings may be explained by female-limited action of genes that suppress recombination, but previously identified candidate genes are known to be expressed in both sexes. Alternatively, and equally consistent with the data, OP might have evolved through a reuse of the parthenogenesis pathways already present in CP and through their extension to all events of oogenesis. The causal mutations for the CP to OP transition may therefore include mutations in genes involved in oogenesis regulation and may not necessarily be restricted to genes of the "meiosis toolkit." More generally, our study emphasizes that there are many ways to achieve asexuality, and elucidating the possible mechanisms is key to ultimately identify the genes and traits involved., (© The Author(s) 2023. Published by Oxford University Press on behalf of The Society for the Study of Evolution (SSE).)

The silkworm (Bombyx mori) is an important lepidopteran model insect and an industrial domestic animal traditionally used for silk production. Here, we report the genome assembly of an improved Japanese strain Nichi01, in which the cocoon yield is comparable to that of commercial silkworm strains. The integration of PacBio Sequel II long-read and ddRAD-seq-based high-density genetic linkage map achieved the highest quality genome assembly of silkworms to date; 22 of the 28 pseudomolecules contained telomeric repeats at both ends, and only four gaps were present in the assembly. A total of 452 Mbp of the assembly with an N50 of 16.614 Mbp covered 99.3% of the complete orthologs of the lepidopteran core genes. Although the genome sequence of Nichi01 and that of the previously reported low-yielding tropical strain p50T assured their accuracy in most regions, we corrected several regions, misassembled in p50T, in our assembly. A total of 18,397 proteins were predicted using over 95 Gb of mRNA-seq derived from 10 different organs, covering 96.9% of the complete orthologs of the lepidopteran core genes. The final assembly and annotation files are available in KAIKObase (https://kaikobase.dna.affrc.go.jp/index.html) along with a genome browser and BLAST searching service, which would facilitate further studies and the breeding of silkworms and other insects., Competing Interests: Conflict of interest statement The authors declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© The Author(s) 2023. Published by Oxford University Press on behalf of the Genetics Society of America.)

Within the genus Salix, there are approximately 350 species native primarily to the northern hemisphere and adapted to a wide range of habitats. This diversity can be exploited to mine novel alleles conferring variation important for production as a bioenergy crop, but also to identify evolutionarily important genes, such as those involved in sex determination. To leverage this diversity, we created a mapping population by crossing 6 Salix species (Salix viminalis, Salix suchowensis, Salix integra, Salix koriyanagi, Salix udensis, and Salix alberti) to common male and female Salix purpurea parents. Each family was genotyped via genotyping-by-sequencing and assessed for kinship and population structure as well as the construction of 16 backcross linkage maps to be used as a genetic resource for breeding and selection. Analyses of population structure resolved both the parents and F1 progeny to their respective phylogenetic section and indicated that the S. alberti parent was misidentified and was most likely S.suchowensis. Sex determining regions were identified on Salix chromosome 15 in the female-informative maps for seven of the eight families indicating that these species share a common female heterogametic ZW sex system. The eighth family, S. integra × S. purpurea, was entirely female and had a truncated chromosome 15. Beyond sex determination, the Salix F1 hybrid common parent population (Salix F1 HCP) introduced here will be useful in characterizing genetic factors underlying complex traits, aid in marker-assisted selection, and support genome assemblies for this promising bioenergy crop., (© The Author(s) 2022. Published by Oxford University Press on behalf of Genetics Society of America.)

Growth directly influences production rate and therefore is one of the most important and well-studied traits in animal breeding. However, understanding the genetic basis of growth has been hindered by its typically complex polygenic architecture. Here, we performed quantitative trait locus mapping and genome-wide association studies for 10 growth traits that were observed over 2 years in 1,100 F1 captive-bred trevally (Pseudocaranx georgianus). We constructed the first high-density linkage map for trevally, which included 19,861 single nucleotide polymorphism markers, and discovered 8 quantitative trait loci for height, length, and weight on linkage groups 3, 14, and 18. Using genome-wide association studies, we further identified 113 single nucleotide polymorphism-trait associations, uncovering 10 genetic hot spots involved in growth. Two of the markers found in the genome-wide association studies colocated with the quantitative trait loci previously mentioned, demonstrating that combining quantitative trait locus mapping and genome-wide association studies represents a powerful approach for the identification and validation of loci controlling complex traits. This is the first study of its kind for trevally. Our findings provide important insights into the genetic architecture of growth in this species and supply a basis for fine mapping quantitative trait loci, genomic selection, and further detailed functional analysis of the genes underlying growth in trevally., (© The Author(s) 2022. Published by Oxford University Press on behalf of Genetics Society of America.)

