Question

1. during interphase of the cell cycle, a growing cell undergoes dna replication. what is the primary function of dna replication?

a to create haploid sex cells to be used in reproduction
b to edit the dna code and correct mistakes
c to add genetic variation through mutations and the process of crossing - over
d to provide an exact copy of dna to daughter cells once the cell divides

1. the diagram below summarizes the three checkpoints that ensure that cells successfully complete the cell cycle to create healthy daughter cells.

spindle checkpoint:

• all chromosomes are attached to the spindle during metaphase.

g₂ checkpoint:

• dna is not damaged.
• dna was replicated completely and correctly.

g₁ checkpoint:

• cell is sufficient size.
• cell has sufficient energy and nutrients.
• cell is receiving signals to divide.
• dna is not damaged.

aneuploidy is defined as an abnormal number of chromosomes in a cell. aneuploidy is observed in many types of cancer cells. which of the following events occurring during the cell cycle would be most directly implicated in creating aneuploid cells?
a a cell does not receive external signals to divide and therefore cannot complete the g₁ phase.
b a cell of insufficient size completes the g₁ phase of the cell cycle.
c dna is damaged and not repaired completely at the g₂ checkpoint.
d an error occurs at the spindle checkpoint that results in nondisjunction of one or more chromosomes.

Explanation:

Question 18

• Option A: Creating haploid sex cells is meiosis, not interphase DNA replication.
• Option B: Editing DNA and correcting mistakes is DNA repair, not replication’s main role.
• Option C: Mutations and crossing - over (in meiosis) aren't the primary function of interphase DNA replication.
• Option D: During cell division (mitosis or meiosis), daughter cells need an exact DNA copy, which is provided by DNA replication in interphase.

• Option A: Not entering \(G_1\) phase won't cause aneuploidy (abnormal chromosome number) as no division - related chromosome issues occur.
• Option B: Cell size in \(G_1\) phase doesn't directly relate to chromosome number abnormalities.
• Option C: DNA damage at \(G_2\) checkpoint affects DNA integrity, not chromosome number.
• Option D: Spindle checkpoint ensures chromosomes attach to spindles. If it fails (nondisjunction), chromosomes won't separate properly, leading to abnormal chromosome numbers (aneuploidy).

Answer:

D. to provide an exact copy of DNA to daughter cells once the cell divides

Question 19