Polyploidization increases meiotic recombination frequency in Arabidopsis: a close look at statistical modeling and data analysis

This paper is a response to Pecinka A, Fang W, Rehmsmeier M, Levy AA, Mittelsten Scheid, O: Polyploidization increases meiotic recombination frequency in Arabidopsis. BMC Biology 2011, 9:24

Response to Wang and Luo

This article is a response to Wang and Luo

GenomeScope 2.0 and Smudgeplot for Reference-Free Profiling of Polyploid Genomes

An important assessment prior to genome assembly and related analyses is genome profiling, where the k-mer frequencies within raw sequencing reads are analyzed to estimate major genome characteristics such as size, heterozygosity, and repetitiveness. Here we introduce GenomeScope 2.0 (https://github.com/tbenavi1/genomescope2.0), which applies combinatorial theory to establish a detailed mathematical model of how k-mer frequencies are distributed in heterozygous and polyploid genomes. We describe and evaluate a practical implementation of the polyploid-aware mixture model that quickly and accurately infers genome properties across thousands of simulated and several real datasets spanning a broad range of complexity. We also present a method called Smudgeplot (https://github.com/KamilSJaron/smudgeplot) to visualize and estimate the ploidy and genome structure of a genome by analyzing heterozygous k-mer pairs. We successfully apply the approach to systems of known variable ploidy levels in the Meloidogyne genus and the extreme case of octoploid Fragaria × ananassa

Polyploidy breaks speciation barriers in Australian burrowing frogs Neobatrachus

Polyploidy has played an important role in evolution across the tree of life but it is still unclear how polyploid lineages may persist after their initial formation. While both common and well-studied in plants, polyploidy is rare in animals and generally less understood. The Australian burrowing frog genus Neobatrachus is comprised of six diploid and three polyploid species and offers a powerful animal polyploid model system. We generated exome-capture sequence data from 87 individuals representing all nine species of Neobatrachus to investigate species-level relationships, the origin and inheritance mode of polyploid species, and the population genomic effects of polyploidy on genus-wide demography. We describe rapid speciation of diploid Neobatrachus species and show that the three independently originated polyploid species have tetrasomic or mixed inheritance. We document higher genetic diversity in tetraploids, resulting from widespread gene flow between the tetraploids, asymmetric inter-ploidy gene flow directed from sympatric diploids to tetraploids, and isolation of diploid species from each other. We also constructed models of ecologically suitable areas for each species to investigate the impact of climate on differing ploidy levels. These models suggest substantial change in suitable areas compared to past climate, which correspond to population genomic estimates of demographic histories. We propose that Neobatrachus diploids may be suffering the early genomic impacts of climate-induced habitat loss, while tetraploids appear to be avoiding this fate, possibly due to widespread gene flow. Finally, we demonstrate that Neobatrachus is an attractive model to study the effects of ploidy on the evolution of adaptation in animals

Association Mapping Considering Allele Dosage: An Example of Forage Traits in an Interspecific Segmental Allotetraploid Urochloa spp.

The breeding process in tropical segmental allopolyploid forage Urochloa is challenging due to the complex genetic control of the traits. Knowledge about genes associated with forage traits, expressed in the different cutting seasons, are extremely useful to support breeding programs and development of new cultivars. Thus, the aims of our study were (i) to identify genomic regions related to forage traits through genomewide association studies (GWAS), and (ii) to verify the influence of allele dosage on these results. A panel of 272 genotypes of Urochloa spp. [U. brizantha (Hoscht. ex A. Rich.) R. Webster ´ U. ruziziensis (Hoscht. ex A. Rich.) R. Webster] was evaluated in both the wet and dry seasons. The GWAS analyses were performed with 26,535 single nucleotide polymorphisms (SNPs) obtained by genotyping-by-sequencing (GBS) using diploid and tetraploid allele dosage configurations. Furthermore, we evaluated scenarios including additive, dominance, and epistatic effects. Seven candidate genomic regions associated with the main forage traits of Urochloa spp. were identified. The importance of the diploid and tetraploid molecular configuration in GWAS analyses for segmental allopolyploid species was demonstrated to identify the genomic behavior of important regions. Results demonstrated that it is possible to identify the same regions using both ploidy configurations; however, in some cases, the allele substitution effect can be biased mainly for regions with dominance and epistatic effects. Finally, this study contributes to the understanding of genetic control of tropical forage traits and genomics to accelerate the selection and reduce the cost to release new cultivars

PERGOLA: fast and deterministic linkage mapping of polyploids

Background: A large share of agriculturally and horticulturally important plant species are polyploid. Linkage maps are used to locate associations between genes and traits by breeders and geneticists. Linkage map creation for polyploid species is not supported by standard tools. We want to overcome this limitation and validate our results with simulation studies. Results: We developed PERGOLA, a deterministic and heuristic method that addresses this problem. We show that it creates correct linkage groups, marker orders and distances for simulated and real datasets. We compare it to existing tools and demonstrate that it overcomes limitations in ploidy and outperforms them in computational time and mapping accuracy. We represent linkage maps as dendrograms and show that this has advantages in the comparison of different maps. Conclusions: PERGOLA can be used successfully to calculate linkage maps for diploid and polyploid species and outperforms existing tools