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.
1894, first outbreak of polio in epidemic form in the U.S. occurs in Vermont, with 132 cases. 1908, Karl Landsteiner and Erwin Popper identify a virus as the cause of polio by transmitting the disease to a monkey. 1916, large epidemic of polio within the United States. 1921, Franklin Delano Roosevelt (FDR) contracts polio at age 39. His example has a major impact on public perceptions of individuals with disabilities.