Retinoblastoma is an extremely rare cancer of the retina in the eye. The disease mainly affects children up to the age of 5 years because it can only occur while the nerve precursor cells are still dividing. In its nonhereditary form, a tumor usually occurs in only one eye; in its hereditary form, multiple tumors develop in both eyes. To explore the basis for these differences, a cDNA clone of the Rb gene was used to probe the structure of the gene in cells from normal individuals and from individuals with nonhereditary or hereditary retinoblastoma. As shown in the figure Part A, normal individuals have four restriction fragments (A, B, C, and D) that hybridize to the Rb cDNA probe, indicating that each restriction fragment encodes at least one Rb exon. Samples from fibroblasts and tumor cells of affected persons show some differences in the patterns of hybridization, with some bands missing entirely and some bands present at half intensity. The order of the restriction fragments in the Rb gene is shown in Part B. Why do the band patterns differ in the fibroblasts and tumor cells from the same person? A. Tumor cells differ from fibroblasts because they have lost portions of the Rb gene. B. Tumor cells differ because they have suffered nucleotide changes in the Rb gene. C. Tumor cells differ from fibroblasts because they have inherited different Rb genes. D. Tumor cells differ because they derive from nerve cell precursors, not fibroblasts.
Retinoblastoma is an extremely rare cancer of the retina in the eye. The disease mainly affects children up to the age of 5 years because it can only occur while the nerve precursor cells are still dividing. In its nonhereditary form, a tumor usually occurs in only one eye; in its hereditary form, multiple tumors develop in both eyes.
To explore the basis for these differences, a cDNA clone of the Rb gene was used to probe the structure of the gene in cells from normal individuals and from individuals with nonhereditary or hereditary retinoblastoma. As shown in the figure Part A, normal individuals have four restriction fragments (A, B, C, and D) that hybridize to the Rb cDNA probe, indicating that each restriction fragment encodes at least one Rb exon. Samples from fibroblasts and tumor cells of affected persons show some differences in the patterns of hybridization, with some bands missing entirely and some bands present at half intensity. The order of the restriction fragments in the Rb gene is shown in Part B.
Why do the band patterns differ in the fibroblasts and tumor cells from the same person?
A. Tumor cells differ from fibroblasts because they have lost portions of the Rb gene.
B. Tumor cells differ because they have suffered
C. Tumor cells differ from fibroblasts because they have inherited different Rb genes.
D. Tumor cells differ because they derive from nerve cell precursors, not fibroblasts.
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