A series of cystic fibrosis homozygous fibroblast X mouse cell hybrids were constructed in order to determine the chromosome which carries the gene controlling the cystic fibrosis mucociliary inhibitor (CFMI) phenotype. Several hybrids and their subclones retained the CFMI phenotype for long periods in cell culture. Correlation of the CFMI phenotype with the presence of specific human chromosomes indicated that possible linkage existed between CFMI and human chromosomes 2, 4, 6, 10, and 18. The strongest chance of linkage existed for chromosome 4.

The expression of the gene coding for the cystic fibrosis ciliary inhibitor has been examined in somatic cell hybrid clonal lines. Hybrids were produced by the fusion of cultured skin fibroblasts from cystic fibrosis patients with mouse RAG and LM (TK-) cell lines. The ciliary inhibitor was detected by the oyster ciliary assay in several primary hybrid clones but not detected in others, indicating the segregation of an associated nuclear gene.