The number and placement of meiotic crossover events during meiosis have important implications for the fidelity of chromosome segregation as well as patterns of inheritance. Despite the functional importance of recombination, recombination landscapes vary widely among and within species, and this can have a strong impact on evolutionary processes. A good knowledge of recombination landscapes is important for model systems in evolutionary and ecological genetics, since it can improve interpretation of genomic patterns of differentiation and genome evolution, and provides an important starting point for understanding the causes and consequences of recombination rate variation. Arabidopsis arenosa is a powerful evolutionary genetic model for studying the molecular basis of adaptation and recombination rate evolution. Here, we generate genetic maps for 2 diploid A. arenosa individuals from distinct genetic lineages where we have prior knowledge that meiotic genes show evidence of selection. We complement the genetic maps with cytological approaches to map and quantify recombination rates, and test the idea that these populations might have distinct patterns of recombination. We explore how recombination differs at the level of populations, individuals, sexes and genomic regions. We show that the positioning of crossovers along a chromosome correlates with their number, presumably a consequence of crossover interference, and discuss how this effect can cause differences in recombination landscape among sexes or species. We identify several instances of female segregation distortion. We found that averaged genome-wide recombination rate is lower and sex differences subtler in A. arenosa than in Arabidopsis thaliana., (© The Author(s) 2022. Published by Oxford University Press on behalf of Genetics Society of America.)

Genomic analysis of hybrid zones offers unique insights into emerging reproductive isolation and the dynamics of introgression. Because hybrid genomes consist of blocks inherited from one or the other parental taxon, linkage information is essential. In most cases, the spectrum of local ancestry tracts can be efficiently uncovered from dense linkage maps. Here, we report the development of such a map for the hybridizing toads, Bombina bombina and Bombina variegata (Anura: Bombinatoridae). Faced with the challenge of a large (7-10 Gb), repetitive genome, we set out to identify a large number of Mendelian markers in the nonrepetitive portion of the genome that report B. bombina vs B. variegata ancestry with appropriately quantified statistical support. Bait sequences for targeted enrichment were selected from a draft genome assembly, after filtering highly repetitive sequences. We developed a novel approach to infer the most likely diplotype per sample and locus from the raw read mapping data, which is robust to over-merging and obviates arbitrary filtering thresholds. Validation of the resulting map with 4755 markers underscored the large-scale synteny between Bombina and Xenopus tropicalis. By assessing the sex of late-stage F2 tadpoles from histological sections, we identified the sex-determining region in the Bombina genome to 7 cM on LG5, which is homologous to X. tropicalis chromosome 5, and inferred male heterogamety. Interestingly, chromosome 5 has been repeatedly recruited as a sex chromosome in anurans with XY sex determination., (© The Author(s) 2021. Published by Oxford University Press on behalf of Genetics Society of America.)

The sustainability of many crops is hindered by the lack of genomic resources and a poor understanding of natural genetic diversity. Particularly, application of modern breeding requires high-density linkage maps that are integrated into a highly contiguous reference genome. Here, we present a rapid method for deriving haplotypes and developing linkage maps, and its application to Mentha suaveolens, one of the diploid progenitors of cultivated mints. Using sequence-capture via DNA hybridization to target single nucleotide polymorphisms (SNPs), we successfully genotyped ∼5000 SNPs within the genome of >400 individuals derived from a self cross. After stringent quality control, and identification of nonredundant SNPs, 1919 informative SNPs were retained for linkage map construction. The resulting linkage map defined a total genetic space of 942.17 cM divided among 12 linkage groups, ranging from 56.32 to 122.61 cM in length. The linkage map is in good agreement with pseudomolecules from our preliminary genome assembly, proving this resource effective for the correction and validation of the reference genome. We discuss the advantages of this method for the rapid creation of linkage maps., (© The Author(s) 2021. Published by Oxford University Press on behalf of Genetics Society of America.)

