Human (Homo sapiens) and chimpanzee (Pan troglodytes) share similar ancestral centromeric alpha satellite DNA sequences but other fractions of heterochromatin differ considerably

Abstract

The euchromatic regions of chimpanzee (Pan troglodytes) genome share approximately 98% sequence similarity with the human (Homo sapiens), while the heterochromatic regions display considerable divergence. Positive heterochromatic regions revealed by the CBG-technique are confined to pericentromeric areas in humans, while in chimpanzees, these regions are pericentromeric, telomeric, and intercalary. When human chromosomes are digested with restriction endonuclease AluI and stained by Giemsa (AluI/Giemsa), positive heterochromatin is detected only in the pericentromeric regions, while in chimpanzee, telomeric, pericentromeric, and in some chromosomes both telomeric and centromeric, regions are positive. The DA/DAPI technique further revealed extensive cytochemical heterogeneity of heterochromatin in both species. Nevertheless, the fluorescence in situ hybridization technique (FISH) using a centromeric alpha satellite cocktail probe revealed that both primates share similar pericentromeric alpha satellite DNA sequences. Furthermore, cross-hybridization experiments using chromosomes of gorilla (Gorilla gorilla) and orangutan (Pongo pygmaeus) suggest that the alphoid repeats of human and great apes are highly conserved, implying that these repeat families were present in their common ancestor. Nevertheless, the orangutan's chromosome 9 did not cross-hybridize with human probe.