Genetic counterselective procedure to isolate interspecific cell hybrids containing single human chromosomes: construction of cell hybrids and recombinant DNA libraries specific for human chromosomes 3 and 4.

Counterselection against genes on human chromosome 5 was applied to interspecific human-Chinese hamster cell hybrids which retained this and one additional human chromosome in order to generate cell hybrids retaining single, nonselected human chromosomes. Using this procedure, stable cell hybrids which retain human chromosome 3 exclusively or human chromosome 4 exclusively were isolated. Complete recombinant genomic DNA libraries were prepared from each hybrid using the lambda cloning vector EMBL-4. These libraries represent sources of human DNA fragments derived specifically from chromosomes 3 and 4, respectively. Low-copy or unique human DNA fragments isolated from both libraries were analyzed to confirm their chromosomal origin and to determine the complexity of their hybridization patterns to total human DNA. These single human chromosome libraries represent a means to efficiently saturate chromosomes 3 and 4 with informative, polymorphic genetic markers. DNA fragments from the chromosome 4 library will be particularly useful in identifying additional genetic markers close to the Huntington's disease gene. The same genetic counterselective procedure can be utilized to derive several additional cell hybrids with single human chromosomes.