Microdissection of a human marker chromosome reveals its origin and a new family of centromeric repetitive DNA.

A series of procedures including chromosome microdissection, sequence-independent PCR, Southern-blot-hybrid-selection-cloning and sequencing of microdissected DNA-library members were used to analyze DNA from a familial marker chromosome centromere and to determine the origin of the marker chromosome in the case of a live-born, tetraploid human infant. A new family of repetitive DNA, termed sn5 satellite, was sequenced and characterized by DNA hybridization. The sn5 satellite family appears to be primate-specific and shows a chromosome-specific distribution which parallels that of alpha satellite suprachromosomal family 2. This suprachromosomal classification is based on sequence similarity of centromeric alpha satellite DNA within particular groups of chromosomes. It has been postulated that the similarity of alphoid sequences within each of the three suprachromosomal families results from homologous exchanges between nonhomologous chromosomes within each family. The parallel distribution of sn5 satellite sequences at the centromeres of chromosomes of alphoid suprachromosomal family 2 suggests that homologous exchanges between non-homologous chromosomes may be the basis of simultaneous chromosome-specific sequence conservation for multiple centromeric satellite DNA families.