Marasmius oreades is a basidiomycete fungus that grows in so called "fairy rings," which are circular, underground mycelia common in lawns across temperate areas of the world. Fairy rings can be thought of as natural, long-term evolutionary experiments. As each ring has a common origin and expands radially outwards over many years, different sectors will independently accumulate mutations during growth. The genotype can be followed to the next generation, as mushrooms producing the sexual spores are formed seasonally at the edge of the ring. Here, we present new genomic data from 95 single-spore isolates of the species, which we used to construct a genetic linkage map and an updated version of the genome assembly. The 44-Mb assembly was anchored to 11 linkage groups, producing chromosome-length scaffolds. Gene annotation revealed 13,891 genes, 55% of which contained a pfam domain. The repetitive fraction of the genome was 22%, and dominated by retrotransposons and DNA elements of the KDZ and Plavaka groups. The level of assembly contiguity we present is so far rare in mushroom-forming fungi, and we expect studies of genomics, transposons, phylogenetics, and evolution to be facilitated by the data we present here of the iconic fairy-ring mushroom., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.)

The comma butterfly (Polygonia c-album, Nymphalidae, Lepidoptera) is a model insect species, most notably in the study of phenotypic plasticity and plant-insect coevolutionary interactions. In order to facilitate the integration of genomic tools with a diverse body of ecological and evolutionary research, we assembled the genome of a Swedish comma using 10X sequencing, scaffolding with matepair data, genome polishing, and assignment to linkage groups using a high-density linkage map. The resulting genome is 373 Mb in size, with a scaffold N50 of 11.7 Mb and contig N50 of 11,2Mb. The genome contained 90.1% of single-copy Lepidopteran orthologs in a BUSCO analysis of 5,286 genes. A total of 21,004 gene-models were annotated on the genome using RNA-Seq data from larval and adult tissue in combination with proteins from the Arthropoda database, resulting in a high-quality annotation for which functional annotations were generated. We further documented the quality of the chromosomal assembly via synteny assessment with Melitaea cinxia. The resulting annotated, chromosome-level genome will provide an important resource for investigating coevolutionary dynamics and comparative analyses in Lepidoptera., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.)

Squamate reptiles exhibit high variation in their phenotypic traits and geographical distributions and are therefore fascinating taxa for evolutionary and ecological research. However, genomic resources are very limited for this group of species, consequently inhibiting research efforts. To address this gap, we assembled a high-quality genome of the common lizard, Zootoca vivipara (Lacertidae), using a combination of high coverage Illumina (shotgun and mate-pair) and PacBio sequencing data, coupled with RNAseq data and genetic linkage map generation. The 1.46-Gb genome assembly has a scaffold N50 of 11.52 Mb with N50 contig size of 220.4 kb and only 2.96% gaps. A BUSCO analysis indicates that 97.7% of the single-copy Tetrapoda orthologs were recovered in the assembly. In total, 19,829 gene models were annotated to the genome using a combination of ab initio and homology-based methods. To improve the chromosome-level assembly, we generated a high-density linkage map from wild-caught families and developed a novel analytical pipeline to accommodate multiple paternity and unknown father genotypes. We successfully anchored and oriented almost 90% of the genome on 19 linkage groups. This annotated and oriented chromosome-level reference genome represents a valuable resource to facilitate evolutionary studies in squamate reptiles., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.)

Currently available genome assemblies for Atlantic cod ( Gadus morhua ) have been constructed from fish belonging to the Northeast Arctic Cod (NEAC) population; a migratory population feeding in the Barents Sea. These assemblies have been crucial for the development of genetic markers which have been used to study population differentiation and adaptive evolution in Atlantic cod, pinpointing four discrete islands of genomic divergence located on linkage groups 1, 2, 7 and 12. In this paper, we present a high-quality reference genome from a male Atlantic cod representing a southern population inhabiting the Celtic sea. The genome assembly (gadMor&#95;Celtic) was produced from long-read nanopore data and has a combined contig length of 686 Mb with an N50 of 10 Mb. Integrating contigs with genetic linkage mapping information enabled us to construct 23 chromosome sequences which mapped with high confidence to the latest NEAC population assembly (gadMor3) and allowed us to characterize, to an extent not previously reported large chromosomal inversions on linkage groups 1, 2, 7 and 12. In most cases, inversion breakpoints could be located within single nanopore contigs. Our results suggest the presence of inversions in Celtic cod on linkage groups 6, 11 and 21, although these remain to be confirmed. Further, we identified a specific repetitive element that is relatively enriched at predicted centromeric regions. Our gadMor&#95;Celtic assembly provides a resource representing a 'southern' cod population which is complementary to the existing 'northern' population based genome assemblies and represents the first step toward developing pan-genomic resources for Atlantic cod., (Copyright © 2020 Kirubakaran et al.)

