Somatic cancer cells often are unstable and divide inappropriately (divide when they should not be dividing). In addition such cells often contain losses of some chromosomes and extra copies of other chromosomes. Defects in which of the following may be partially responsible for the aberrant behavior of cancer cells? (Select all that apply.)
A)spindle-assembly checkpoint
B)G1/S checkpoint
C)homologous chromosome pairing
D)crossing over

G1/S checkpoint

Explanation:

G1/S checkpoint is one of the points in the cell cycle, between growth phase 1 and DNA synthesis phase, where a cell that has been damaged is sensed by DNA repair enzymes and further degraded by apoptosis. In cancer cells, there is mutation in these DNA repair enzymes and thus nothing to correct the cells from dividing even when damaged and thus there is no arrest of division and cells continue dividing

A ( spindle assembly checkpoint)

B ( G1/S Checkpoint)

Explanation:

Transitions between phases of the cell cycle are controlled by checkpoints.

This process is regulated by cyclins, cyclin-dependent kinases and tumor suppressors.

A defect at any of these internal checkpoints would result in mutation that would lead to the formation of abnormal cells.

b a mature ovary of a plant.