Question

Describe the characteristic features observed for metazoan genome evolution. (Min 2 and a half pages.)

Answer 1

Solution

Overall aspects and features

1. In addition to environmental and ecological triggers, biological functions encoded in the genome were crucial in this transition in evolution of characteristic features in metazoa.
2. including genes involved in differential gene regulation (e.g., several transcription factors, signalling pathways), cell adhesion (e.g., cadherins), cell type specification, cell cycle, and immunity.
3. Recent studies show that many genes typically associated with metazoan functions actually pre-date animals themselves, supporting functional co-option of ‘unicellular genes’ during the genesis of metazoans.
4. There are some aspects by which evolution of metazoa is possible more.which are given below

Mitochondrial features

• (1) the plasticity of Metazoa mtDNA is higher than previously thought and mainly due to variation in number and location of tRNA genes;
• (2) an exceptional trend towards stabilization of genomic features occurred in deuterostomes and was exacerbated in vertebrates, where gene content, genome architecture and gene strand asymmetry are almost invariant.
• Only tunicates exhibit a very high degree of genome variability comparable to that found outside deuterostomes. In order to analyse the genomic evolutionary process at short evolutionary distances, we have also compared mtDNAs of species belonging to the same genus: the variability observed in congeneric species significantly recapitulates the evolutionary dynamics observed at higher taxonomic ranks, especially for taxa showing high levels of genome plasticity and/or fast nucleotide substitution rates.

Morphological aspect

• The animal kingdom exhibits a great diversity of organismal form (i.e., disparity).
• Whether the extremes of disparity were achieved early in animal evolutionary history or clades continually explore the limits of possible morphospace is subject to continuing debate.
• Here we show, through analysis of the disparity of the animal kingdom, that, even though many clades exhibit maximal initial disparity, arthropods, chordates, annelids, echinoderms, and mollusks have continued to explore and expand the limits of morphospace throughout the Phanerozoic, expanding dramatically the envelope of disparity occupied in the Cambrian. The “clumpiness” of morphospace occupation by living clades is a consequence of the extinction of phylogenetic intermediates, indicating that the original distribution of morphologies was more homogeneous.
• The morphological distances between phyla mirror differences in complexity, body size, and species-level diversity across the animal kingdom. Causal hypotheses of morphologic expansion include time since origination, increases in genome size, protein repertoire, gene family expansion, and gene regulation.
• We find a strong correlation between increasing morphological disparity, genome size, and microRNA repertoire, but no correlation to protein domain diversity.
• Our results are compatible with the view that the evolution of gene regulation has been influential in shaping metazoan disparity whereas the invasion of terrestrial ecospace appears to represent an additional gestalt, underpinning the post-Cambrian expansion of metazoan disparity.