Biology: Mitosis and Meiosis
15 practice questions · 15 flashcards · made from study notes
Terms in this set (15)
- What are the three main reasons cells divide?
- Growth, repair, and reproduction.
- Before cell division, a cell passes through interphase. Name its three stages.
- G1 (growth), S phase (DNA replication), and G2 (preparation for division).
- During the S phase of interphase, what crucial event occurs regarding DNA?
- DNA replication, resulting in each chromosome consisting of two identical sister chromatids joined at a centromere.
- Mitosis produces two genetically identical ___ daughter cells and is used for growth and repair of body (somatic) cells.
- diploid
- Describe the key events that occur during prophase of mitosis.
- Chromosomes condense, the nuclear envelope breaks down, and the spindle begins to form.
- In metaphase of mitosis, chromosomes line up single file along the ___.
- metaphase plate
- How does cytokinesis differ between animal and plant cells?
- Animal cells form a cleavage furrow, while plant cells build a cell plate.
- Meiosis produces four genetically different ___ cells called gametes.
- haploid
- Define crossing over in the context of meiosis.
- The exchange of segments between non-sister chromatids of homologous chromosomes, creating new combinations of alleles.
- What is independent assortment and when does it occur in meiosis I?
- The random orientation of homologous pairs as they line up at the metaphase plate in metaphase I.
- Which stage of meiosis is known as the reduction division, and why?
- Meiosis I, because it takes the cell from diploid to haploid as homologous chromosomes separate.
- Name the three main sources of genetic variation from meiosis and sexual reproduction.
- Crossing over, independent assortment, and random fertilization.
- What is nondisjunction?
- Errors in separation where homologous chromosomes or sister chromatids fail to separate during meiosis.
- What condition can result from the fertilization of a gamete with an extra chromosome due to nondisjunction?
- Trisomy, such as trisomy 21 (Down syndrome).
- What does the G1 checkpoint in the cell cycle primarily check for?
- Cell size and DNA damage.
Practice questions (15)
1.What is the correct sequence of the stages of mitosis after interphase?
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Answer: Prophase, metaphase, anaphase, telophase
This question assesses the student's ability to recall the chronological order of the four main stages of mitosis. Knowing the sequence is a foundational requirement for describing the process of cell division accurately.
2.In the stage of mitosis known as anaphase, the sister chromatids that were joined at a centromere are pulled apart to opposite poles of the cell.
- ATrue
- BFalse
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Answer: True
This question tests the student's comprehension of the specific event that defines anaphase. The separation of sister chromatids is a critical step that ensures each new daughter cell receives a complete set of chromosomes.
3.Imagine you are a scientist observing a dividing cell. You notice that the chromosomes have condensed and are visible, the nuclear envelope has broken down, but the chromosomes have not yet lined up in the middle of the cell. What stage of mitosis are you observing?
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Answer: Prophase
This question asks students to apply their knowledge of the stages of mitosis to a descriptive scenario, encouraging them to think like a biologist. It requires them to identify a stage based on its key observable events, reflecting on the visual characteristics of the process.
4.In mitosis, sister chromatids separate during anaphase. In meiosis, a similar separation of sister chromatids occurs, but at a different stage. Which stage of meiosis is most like anaphase of mitosis?
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Answer: Anaphase II
This question challenges students to compare the specific mechanics of the two processes. It requires them to know that meiosis II is structurally similar to mitosis and to identify the specific phase where sister chromatid separation occurs, reinforcing the distinction between meiosis I (separation of homologous chromosomes) and meiosis II.
5.The statement 'Meiosis I is the reduction division' means that the cell's chromosome number is halved. How does the alignment of chromosomes in metaphase I of meiosis differ from their alignment in metaphase of mitosis to make this reduction possible?
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Answer: In metaphase I of meiosis, homologous chromosomes pair up and line up at the metaphase plate. In metaphase of mitosis, individual chromosomes line up single file. This pairing in meiosis I allows the homologous chromosomes (each still made of two sister chromatids) to be separated, which halves the chromosome number.
This question asks for a deeper analysis of the 'how' and 'why' behind the reductional nature of Meiosis I. It forces students to connect the arrangement of chromosomes at the metaphase plate directly to the outcome of the division, contrasting it with the arrangement in mitosis to highlight the key mechanistic difference.
6.Both mitosis and meiosis produce new cells, but only meiosis introduces genetic variation. Which two events, unique to meiosis, are the primary sources of this variation?
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Answer: Crossing over and independent assortment.
This question focuses on a key functional difference between mitosis and meiosis. Mitosis is about creating identical copies, while meiosis is about creating genetic diversity for sexual reproduction. Identifying the specific mechanisms (crossing over and independent assortment) that generate this diversity is crucial for understanding the purpose of meiosis.
7.During prophase I of meiosis, homologous chromosomes pair up and exchange segments between non-sister chromatids. What is this process called and what is its primary significance?
- AIndependent assortment, which shuffles homologous chromosomes.
- BCytokinesis, which divides the cytoplasm to form new cells.
- CCrossing over, which creates new combinations of alleles on a chromosome.
- DNondisjunction, which causes errors in chromosome number.
