3/6/2023 0 Comments Genodive problems![]() ![]() Due to the time and expense of assessing segregation within progeny arrays for every locus and every individual or species compared, it has not been quantified how frequently deviations from strictly disomic or strictly polysomic inheritance occur. Moreover, inheritance patterns can vary across the genome within individuals, leading to disomic inheritance at some loci and polysomic at others. In cases for which the homoeologous chromosomes can pair in meiosis and produce viable gametes, allopolyploids also may show a mixture of disomic and polysomic inheritance patterns. With sufficient divergence between homoeologues, meiotic pairing only takes place between chromosomes from the same parental origin, leading to disomic inheritance. derived from different ancestral species) homoeologues (see Box 1). Allopolyploids originate after hybridization of different species and subsequent genome doubling so that each chromosome is represented by two (or more) sets of divergent chromosomes, in which chromosomes within a set are termed homologues, and chromosomes from different sets (i.e. However, even in autopolyploids divergence, neo-functionalization, or loss of duplicate copies over time (Lynch & Conery 2000) inevitably leads to disomic inheritance for at least some loci (Ohno 1970). These homologous copies theoretically can at least initially pair in all possible combinations, leading to polysomic inheritance. Autopolyploids originate after genome doubling within a single species, so that each chromosome is represented by more than two homologous copies. Polyploids are typically classified as either autopolyploids or allopolyploids (Stebbins 1947). This is largely due to the more complex nature of their genome evolution. This has led to the generally accepted view that polyploidization plays an important role in evolution, in both plants and animals.ĭespite the important role of polyploidization in evolution, our basic understanding of polyploids is still poor compared with diploids. A whole-genome duplication event is thought to have facilitated the survival of flowering plant lineages during the mass extinction events during the Cretaceous-Tertiary transition (Fawcett et al. In animals, whole-genome duplication events have coincided with the origin of vertebrates, gnathostomes and teleosts (Holland et al. In plants and yeast, early genome-sequencing projects revealed that numerous diploid species show signs of ancient genome duplications (Arabidopsis, Blanc et al. Even organisms that are now genetically diploid often have a paleopolyploid history. Although polyploidy is much rarer in the animal kingdom than in plants, there are numerous examples of polyploid invertebrates, fish and amphibians (Gregory & Mable 2005 Mable et al. Polyploidy is a prominent feature of plant genomes (Tate et al. In addition, there is a need for more simulation-based studies that test what kinds of biases could result from both existing and novel approaches. This leads us to conclude that for advancing the field of polyploid population genetics, most priority should be given to development of new molecular approaches that allow efficient dosage determination, and to further development of analytical approaches to circumvent dosage uncertainty and to accommodate ‘flexible’ modes of inheritance. These problems are in most cases directly associated with dosage uncertainty and the problem of inferring allele frequencies and assumptions regarding inheritance. In addition, we review the approaches that have been used for population genetic analysis in polyploids and their specific problems. We review commonly used molecular tools (amplified fragment length polymorphism, microsatellites, Sanger sequencing, next-generation sequencing and derived technologies) and their challenges associated with their use in polyploid populations: that is, allele dosage determination, null alleles, difficulty of distinguishing orthologues from paralogues and copy number variation. This review aims to provide an overview of the state-of-the-art in polyploid population genetics and to identify the main areas where further development of molecular techniques and statistical theory is required. Furthermore, many of the standard tools for population genetics that have been developed for diploids are often not feasible for polyploids. multiple alleles and loci, mixed inheritance patterns, association between ploidy and mating system variation). These gaps arise from the complex nature of polyploid data (e.g. Despite the importance of polyploidy and the increasing availability of new genomic data, there remain important gaps in our knowledge of polyploid population genetics. ![]()
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