Fluorescent in situ hybridization (FISH) was employed in mapping the 
alpha-satellite DNA that was revealed in the cosmid libraries specific for human 
chromosomes 13, 21, and 22. In total, 131 clones were revealed. They contained 
various elements of centromeric alphoid DNA sequences of acrocentric 
chromosomes, including those located close to SINEs, LINEs, and classical 
satellite sequences. The heterochromatin of acrocentric chromosomes was shown to 
contain two different groups of alphoid sequences: (1) those immediately 
adjacent to the centromeric regions (alpha 13-1, alpha 21-1, and alpha 22-1 
loci) and (2) those located in the short arm of acrocentric chromosomes (alpha 
13-2, alpha 21-2, and alpha 22-2 loci). Alphoid DNA sequences from the alpha 
13-2, alpha 21-2, and alpha 22-2 loci are apparently not involved in the 
formation of centromeres and are absent from mitotically stable marker 
chromosomes with a deleted short arm. Robertsonian translocations t(13q; 21q) 
and t(14q; 22q), and chromosome 21p-. The heterochromatic regions of chromosomes 
13, 21, and 22 were also shown to contain relatively chromosome-specific 
repetitive sequences of various alphoid DNA families, whose numerous copies 
occur in other chromosomes. Pools of centromeric alphoid cosmids can be of use 
in further studies of the structural and functional properties of 
heterochromatic DNA and the identification of centromeric sequences. Moreover, 
these clones can be employed in high-resolution mapping and in sequencing the 
heterochromatic regions of the human genome. The detailed FISH analysis of 
numerous alphoid cosmid clones allowed the identification of several new, highly 
specific DNA probes of molecular cytogenetic studies--in particular, the 
interphase and metaphase analyses of chromosomes 2, 9, 11, 14, 15, 16, 18, 20, 
21-13, 22-14, and X.