Final answer:
The gene of interest is likely located in the upper 75% of chromosome 13, as evidenced by the somatic-cell hybridization experiment where only the cell line with complete deletion of chromosome 13 failed to produce the gene product.
Step-by-step explanation:
Based on the details provided in the somatic-cell hybridization experiment, the gene of interest is likely located on chromosome 13. Since the gene product is produced in the two cell lines that either have an intact chromosome 13 or have lost the lower 25% of chromosome 13, this strongly indicates that the gene is located in the upper 75% of chromosome 13. In contrast, the gene product is not produced in the cell line missing chromosome 13 entirely. Therefore, this data suggests that the absence of the gene on chromosome 13 leads to a lack of gene product expression.
From the context of gene linkage and the principles of genetic mapping, when genes are closer together on a chromosome, they tend to be inherited together during meiosis. Inversely, if genes are further apart, there is an increased probability of crossover events separating them, which is used by geneticists to create linkage maps. Given the experiment's results and understanding of chromosome painting and karyotyping, the question highlights how somatic-cell hybridization can indicate gene location.