Phylogenetic origin of human chromosomes 7, 16, and 19 and their homologs in placental mammals

The origin of human chromosomes (HSA) 7, 16, and 19 was studied by comparin g data obtained from chromosome banding, chromosome painting, and gene mapp ing in species belonging to II orders of placental mammals (Eutherians). Th is allowed us to propose the reconstruction of their presumed ancestral for ms. The HSA7 homologs were composed of two parts, the largest Forming an ac rocentric. The smallest formed one al-m of a small submetacentric; the othe r arm was composed of sequences homologous to the short arm of HSA16 (HSA16 p). The sequences homologous to the long arm of HSA16 (HSA16q) were associa ted with sequences homologous to the long arm of HSA19 (HSA19q) and formed another submetacentric. from their origin, these chromosomes underwent the following rearrangements to give rise to current human chromosomes: centrom eric fission of the two submetacentrics in ancestors of all primates (simil ar to 80 million years ago); fusion of the HSA19p and HSA19q sequences, ori ginating the current HSA19, in ancestors of all simians (similar to 55 mill ion years ago); fusions of the HSA16p and HSA16q sequences, originating the current HSA16 and the two components of HSA7 before the separation of Cerc opithecoids and Hominoids (similar to 35 million years ago); and finally, p ericentric and paracentric inversions of the homologs to HSA7 after the div ergence of orangutan and gorilla, respectively. Thus, competed with HSA16 a nd HSA19, HSA7 is a Fairly recent chromosome shared by man and chimpanzee o nly.