Q1. Which event occurs during the G₁ phase of the cell cycle? Select all that are true.

Background

Topic: Cell Cycle Phases

This question tests your understanding of the G₁ phase, which is the first gap phase after cell division and before DNA replication. It is important to distinguish what cellular activities occur in G₁ compared to other phases like S, G₂, and M.

Key Terms:

• G₁ phase: The period of cell growth and preparation for DNA replication.

• Gene expression: The process by which information from a gene is used to synthesize proteins.

• DNA replication: The process of copying DNA, which occurs in the S phase.

• Chromosome condensation: Occurs during mitosis/meiosis, not G₁.

• Separation of sister chromatids: Occurs during mitosis/meiosis, not G₁.

Step-by-Step Guidance

1. Review the main events of the G₁ phase: cell growth, gene expression, and preparation for DNA replication.

2. Recall that DNA replication occurs in the S phase, not G₁.

3. Chromosome condensation and separation of sister chromatids occur during mitosis/meiosis, not G₁.

4. Identify which options are specific to G₁ and which belong to other phases.

Try solving on your own before revealing the answer!

Q2. If a cell bypassed the G₁/S checkpoint despite extensive DNA damage, what would most likely result?

Background

Topic: Cell Cycle Checkpoints

This question tests your understanding of the importance of cell cycle checkpoints, especially the G₁/S checkpoint, which prevents cells with damaged DNA from replicating.

Key Terms:

• G₁/S checkpoint: Ensures DNA integrity before replication.

• DNA damage: Can lead to mutations if not repaired.

• Cell division: The process of creating daughter cells.

Step-by-Step Guidance

1. Recall the function of the G₁/S checkpoint: to prevent cells with damaged DNA from entering S phase.

2. Consider what happens if this checkpoint is ignored: damaged DNA is replicated.

3. Think about the consequences for daughter cells if DNA damage is not repaired.

4. Evaluate the options for the most likely outcome.

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Q3. A cell with 2n = 8 undergoes meiosis but experiences nondisjunction of one homologous pair in meiosis I. How many chromosomes will each gamete contain after meiosis II?

Background

Topic: Meiosis and Chromosome Number

This question tests your understanding of nondisjunction, which is the failure of homologous chromosomes to separate properly during meiosis I, resulting in abnormal chromosome numbers in gametes.

Key Terms:

• 2n: Diploid chromosome number.

• Nondisjunction: Failure of chromosome separation.

• Meiosis I and II: Two rounds of division in meiosis.

Step-by-Step Guidance

1. Recall that normal meiosis produces gametes with n chromosomes.

2. Understand that nondisjunction in meiosis I results in two gametes with an extra chromosome and two with one less.

3. Calculate the possible chromosome numbers in the resulting gametes.

4. Set up the calculation for the chromosome distribution after meiosis II.

Try solving on your own before revealing the answer!

Q4. Which event occurs in meiosis II but not in meiosis I?

Background

Topic: Meiosis I vs. Meiosis II

This question tests your ability to distinguish between the events of meiosis I and meiosis II.

Key Terms:

• Meiosis I: Homologous chromosomes separate.

• Meiosis II: Sister chromatids separate.

• Crossing over: Occurs in meiosis I.

• Synapsis: Occurs in meiosis I.

• Reduction of chromosome number: Occurs in meiosis I.

Step-by-Step Guidance

1. List the events unique to meiosis I: crossing over, synapsis, reduction of chromosome number.

2. List the events unique to meiosis II: separation of sister chromatids.

3. Compare the options to determine which event is exclusive to meiosis II.

4. Set up your answer based on the differences between the two divisions.

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Q5. Based on the image below, which labels represent sister chromatids?

Background

Topic: Chromosome Structure

This question tests your ability to identify sister chromatids, which are identical copies of a chromosome connected by a centromere.

Key Terms:

• Sister chromatids: Two identical DNA molecules joined at the centromere.

• Homologous chromosomes: Chromosomes from each parent with the same genes but possibly different alleles.

Step-by-Step Guidance

1. Identify the two arms of each X-shaped chromosome; these are the sister chromatids.

2. Look for labels pointing to the two halves of each chromosome structure.

3. Recall that sister chromatids are within the same chromosome, not between homologs.

4. Determine which labels correspond to the two chromatids of a single chromosome.

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Q6. Based on the image below, the structure labeled “5” is a chromatid. True or False?

Background

Topic: Chromosome Structure

This question tests your ability to identify chromatids in a chromosome diagram.

Key Terms:

• Chromatid: One of two identical halves of a replicated chromosome.

Step-by-Step Guidance

1. Locate label “5” in the diagram and determine if it points to one half of the X-shaped chromosome.

2. Recall that each half of the X is a chromatid.

3. Check if label “5” is pointing to a single chromatid or another structure.

4. Set up your answer based on the definition of a chromatid.

Try solving on your own before revealing the answer!