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Genome diversity and karyotype evolution of mammals
The 2000s witnessed an explosion of genome sequencing and mapping in evolutionarily diverse species. While full genome sequencing of mammals is rapidly progressing, the ability to assemble and align orthologous whole chromosomal regions from more than a few species is not yet possible. The intense focus on the building of comparative maps for domestic (dogs and cats), laboratory (mice and rats) and agricultural (cattle) animals has traditionally been used to understand the underlying basis of disease-related and healthy phenotypes. However, these maps also provide an unprecedented opportunity to use multispecies analysis as a tool to infer karyotype evolution. Comparative chromosome painting and related techniques are very powerful approaches in comparative genome studies. Homologies can be identified with high accuracy using molecularly defined DNA probes for fluorescence ''in situ'' hybridization (FISH) on chromosomes of different species. Chromosome painting data are now available for members of nearly all mammalian orders. It was found that in most orders, there are species with rates of chromosome evolution that can be considered as 'default' rates. It needs to be noted that the number of rearrangements that have become fixed in evolutionary history seems relatively low, due to 180 million years of the mammalian radiation. Thus a record of the history of karyotype changes that have occurred during evolution have been attained through comparative chromosome maps.
==Mammalian phylogenomics==
Modern mammals (class ''Mammalia'') are divided into Monotremes, Marsupials, and Placentals. The subclass Prototheria (''Monotremes'') comprises the five species of egg-laying mammals: platypus and four echidna species. The infraclasses Metatheria (''Marsupials'') and Eutheria (''Placentals'') together form the subclass Theria. In the 2000s understanding of the relationships among eutherian mammals has experienced a virtual revolution. Molecular phylogenomics, new fossil finds and innovative morphological interpretations now group the more than 4600 extant species of eutherians into four major super-ordinal clades: Euarchontoglires (including Primates, Dermoptera, Scandentia, Rodentia, and Lagomorpha), Laurasiatheria (Cetartiodactyla, Perissodactyla, Carnivora, Chiroptera, Pholidota, and Eulipotyphla), Xenarthra, and Afrotheria (Proboscidea, Sirenia, Hyracoidea, Afrosoricida, Tubulidentata, and Macroscelidea). This tree is very useful in unifying the parts of a puzzle in comparative mammalian cytogenetics.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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