Anaphase Promoting Complex (APC) is a protein degradation machinery necessary for proper mitosis of animal cells. If APC is defective in human cells, which of the following is expected to occur?
a. Recombination of chromosome arms will occur.
b. Chromosomes will not condense.
c. Chromosomes will be fragmented.
d. Chromosomes will not segregate.

Answer

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Hint: Anaphase Promoting Complex (APC) is a multisubunit ubiquitin-protein ligase that targets for degradation cell-cycle.

Complete Answer:
Anaphase-promoting complex (APC) is a multi-subunit ubiquitin ligase. It plays a major role in the progression of the eukaryotic cell cycle.

Option a: Recombination of chromosome arms occurs during the prolonged prophase of Meiosis I. Prophase I is the longest and most important segment of meiosis.

Option b: Condensation of chromosomes occurs in the prophase of mitosis. The chromatin in a cell compacts to form condensed chromosomes. Condensation of the chromosome is required so that cells divide properly.

Option c: Fragmentation of chromosome is a phenomenon that takes place during mitosis. It occurs when chromosomes are damaged either by drug treatment or when a damaged cell passes through the G2 checkpoint.

Option d: Anaphase promoting complex (APC) helps in the transition of the chromosome from metaphase to anaphase. The role of APC is that it attaches to the chromosomes aligned at the equator during metaphase and allows the segregation of the chromatids.

Thus, the correct option is d) Chromosomes will not segregate.

Note: It is to be noted that Anaphase-Promoting promotes the onset of anaphase by marking Cyclin B1 and securin for proteasomal destruction.