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A morphospecies is defined as a taxonomic species based wholly on morphology, but often morphospecies consist of clusters of cryptic species that can be identified genetically or molecularly. The nature of the evolutionary novelty that accompanies speciation in a morphospecies is an intriguing question. Morphospecies are particularly common among ciliates, a group of unicellular eukaryotes that separates 2 kinds of nuclei-the silenced germline nucleus (micronucleus [MIC]) and the actively expressed somatic nucleus (macronucleus [MAC])-within a common cytoplasm. Because of their very similar morphologies, members of the Tetrahymena genus are considered a morphospecies. We explored the hidden genomic evolution within this genus by performing a comprehensive comparative analysis of the somatic genomes of 10 species and the germline genomes of 2 species of Tetrahymena. These species show high genetic divergence; phylogenomic analysis suggests that the genus originated about 300 million years ago (Mya). Seven universal protein domains are preferentially included among the species-specific (i.e., the youngest) Tetrahymena genes. In particular, leucine-rich repeat (LRR) genes make the largest contribution to the high level of genome divergence of the 10 species. LRR genes can be sorted into 3 different age groups. Parallel evolutionary trajectories have independently occurred among LRR genes in the different Tetrahymena species. Thousands of young LRR genes contain tandem arrays of exactly 90-bp exons. The introns separating these exons show a unique, extreme phase 2 bias, suggesting a clonal origin and successive expansions of 90-bp-exon LRR genes. Identifying LRR gene age groups allowed us to document a Tetrahymena intron length cycle. The youngest 90-bp exon LRR genes in T. thermophila are concentrated in pericentromeric and subtelomeric regions of the 5 micronuclear chromosomes, suggesting that these regions act as genome innovation centers. Copies of a Tetrahymena Long interspersed element (LINE)-like retrotransposon are very frequently found physically adjacent to 90-bp exon/intron repeat units of the youngest LRR genes. We propose that Tetrahymena species have used a massive exon-shuffling mechanism, involving unequal crossing over possibly in concert with retrotransposition, to create the unique 90-bp exon array LRR genes.
Pubmed ID: 31158217 RIS Download
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View all literature mentionsSoftware program for phylogenetic analyses of large datasets under maximum likelihood.
View all literature mentionsWeb application to generate sequence logos, graphical representations of patterns within multiple sequence alignment. Designed to make generation of sequence logos easy. Sequence logo generator.
View all literature mentionsSoftware tool as whole genome shotgun assembler that can generate high quality genome assemblies using short reads (~100bp) such as those produced by the new generation of sequencers.
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View all literature mentionsSoftware tool that screens DNA sequences for interspersed repeats and low complexity DNA sequences. The output of the program is a detailed annotation of the repeats that are present in the query sequence as well as a modified version of the query sequence in which all the annotated repeats have been masked (default: replaced by Ns). Currently over 56% of human genomic sequence is identified and masked by the program. Sequence comparisons in RepeatMasker are performed by one of several popular search engines including nhmmer, cross_match, ABBlast/WUBlast, RMBlast and Decypher. RepeatMasker makes use of curated libraries of repeats and currently supports Dfam ( profile HMM library ) and RepBase ( consensus sequence library ).
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View all literature mentionsPackage of programs for phylogenetic analyses of DNA or protein sequences using maximum likelihood. PAML estimates parameters and tests hypotheses to study the evolutionary process from a phylogenetic tree.
View all literature mentionsSequence analysis software that performs repeat family identification and creates models for sequence data. RepeatModeler utilizes RepeatScout and RECON to identify repeat element boundaries and family relationships.
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