Although seed and pod traits are important for peanut breeding, little is known about the inheritance of these traits. A recombinant inbred line (RIL) population of 156 lines from a cross of Tifrunner x NC 3033 was genotyped with the Axiom&#95;Arachis1 SNP array and SSRs to generate a genetic map composed of 1524 markers in 29 linkage groups (LG). The genetic positions of markers were compared with their physical positions on the peanut genome to confirm the validity of the linkage map and explore the distribution of recombination and potential chromosomal rearrangements. This linkage map was then used to identify Quantitative Trait Loci (QTL) for seed and pod traits that were phenotyped over three consecutive years for the purpose of developing trait-associated markers for breeding. Forty-nine QTL were identified in 14 LG for seed size index, kernel percentage, seed weight, pod weight, single-kernel, double-kernel, pod area and pod density. Twenty QTL demonstrated phenotypic variance explained (PVE) greater than 10% and eight more than 20%. Of note, seven of the eight major QTL for pod area, pod weight and seed weight (PVE >20% variance) were attributed to NC 3033 and located in a single linkage group, LG B06&#95;1. In contrast, the most consistent QTL for kernel percentage were located on A07/B07 and derived from Tifrunner., (Copyright © 2020 Chavarro et al.)

Understanding the genomic basis of adaptative intraspecific phenotypic variation is a central goal in conservation genetics and evolutionary biology. Lake trout ( Salvelinus namaycush ) are an excellent species for addressing the genetic basis for adaptive variation because they express a striking degree of ecophenotypic variation across their range; however, necessary genomic resources are lacking. Here we utilize recently-developed analytical methods and sequencing technologies to (1) construct a high-density linkage and centromere map for lake trout, (2) identify loci underlying variation in traits that differentiate lake trout ecophenotypes and populations, (3) determine the location of the lake trout sex determination locus, and (4) identify chromosomal homologies between lake trout and other salmonids of varying divergence. The resulting linkage map contains 15,740 single nucleotide polymorphisms (SNPs) mapped to 42 linkage groups, likely representing the 42 lake trout chromosomes. Female and male linkage group lengths ranged from 43.07 to 134.64 centimorgans, and 1.97 to 92.87 centimorgans, respectively. We improved the map by determining coordinates for 41 of 42 centromeres, resulting in a map with 8 metacentric chromosomes and 34 acrocentric or telocentric chromosomes. We use the map to localize the sex determination locus and multiple quantitative trait loci (QTL) associated with intraspecific phenotypic divergence including traits related to growth and body condition, patterns of skin pigmentation, and two composite geomorphometric variables quantifying body shape. Two QTL for the presence of vermiculations and spots mapped with high certainty to an arm of linkage group Sna3, growth related traits mapped to two QTL on linkage groups Sna1 and Sna12, and putative body shape QTL were detected on six separate linkage groups. The sex determination locus was mapped to Sna4 with high confidence. Synteny analysis revealed that lake trout and congener Arctic char ( Salvelinus alpinus ) are likely differentiated by three or four chromosomal fissions, possibly one chromosomal fusion, and 6 or more large inversions. Combining centromere mapping information with putative inversion coordinates revealed that the majority of detected inversions differentiating lake trout from other salmonids are pericentric and located on acrocentric and telocentric linkage groups. Our results suggest that speciation and adaptive divergence within the genus Salvelinus may have been associated with multiple pericentric inversions occurring primarily on acrocentric and telocentric chromosomes. The linkage map presented here will be a critical resource for advancing conservation oriented genomic research on lake trout and exploring chromosomal evolution within and between salmonid species., (Copyright © 2020 Smith et al.)

