Figure 2. Evolutionary layers of the X and Y chromosomes. (a) Comparative mapping of genes from the human X in marsupial mammals detected an ancient region conserved on the X in all mammals and denoted XCR, as well as a recently added region denoted XAR that is autosomal in marsupials.
Poliovirus, the causative agent of poliomyelitis (commonly known as polio), is a human enterovirus and member of the family of Picornaviridae. Poliovirus is composed of an RNA genome and a protein capsid. The genome is a single-stranded positive-sense RNA genome that is about 7500 nucleotides long.
Karl Landsteiner and Erwin Popper discovered poliovirus in 1908 by proving that it was not a bacterium that caused the paralysis, but a much smaller entityâa virus.arl Landsteiner and Erwin Popper discovered poliovirus in 1908 by proving that it was not a bacterium that caused the paralysis, but a much smaller entityâa virus.