Genome resulting from the mating of closely related species
Glossary
Ancestry block/introgression tracts - a region in the genome of a hybrid where all alleles are inherited from the same parent species.
Allopolyploid species - a polyploid hybrid species where the two chromosome sets are derived from different parent species.
Backcrossing - crossing of a hybrid with one of its parent species.
Extrinsic incompatibilities - Environment-dependent reproductive barrier. For example, when trait combinations lead to reduced fitness in the hybrid offspring in specific environments.
Genome stabilization - the process by which different ancestry blocks or introgression tracts become fixed within a hybrid species when hybridization between the hybrid taxon and its parent taxa has ceased.
Hybrid - offspring resulting from interbreeding between two genetically distinct taxa, e.g. breeds or species.
Hybrid genome - The genome of a hybrid individual, characterized by the presence of ancestry tracts from different species. This review focuses mainly on hybrid genomes that result in separate lineages.
Hybrid zone - geographical area in which two taxa (e.g. species or breeds) interbreed resulting in hybrid offspring.
Homoploid hybridization - the formation of a hybrid with no change in chromosome number.
Incomplete lineage sorting - when gene trees produced by single polymorphic sites or genetic regions deviate from the species level tree by chance. Such deviations between gene and species trees can arise from random fixation of alleles that were segregating in the ancestor. At each gene tree, taxa that fixed the same allele will show closer phylogenetic similarity than taxa that fixed different alleles.
Introgressive hybridization - hybridization resulting in the transfer of a gene or genetic tract from one species into the gene pool of another species by repeated backcrossing.
Linkage disequilibrium - the non-random association of alleles at different loci in a given population. The association can arise either through physical linkage for genes residing on the same chromosome, or through coinheritance of unlinked loci.
Phenology - the study of periodical natural phenomena such as flowering time and bird migration and how these are influenced by season and climatic conditions.
Polyploid hybridization - the formation of a hybrid involving whole genome duplication.
Postzygotic incompatibilities - reproductive barrier arising after zygote formation, including inviability and sterility.
Post-mating barriers - Reproductive barriers that act after mating. These can include barriers that act after mating but before the zygote is formed (Post-mating, pre-zygotic barriers).
Pre-mating barriers - Factors that make individuals more likely to mate with members of their own taxon than of another taxon or prevent mating between the taxa. Examples include sexual traits and preferences that differ between the two taxa, mechanical mismatch during copulation, or mating at different times or in different habitats.
Prezygotic incompatibilities - reproductive barrier acting before fertilization. For example, pollinator isolation, mechanical barriers preventing mating, and sperm/ovule incompatibilities that prevent fertilization.
Reproductive isolation - the presence of barriers to successful crossbreeding. Barriers can be classified in a number of ways depending on their timing and mechanism. For example, barriers can be classified depending whether they act before zygote formation (prezygotic; e.g. pollinator isolation) or after zygote formation (postzygotic; e.g. hybrid inviability). They can also be classified by whether they act in the form of intrinsic barriers reducing viability or fertility in hybrid offspring or extrinsic barriers where hybrid offspring are ecologically less fit than the parents and selected against.
Recombination rate - Recombination is a process during meiosis or mitosis by which pieces of homologous chromosomes are broken and recombined to new combinations. The frequency or rate of such recombination varies across the genome.
Recombinational hybrid speciation - the process by which a hybrid population develops reproductive isolation from the parent species through sorting of incompatibilities leading to combinations that are incompatible with both parent species but compatible within the hybrid taxon.
Transgressive phenotypes - extreme phenotypes in hybrids, exceeding trait values of both parent lineages.
Eukaryote hybrid genomes result from interspecific hybridization, where closely related species mate and produce offspring with admixed genomes. The advent of large-scale genomic sequencing has shown that hybridization is common, and that it may represent an important source of novel variation. Although most interspecific hybrids are sterile or less fit than their parents, some may survive and reproduce, enabling the transfer of adaptive variants across the species boundary, and even result in the formation of novel evolutionary lineages. There are two main variants of hybrid species genomes: allopolyploid, which have one full chromosome set from each parent species, and homoploid, which are a mosaic of the parent species genomes with no increase in chromosome number.
The establishment of hybrid species requires the development of reproductive isolation against parental species. Allopolyploid species often have strong intrinsic reproductive barriers due to differences in chromosome number, and homoploid hybrids can become reproductively isolated from the parent species through assortment of genetic incompatibilities. However, both types of hybrids can become further reproductively isolated, gaining extrinsic isolation barriers, by exploiting novel ecological niches, relative to their parents. Hybrids represent the merging of divergent genomes and thus face problems arising from incompatible combinations of genes. Thus hybrid genomes are highly dynamic and may undergo rapid evolutionary change, including genome stabilization in which selection against incompatible combinations results in fixation of compatible ancestry block combinations within the hybrid species. The potential for rapid adaptation or speciation makes hybrid genomes a particularly exciting subject in evolutionary biology. The article summarizes how introgressed alleles or hybrid species can establish and how the resulting hybrid genomes evolve.
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Eukaryotehybridgenomes result from interspecific hybridization, where closely related species mate and produce offspring with admixed genomes. The advent...
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polymers (presumed to be RNA) that were the precursors to life. Eukaryotehybridgenome Four-gamete test Homologous recombination Independent assortment...
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the completion of the first complete genome sequence of a eukaryote, S. cerevisiae (12.1 Mb), and since then genomes have continued being sequenced at an...
and other important chemical compounds used by the cells of autotrophic eukaryotes. Some contain biological pigments such as used in photosynthesis or which...
viruses over plasmids to bacteria and finally eukaryotes), the assembly programs used in these genome projects needed increasingly sophisticated strategies...
multicellular eukaryote, A. thaliana has a relatively small genome of around 135 megabase pairs. It was the first plant to have its genome sequenced, and...
the structure and sequence of the splice junctions meant, and why eukaryotegenomes were large. Around the same time that Doolittle and Darnell suggested...
the result of genome duplications which occurred at least several million years ago (MYA). Such an event could either double the genome of a single species...
jeffersonianum genomes, while an LTxJTi individual would be a tetraploid with genomes from four species. Because they have hybridgenomes, unisexual salamanders...
genomes are among the smallest genomes of eukaryotes. The sizes of fungal genomes range from less than 10 Mbp to hundreds of Mbp. The average genome size...
with certain supplements. They do retain their own nuclear genome. A cybrid is then a hybrid cell which mixes the nuclear genes from one cell with the...
chromosomes in eukaryotes, and circular chromosomes in prokaryotes. The set of chromosomes in a cell makes up its genome; the human genome has approximately...
analyzing complete genome sequences. Evolutionary trees based only on SSU rRNA alone do not capture the events of early eukaryote evolution accurately...
crossing-over (recombination) in lily and mouse they concluded that diverse eukaryotes share a common pattern. This finding suggested that chromosomal crossing...
significant after metazoan radiation. Evolution of eukaryotes is mediated by sexual recombination of parental genomes and since introns are longer than exons most...
choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals. Choanoflagellates...
completely associated with the SAR clade. The SAR are often seen as eukaryote-eukaryotehybrids, contributing to the confusion in the genetic analyses. A sister...
plants, although there appears to be a core subset of genes present in all eukaryotes (except for the few that have no mitochondria at all). In Fungi, however...
replication. In eukaryotes, ribonuclease H1 is involved in DNA replication of the mitochondrial genome. Both H1 and H2 are involved in genome maintenance...
that hybrid offspring are sterile, but fertile hybrids may result in speciation. hybrid breakdown hybrid incompatibility hybrid inviability hybrid speciation...
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