SMAD4 is a tumor suppressor gene located on chromosome 18 that is known to be homozygously deleted in human lung cancer. If you were to perform comparative genomic hybridization with tissue from a lung cancer patient with a homozygous negative SMAD4 tumor, what ratio of green to red fluorescence would you expect?
A)A ratio of 1 on all of chromosome 18.
B)A ratio of 2 on the part of chromosome 18 containing the SMAD4 gene, with a value of 1 on the remainder of the chromosome.
C)A ratio of 0 on all of chromosome 18.
D)A ratio of 0 on the part of chromosome 18 containing the SMAD4 gene, with a value of 1 on the remainder of the chromosome.
E) A ratio of 1 on the part of chromosome 18 containing the SMAD4 gene, with a value of 0 on the remainder of the chromosome.
F)
A ratio of 0.5 on the part of chromosome 18 containing the SMAD gene, with a value of 1 on the remainder of the chromosome.

Question

Quizplus · Accepted Answer

A homozygous deletion of the SMAD4 gene would result in a loss of one copy of chromosome 18, which would be detected as a ratio value of 0 (lack of red fluorescence) on the part of the chromosome that contains the SMAD4 gene. The rest of the chromosome would still have two copies, resulting in a ratio value of 1 (equal parts of green and red fluorescence). Therefore, choice D is the correct answer.

SMAD4 Is a Tumor Suppressor Gene Located on Chromosome 18