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.
Salk's Impact. There were 28,985 cases of polio in 1955, and there were only 14,647 cases in 1956. The Salk vaccine, also called the inactivated polio vaccine (IPV), is credited with the enormous decrease in cases.The vaccine contained three strains of the polio virus, and it provided at least partial immunity.here were 28,985 cases of polio in 1955, and there were only 14,647 cases in 1956. The Salk vaccine, also called the inactivated polio vaccine (IPV), is credited with the enormous decrease in cases.