The phylogeny of human chromosome specific alpha satellites.

The chromosomal distribution of sequences homologous to 18 coned alpha satellite fragments was established by in situ hybridization. It appeared that all the cloned sequences were members of small repeated families located on single chromosome pairs. Among the sequences studied specific molecular markers for chromosomes 3, 4, 10, 11, 17, 18 and X were found. Comparison of the hybridization spectra obtained under non-stringent conditions and of restriction site periodicities in different chromosome-specific families allowed the identification of three "suprachromosomal" families, each located on a characteristic set of chromosomes. The three families together cover all the autosomes and the X chromosome. These data plus those reported previously allow part of the phylogenetic tree of chromosome-specific alpha satellite repeats to be drawn. Each suprachromosomal family has presumably originated from a distinct ancestral sequence and consists of certain types of monomers. Ancestral sequences have evolved into a number of chromosome-specific families by cycles of interchromosomal transfers and subsequent amplification events. The high homogeneity of chromosome-specific families may be a result of intrachromosomal homogenization of amplification units in chromosome-specific alpha satellite domains.