The rate of meiotic recombination is one of the central factors determining genome-wide levels of linkage disequilibrium which has important consequences for the efficiency of natural selection and for the dissection of quantitative traits. Here we present a new, high-resolution linkage map for Populus tremula that we use to anchor approximately two thirds of the P. tremula draft genome assembly on to the expected 19 chromosomes, providing us with the first chromosome-scale assembly for P. tremula (Table 2). We then use this resource to estimate variation in recombination rates across the P. tremula genome and compare these results to recombination rates based on linkage disequilibrium in a large number of unrelated individuals. We also assess how variation in recombination rates is associated with a number of genomic features, such as gene density, repeat density and methylation levels. We find that recombination rates obtained from the two methods largely agree, although the LD-based method identifies a number of genomic regions with very high recombination rates that the map-based method fails to detect. Linkage map and LD-based estimates of recombination rates are positively correlated and show similar correlations with other genomic features, showing that both methods can accurately infer recombination rate variation across the genome. Recombination rates are positively correlated with gene density and negatively correlated with repeat density and methylation levels, suggesting that recombination is largely directed toward gene regions in P. tremula ., (Copyright © 2020 Apuli et al.)

The genus Rhododendron (Ericaceae), which includes horticulturally important plants such as azaleas, is a highly diverse and widely distributed genus of >1,000 species. Here, we report the chromosome-scale de novo assembly and genome annotation of Rhododendron williamsianum as a basis for continued study of this large genus. We created multiple short fragment genomic libraries, which were assembled using ALLPATHS-LG. This was followed by contiguity preserving transposase sequencing (CPT-seq) and fragScaff scaffolding of a large fragment library, which improved the assembly by decreasing the number of scaffolds and increasing scaffold length. Chromosome-scale scaffolding was performed by proximity-guided assembly (LACHESIS) using chromatin conformation capture (Hi-C) data. Chromosome-scale scaffolding was further refined and linkage groups defined by restriction-site associated DNA (RAD) sequencing of the parents and progeny of a genetic cross. The resulting linkage map confirmed the LACHESIS clustering and ordering of scaffolds onto chromosomes and rectified large-scale inversions. Assessments of the R. williamsianum genome assembly and gene annotation estimate them to be 89% and 79% complete, respectively. Predicted coding sequences from genome annotation were used in syntenic analyses and for generating age distributions of synonymous substitutions/site between paralgous gene pairs, which identified whole-genome duplications (WGDs) in R. williamsianum. We then analyzed other publicly available Ericaceae genomes for shared WGDs. Based on our spatial and temporal analyses of paralogous gene pairs, we find evidence for two shared, ancient WGDs in Rhododendron and Vaccinium (cranberry/blueberry) members that predate the Ericaceae family and, in one case, the Ericales order., (© The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.)

Medaka ( Oryzias sp.) is an important fish species in ecotoxicology and considered as a model species due to its biological features including small body size and short generation time. Since Japanese medaka Oryzias latipes is a freshwater species with access to an excellent genome resource, the marine medaka Oryzias melastigma is also applicable for the marine ecotoxicology. In genome era, a high-density genetic linkage map is a very useful resource in genomic research, providing a means for comparative genomic analysis and verification of de novo genome assembly. In this study, we developed a high-density genetic linkage map for O. melastigma using restriction-site associated DNA sequencing (RAD-seq). The genetic map consisted of 24 linkage groups with 2,481 single nucleotide polymorphism (SNP) markers. The total map length was 1,784 cM with an average marker space of 0.72 cM. The genetic map was integrated with the reference-assisted chromosome assembly (RACA) of O. melastigma , which anchored 90.7% of the assembled sequence onto the linkage map. The values of complete Benchmarking Universal Single-Copy Orthologs were similar to RACA assembly but N50 (23.74 Mb; total genome length 779.4 Mb; gap 5.29%) increased to 29.99 Mb (total genome length 778.7 Mb; gap 5.2%). Using MapQTL analysis with SNP markers, we identified a major quantitative trait locus for sex traits on the Om10. The integration of the genetic map with the reference genome of marine medaka will serve as a good resource for studies in molecular toxicology, genomics, CRISPR/Cas9, and epigenetics., (Copyright © 2019 Lee et al.)

