Researchers experimentally delete both
copies of the RB transcriptional corepressor 1 (RB1) gene in cultured human
cells. They observe that the cells begin progressing through the G1/S
checkpoint without proper control, leading to uncontrolled proliferation.

Which conclusion best explains this
observation?

Question

Researchers experimentally delete both
copies of the RB transcriptional corepressor 1 (RB1) gene in cultured human
cells. They observe that the cells begin progressing through the G1/S
checkpoint without proper control, leading to uncontrolled proliferation.

Which conclusion best explains this
observation?

Accepted Answer

Loss
of both RB1 alleles removes an important cell-cycle brake, promoting cancer
development

Answer

RB1 functions
primarily as a transcription factor that directly drives cell proliferation,
promoting cancer development

Answer

RB1 normally
activates DNA replication, so its loss blocks cell division

Answer

Activation of a
single RB1 allele is sufficient to cause tumorigenesis

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