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.
Paralytic polio. In rare cases, poliovirus infection leads to paralytic polio, the most serious form of the disease. Paralytic polio has several types, based on the part of your body that's affected â your spinal cord (spinal polio), your brainstem (bulbar polio) or both (bulbospinal polio). Initial signs and symptoms of paralytic polio, such as fever and headache, often mimic those of nonparalytic polio.