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Answer: Crossing over, which creates new combinations of alleles on a chromosome.
This question directly tests the student's understanding of crossing over, a key mechanism for genetic variation introduced in the text. It requires them to recall both the term and its function.
8.The random orientation of homologous chromosome pairs at the metaphase plate during meiosis I is known as independent assortment. True or False: This process contributes to genetic variation by creating different combinations of chromosomes in the resulting gametes.
- ATrue
- BFalse
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Answer: True
This question assesses the student's comprehension of independent assortment and its role in generating genetic diversity. It connects the definition of the process to its outcome.
9.Besides crossing over, what is the other mechanism during meiosis I that shuffles existing chromosomes into new combinations, contributing to genetic diversity?
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Answer: Independent assortment
This question requires the student to recall the two main sources of genetic variation that occur during meiosis I as described in the text, differentiating them from other processes.
10.If a cell has a mutation in the gene for p53, a tumor suppressor, which checkpoint would be most affected, and what would be the likely result?
- AThe G1 checkpoint; the cell might divide even if it has damaged DNA.
- BThe M checkpoint; sister chromatids would fail to separate.
- CThe G2 checkpoint; the cell would be stuck in the S phase.
- DThe S phase checkpoint; DNA replication would not be initiated.
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Answer: The G1 checkpoint; the cell might divide even if it has damaged DNA.
This question directly tests the student's understanding of the role of specific checkpoint proteins mentioned in the text (p53) and the consequences of their failure. The p53 protein is a key regulator of the G1 checkpoint, which assesses DNA damage. A mutation would allow cells with damaged DNA to proceed through the cycle, a hallmark of cancer development.
11.True or False: A failure at the spindle (M) checkpoint, which ensures all chromosomes are attached to the spindle, could directly lead to aneuploidy (an abnormal number of chromosomes) but is not considered a cause of uncontrolled cell division like cancer.
- ATrue
- BFalse
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Answer: False
This question challenges the student to connect different types of cell cycle errors. While failure at the M checkpoint is a classic cause of aneuploidy (like trisomy), the text explicitly links mutations in genes controlling *any* checkpoint to cancer. A faulty M checkpoint leads to genetic instability, which is a key characteristic of cancer cells, promoting uncontrolled division.
12.Explain how a failure of the G2 checkpoint, which confirms that DNA replication is complete, could contribute to the development of cancer.
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Answer: If the G2 checkpoint fails, a cell might enter mitosis before its DNA has been fully and correctly copied. This can lead to daughter cells with incomplete or damaged chromosomes. This genetic instability can cause mutations in other genes that control cell growth, leading to uncontrolled cell division and the formation of a tumor.
This question requires students to apply their knowledge of the G2 checkpoint's function to a disease context. It prompts them to reason through the chain of events: a failed checkpoint leads to errors in cell division, which causes genetic instability, which in turn can result in the uncontrolled growth characteristic of cancer. This reinforces the connection between molecular control and disease.
13.The process of cytokinesis, where the cytoplasm divides, differs between plant and animal cells. What structure forms in a plant cell to complete this division that is not found in an animal cell?
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Answer: A cell plate forms in a plant cell, which develops into a new cell wall separating the two daughter cells. Animal cells, lacking a cell wall, form a cleavage furrow instead.
This question tests the student's understanding of a specific difference in cell division between plant and animal cells mentioned in the text. It requires them to recall the specific terminology (cell plate) and its function, reinforcing key biological distinctions.
14.In humans, independent assortment of chromosomes during meiosis I can create about 8.4 million different combinations. What would happen to this number if a person had one fewer pair of homologous chromosomes (i.e., 22 pairs instead of 23)?
- AThe number of combinations would remain the same.
- BThe number of combinations would decrease slightly, by 2.
- CThe number of combinations would be squared.
- DThe number of combinations would be halved.
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Answer: The number of combinations would be halved.
This question challenges students to apply the mathematical principle (2^n) behind independent assortment. By understanding that the number of pairs (n) is the exponent, they can deduce that reducing n by 1 (from 2^23 to 2^22) halves the total number of combinations, demonstrating a deeper understanding of the mechanism's quantitative impact on genetic variation.
15.Nondisjunction is an error where chromosomes fail to separate correctly during meiosis, leading to gametes with an incorrect number of chromosomes. Consider your own family or traits you've observed in others. Can you think of any genetic conditions or traits that might be less visible or obvious than something like trisomy 21 (Down syndrome), and reflect on why some genetic variations have more pronounced effects than others?
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Answer: Some less visible conditions caused by nondisjunction involve sex chromosomes, like Klinefelter syndrome (XXY) or Turner syndrome (XO), which may not be diagnosed until puberty. The reason some variations have more pronounced effects relates to which chromosome is affected and how many genes it carries. Chromosome 21 is small, so an extra copy is more survivable than an extra copy of a larger chromosome, which would likely be lethal.
This question encourages reflection by connecting the abstract concept of nondisjunction to real-world human genetics. It prompts students to think beyond the textbook example of Down syndrome and consider the spectrum of effects that genetic variations can have, fostering a more nuanced understanding of genotype-phenotype relationships.
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