Platycladus orientalis is an ecologically important native conifer in Northern China and exotic species in many parts of the world; however, knowledge about the species' genetics and genome are very limited. The availability of well-developed battery of genetic markers, with large genome coverage, is a prerequisite for the species genetic dissection of adaptive attributes and efficient selective breeding. Here, we present a genome-wide genotyping method with double-digestion restriction site associated DNA sequencing (ddRAD-seq) that is effective in generating large number of Mendelian markers for genome mapping and other genetic applications. Using 139 megagametophytes collected from a single mother tree, we assembled 397,226 loci, of which 108,683 (27.4%) were polymorphic. After stringent filtering for 1:1 segregation ratio and missing rate of <20%, the remaining 23,926 loci (22% of the polymorphic loci) were ordered into 11 linkage groups (LGs) and distributed across 7,559 unique positions, with a total map length of 1,443 cM and an average spacing of 0.2 cM between adjacent unique positions. The 11 LGs correspond to the species' 11 haploid genome chromosome number. This genetic map is among few high-density maps available for conifers to date, and represents the first genetic map for P. orientalis The information generated serves as a solid foundation not only for marker-assisted breeding efforts, but also for comparative conifer genomic studies., (Copyright © 2019 Jin et al.)

Cultivated chrysanthemum (Chrysanthemum morifolium Ramat.) is one of the most economically important ornamental crops grown worldwide. It has a complex hexaploid genome (2n = 6x = 54) and large genome size. The diploid Chrysanthemum seticuspe is often used as a model of cultivated chrysanthemum, since the two species are closely related. To expand our knowledge of the cultivated chrysanthemum, we here performed de novo whole-genome assembly in C. seticuspe using the Illumina sequencing platform. XMRS10, a C. seticuspe accession developed by five generations of self-crossing from a self-compatible strain, AEV2, was used for genome sequencing. The 2.72 Gb of assembled sequences (CSE&#95;r1.0), consisting of 354,212 scaffolds, covered 89.0% of the 3.06 Gb C. seticuspe genome estimated by k-mer analysis. The N50 length of scaffolds was 44,741 bp. For protein-encoding genes, 71,057 annotated genes were deduced (CSE&#95;r1.1&#95;cds). Next, based on the assembled genome sequences, we performed linkage map construction, gene discovery and comparative analyses for C. seticuspe and cultivated chrysanthemum. The generated C. seticuspe linkage map revealed skewed regions in segregation on the AEV2 genome. In gene discovery analysis, candidate flowering-related genes were newly found in CSE&#95;r1.1&#95;cds. Moreover, single nucleotide polymorphism identification and annotation on the C. × morifolium genome showed that the C. seticuspe genome was applicable to genetic analysis in cultivated chrysanthemums. The genome sequences assembled herein are expected to contribute to future chrysanthemum studies. In addition, our approach demonstrated the usefulness of short-read genome assembly and the importance of choosing an appropriate next genome sequencing technology based on the purpose of the post-genome analysis., (© The Author(s) 2019. Published by Oxford University Press on behalf of Kazusa DNA Research Institute.)

Characterizing the genetic variation underlying phenotypic traits is a central objective in biological research. This research has been hampered in the past by the limited genomic resources available for most non-model species. However, recent advances in sequencing technologies and related genotyping methods are rapidly changing this. Here we report the use of genome-wide SNP data from the ecologically and commercially important marine fish species Chrysophrys auratus (snapper) to 1) construct the first linkage map for this species, 2) scan for growth QTL, and 3) search for putative candidate genes in the surrounding QTL regions. The newly constructed linkage map contained ∼11K SNP markers and is one of the densest maps to date in the fish family Sparidae. Comparisons with genome scaffolds of the recently assembled snapper genome indicated that marker placement was mostly consistent between the scaffolds and linkage map (R = 0.7), but that at fine scales (< 5 cM) some precision limitations occurred. Of the 24 linkage groups, which likely reflect the 24 chromosomes of this species, three were found to contain QTL with genome-wide significance for growth-related traits. A scan of 13 candidate growth genes located the growth hormone, myogenin, and parvalbumin genes within 5.3, 9.6, and 25.0 cM of these QTL, respectively. The linkage map and QTL found in this study will advance the investigation of genome structure and aquaculture breeding efforts in this and related species., (Copyright © 2019 Ashton et al.)

