Platypus Genome Provides Unique Insights into Early Mammalian Evolution and Monotreme Biology

Abstract

Whole‐genome sequence has been available from species of two mammalian subclasses (marsupials and eutherian mammals) but not monotreme mammals. Monotremes (platypus and echidna) are the most distant living mammalian relatives to humans, which diverged more than 160 million years ago. In addition to the key phylogenetic position they also feature fascinating biology (e.g. egg‐laying, venom, electroreception and multiple sex chromosomes). The recently completed draft genome of the duck‐billed platypus fills this gap in comparative genomics, and provides unique insights into the evolution of mammalian genes, regulatory mechanisms and nonprotein‐coding sequences. The platypus genome project also revealed first insights into the gene sets underlying the unique biology of monotremes. Key concepts: Monotremes are the most basal mammalian group of egg‐laying mammals (including platypuses and echidnas) that provide unique insights into the evolution of mammals. Mammals are a group of animals, which share fur, mammary glands and a placenta. This group includes eutheria (e.g. humans and mice), metatheria (e.g. kangaroos) and prototheria (egg‐laying platypus and echidna). Genomics describes the analysis of sequences of whole genomes. In Comparative Genomics information on genomes of various species is compared to provide insights into the evolutionary change of different aspects of genomes (e.g. chromosomes, genes, regulatory regions and repeats). Rapid progress in large‐scale DNA sequencing technology allows Genome Projects to determine the sequence of entire genomes of a rapidly growing number of organisms. Genome composition describes basic characteristics of whole genomes including size, estimated gene number, repeat content and base pair composition. Genome analysis provides a prediction of most of the genes in a genome, which reveals presence or absence of genes and gives insights into function and evolution of typical characteristics of the species. All genetic information generated by publicly funded genome projects or published by individual researchers are deposited in Genome databases (also called genome browsers like UCSC or ENSEMBL) which allow searches and comparisons of billions of sequences of hundreds of species.