HSA4 and GGA4: Remarkable conservation despite 300-Myr divergence

The chicken (GGA) and human (HSA) genomes diverged around 300-350 Myr ago. Due to this large phylogenetic distance, significant synteny conservation h as not been anticipated between the genomes of the two species, However, Zo o-FISH with HSA4 chromosome-specific paint on chicken metaphase chromosomes shows that the human chromosome corresponds largely to the GGA4cen-->q26 r egion. Comparative gene mapping data in the two species, though limited, pr ovide strong support for these observations. The findings, together with th e very recently published data on HSA9-GGAZ and HSA12-GCA1, show that some large chromosomal segments share conserved synteny in the two species. Thes e syntenies are considerably disrupted in the mouse. This makes us believe that despite very early divergence, parts of the human and chicken genomes are more conserved than those of human and mouse, which radiated only 100-1 20 Myr ago. Moreover, the HSA4-GGA4q correspondence points to a "candidate" chromosome from the karyotype of a mammal-bird ancestor. The findings are thus a small but important step toward understanding the evolution of the t wo genomes. (C) 2000 Academic Press.