Genome structure characterization can contribute to a better understanding of processes such as adaptation, speciation, and karyotype evolution, and can provide useful information for refining genome assemblies. We studied the genome of an important North American boreal forest pest, the spruce budworm, Choristoneura fumiferana , through a combination of molecular cytogenetic analyses and construction of a high-density linkage map based on single nucleotide polymorphism (SNP) markers obtained through a genotyping-by-sequencing (GBS) approach. Cytogenetic analyses using fluorescence in situ hybridization methods confirmed the haploid chromosome number of n = 30 in both sexes of C. fumiferana and showed, for the first time, that this species has a WZ/ZZ sex chromosome system. Synteny analysis based on a comparison of the Bombyx mori genome and the C. fumiferana linkage map revealed the presence of a neo-Z chromosome in the latter species, as previously reported for other tortricid moths. In this neo-Z chromosome, we detected an ABC transporter C2 ( ABCC2 ) gene that has been associated with insecticide resistance. Sex-linkage of the ABCC2 gene provides a genomic context favorable to selection and rapid spread of resistance against Bacillus thuringiensis serotype kurstaki (Btk), the main insecticide used in Canada to control spruce budworm populations. Ultimately, the linkage map we developed, which comprises 3586 SNP markers distributed over 30 linkage groups for a total length of 1720.41 cM, will be a valuable tool for refining our draft assembly of the spruce budworm genome., (Copyright © 2018 Picq et al.)

Ostreid herpesvirus (OsHV) can cause mass mortality events in Pacific oyster aquaculture. While various factors impact on the severity of outbreaks, it is clear that genetic resistance of the host is an important determinant of mortality levels. This raises the possibility of selective breeding strategies to improve the genetic resistance of farmed oyster stocks, thereby contributing to disease control. Traditional selective breeding can be augmented by use of genetic markers, either via marker-assisted or genomic selection. The aim of the current study was to investigate the genetic architecture of resistance to OsHV in Pacific oyster, to identify genomic regions containing putative resistance genes, and to inform the use of genomics to enhance efforts to breed for resistance. To achieve this, a population of ∼1,000 juvenile oysters were experimentally challenged with a virulent form of OsHV, with samples taken from mortalities and survivors for genotyping and qPCR measurement of viral load. The samples were genotyped using a recently-developed SNP array, and the genotype data were used to reconstruct the pedigree. Using these pedigree and genotype data, the first high density linkage map was constructed for Pacific oyster, containing 20,353 SNPs mapped to the ten pairs of chromosomes. Genetic parameters for resistance to OsHV were estimated, indicating a significant but low heritability for the binary trait of survival and also for viral load measures (h2 0.12 - 0.25). A genome-wide association study highlighted a region of linkage group 6 containing a significant QTL affecting host resistance. These results are an important step toward identification of genes underlying resistance to OsHV in oyster, and a step toward applying genomic data to enhance selective breeding for disease resistance in oyster aquaculture., (Copyright © 2018 Gutierrez et al.)

High-density linkage maps are an important tool to gain insight into the genetic architecture of traits of evolutionary and economic interest, and provide a resource to characterize variation in recombination landscapes. Here, we used information from the cattle genome and the 50 K Cervine Illumina BeadChip to inform and refine a high-density linkage map in a wild population of red deer ( Cervus elaphus ). We constructed a predicted linkage map of 38,038 SNPs and a skeleton map of 10,835 SNPs across 34 linkage groups. We identified several chromosomal rearrangements in the deer lineage relative to sheep and cattle, including six chromosome fissions, one fusion, and two large inversions. Otherwise, our findings showed strong concordance with map orders in the cattle genome. The sex-averaged linkage map length was 2739.7 cM and the genome-wide autosomal recombination rate was 1.04 cM/Mb. The female autosomal map length was 1.21 longer than that of males (2767.4 cM vs. 2280.8 cM, respectively). Sex differences in map length were driven by high female recombination rates in peri-centromeric regions, a pattern that is unusual relative to other mammal species. This effect was more pronounced in fission chromosomes that would have had to produce new centromeres. We propose two hypotheses to explain this effect: (1) that this mechanism may have evolved to counteract centromeric drive associated with meiotic asymmetry in oocyte production; and/or (2) that sequence and structural characteristics suppressing recombination in close proximity to the centromere may not have evolved at neo-centromeres. Our study provides insight into how recombination landscapes vary and evolve in mammals, and will provide a valuable resource for studies of evolution, genetic improvement, and population management in red deer and related species., (Copyright © 2017 Johnston et al.)

