Abstract
The increase in huge number of genomic sequences in recent years has contributed to various genetic events such as horizontal gene transfer (HGT), gene duplication and hybridization of species. Among them HGT has played an important role in the genome evolution and was believed to occur only in Bacterial and Archaeal genomes. As a result, genomes were found to be chimeric and the evolution of life was represented in different forms such as forests, networks and species evolution was described more like a rhizome, rather than a tree. However, in the last few years, HGT has also been evidenced in other group such as metazoa (for example in root-knot nematodes, bdelloid rotifers and mammals). In addition to HGT, other genetic events such as transfer by retrotransposons and hybridization between more closely related lineages are also well established. Therefore, in the light of such genetic events, whether the evolution of metazoa exists in the form of a tree, network or rhizome is highly questionable and needs to be determined. In the current review, we will focus on the role of HGT, retrotransposons and hybridization in the metazoan evolution.
Highlights
The rapid increase in molecular and genomic data in recent years have contributed to genetic events such as horizontal gene transfer (HGT), that is often considered as a major constraint in the reconstruction of phylogenetic trees
CONCLUDING REMARKS The relative amount of HGT events detected in metazoa merely represent just tip of an iceberg
There are still many outstanding questions that need to be addressed like: What is the rate of gene transfer within the group? How important is gene transfer in other animal genomes, especially vertebrates? There are many lineages that need to be considered for HGT, such as Rotifers, Aves, Reptiles and Mammals
Summary
The increase in the prevalence of HGT events in Bacteria, Archaea, and Eukaryotes have resulted in the chimeric nature of genomes, where different parts of the genome can have different evolutionary histories and its difficult to identify a single common ancestor for the gene repertoire of any organism All these results have conferred to undermine the TOL concept, thereby giving rise to a new paradigm. Recent studies on whole genomic sequences from various metazoan phyla suggest a chimeric origin for its major groups due to the presence of HGT and hybridization (Syvanen and Ducore, 2010) The results from these studies pose new questions about the evolution of metazoa, as whether it exists in the form of network or rhizome of life? We will discuss the role of HGT, transfer by retrotransposons, hybridization and the challenges that it proposes for the current metazoan evolutionary paradigm
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