Linkage maps are widely used to investigate structure, function, and evolution of genomes. In speciation research, maps facilitate the study of the genetic architecture of reproductive isolation by allowing identification of genomic regions underlying reduced fitness of hybrids. Here we present a linkage map for European newts of the Lissotriton vulgaris species complex, constructed using two families of F2 L. montandoni × L. vulgaris hybrids. The map consists of 1146 protein-coding genes on 12 linkage groups, equal to the haploid chromosome number, with a total length of 1484 cM (1.29 cM per marker). It is notably shorter than two other maps available for salamanders, but the differences in map length are consistent with cytogenetic estimates of the number of chiasmata per chromosomal arm. Thus, large salamander genomes do not necessarily translate into long linkage maps, as previously suggested. Consequently, salamanders are an excellent model to study evolutionary consequences of recombination rate variation in taxa with large genomes and a similar number of chromosomes. A complex pattern of transmission ratio distortion (TRD) was detected: TRD occurred mostly in one family, in one breeding season, and was clustered in two genomic segments. This is consistent with environment-dependent mortality of individuals carrying L. montandoni alleles in these two segments and suggests a role of TRD blocks in reproductive isolation. The reported linkage map will empower studies on the genomic architecture of divergence and interactions between the genomes of hybridizing newts., (Copyright © 2017 Niedzicka et al.)

The aquatic planorbid snail Biomphalaria glabrata is one of the most intensively-studied mollusks due to its role in the transmission of schistosomiasis. Its 916 Mb genome has recently been sequenced and annotated, but it remains poorly assembled. Here, we used targeted capture markers to map over 10,000 B. glabrata scaffolds in a linkage cross of 94 F1 offspring, generating 24 linkage groups (LGs). We added additional scaffolds to these LGs based on linkage disequilibrium (LD) analysis of targeted capture and whole-genome sequences of 96 unrelated snails. Our final linkage map consists of 18,613 scaffolds comprising 515 Mb, representing 56% of the genome and 75% of genic and nonrepetitive regions. There are 18 large (> 10 Mb) LGs, likely representing the expected 18 haploid chromosomes, and > 50% of the genome has been assigned to LGs of at least 17 Mb. Comparisons with other gastropod genomes reveal patterns of synteny and chromosomal rearrangements. Linkage relationships of key immune-relevant genes may help clarify snail-schistosome interactions. By focusing on linkage among genic and nonrepetitive regions, we have generated a useful resource for associating snail phenotypes with causal genes, even in the absence of a complete genome assembly. A similar approach could potentially improve numerous poorly-assembled genomes in other taxa. This map will facilitate future work on this host of a serious human parasite., (Copyright © 2017 Tennessen et al.)

Diploidization, which follows whole genome duplication events, does not occur evenly across the genome. In salmonid fishes, certain pairs of homeologous chromosomes preserve tetraploid loci in higher frequencies toward the telomeres due to residual tetrasomic inheritance. Research suggests this occurs only in homeologous pairs where one chromosome arm has undergone a fusion event. We present a linkage map for Arctic charr ( Salvelinus alpinus ), a salmonid species with relatively fewer chromosome fusions. Genotype by sequencing identified 19,418 SNPs, and a linkage map consisting of 4508 markers was constructed from a subset of high quality SNPs and microsatellite markers that were used to anchor the new map to previous versions. Both male- and female-specific linkage maps contained the expected number of 39 linkage groups. The chromosome type associated with each linkage group was determined, and 10 stable metacentric chromosomes were identified, along with a chromosome polymorphism involving the sex chromosome AC04. Two instances of a weak form of pseudolinkage were detected in the telomeric regions of homeologous chromosome arms in both female and male linkage maps. Chromosome arm homologies within the Atlantic salmon ( Salmo salar ) and rainbow trout ( Oncorhynchus mykiss ) genomes were determined. Paralogous sequence variants (PSVs) were identified, and their comparative BLASTn hit locations showed that duplicate markers exist in higher numbers on seven pairs of homeologous arms, previously identified as preserving tetrasomy in salmonid species. Homeologous arm pairs where neither arm has been part of a fusion event in Arctic charr had fewer PSVs, suggesting faster diploidization rates in these regions., (Copyright © 2017 Nugent et al.)