Concepts Klug, of Genetics 8/e CHAPTER 2 MEDIA REVIEW QUESTIONS 1. Which organelle is responsible for generating cellular energy in the form of ATP? HINT: This organelle is found in both plant and animal cells. a. Nucleus Incorrect. The nucleus contains the genetic material, DNA, and is not involved in energy production. 2.1 Cell Structure Is Closely Tied to Genetic Function (p. 18) b. Chloroplast Incorrect. This organelle is found only in plant cells and is associated with photosynthesis. 2.1 Cell Structure Is Closely Tied to Genetic Function (p. 18) c.Mitochondrion Correct. The mitochondrion is the site where the chemical energy in glucose and other molecules is harvested to produce ATP. 2.1 Cell Structure Is Closely Tied to Genetic Function (p. 18) d. Endoplasmic reticulum Incorrect. The endoplasmic reticulum is a membranous structure that is involved in the production of lipids or proteins. 2.1 Cell Structure Is Closely Tied to Genetic Function (p. 18) Which of the following cell structures are directly involved in protein synthesis? HINT: Where does translation take place? a. Smooth endoplasmic reticulum and the nucleus Incorrect. The smooth endoplasmic reticulum is involved in lipid synthesis. 2.1 Cell Structure Is Closely Tied to Genetic Function (p. 18) b. Chloroplasts and mitochondria Incorrect. Neither chloroplasts nor mitochondria are involved in protein synthesis. 2.1 Cell Structure Is Closely Tied to Genetic Function (p. 18) c.Nucleus and plasma membrane Incorrect. The plasma membrane encloses the cell and is not involved in protein synthesis. 2.1 Cell Structure Is Closely Tied to Genetic Function (p. 18) d. Rough endoplasmic reticulum and ribosomes Correct. Ribosomes are the sites of protein translation, and some ribosomes attach to the rough endoplasmic reticulum. 2.1 Cell Structure Is Closely Tied to Genetic Function (p. 18) True or false? A telocentric chromosome has its centromere located very close to, but not on, the end of the chromosome.
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HINT: The position of the centromere determines the shape of the chromosome during its migration to one side of a cell during anaphase. False. An acrocentric chromosome has its centromere located very close to the end of the chromosome; a telocentric centromere is located at the very end of the chromosome. 2.2 In Diploid Organisms, Chromosomes Exist in Homologous Pairs (p. 20) 4. Cells that are metabolically active but are not destined to proliferate are said to be in HINT: Cells in this phase are said to be quiescent because they have exited the cell cycle. a. S phase Incorrect. S phase is the phase during which DNA replication takes place. 2.3 Mitosis Partitions Chromosomes in Dividing Cells (p. 23) b. G0 phase Correct. When cells are in G0, they have withdrawn from the cell cycle and do not proliferate. 2.3 Mitosis Partitions Chromosomes in Dividing Cells (p. 23) c.G1 phase Incorrect. G1 phase is the phase during which cells prepare to replicate their DNA. 2.3 Mitosis Partitions Chromosomes in Dividing Cells (p. 23) d. G2 phase Incorrect. G2 phase is the phase during which cells get bigger and prepare to divide. 2.3 Mitosis Partitions Chromosomes in Dividing Cells (p. 23) When is DNA duplicated for cell division? HINT: Cells must duplicate their DNA before they divide. a. During the S period of interphase Correct. Cells duplicate their DNA during S phase of the cell cycle. 2.3 Mitosis Partitions Chromosomes in Dividing Cells (p. 23) b. During metaphase of mitosis and meiosis Incorrect. DNA is already duplicated by metaphase of both mitosis and meiosis. 2.3 Mitosis Partitions Chromosomes in Dividing Cells (p. 23) c.During prophase of mitosis and meiosis Incorrect. DNA is already duplicated by prophase of both mitosis and meiosis. 2.3 Mitosis Partitions Chromosomes in Dividing Cells (p. 23) d. During G1 and G2 of interphase Incorrect. DNA is duplicated after G1 and before G2 of the cell cycle. 2.3 Mitosis Partitions Chromosomes in Dividing Cells (p. 23)
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True or false? The primary differences observed for plant cell mitosis relative to animal cell mitosis occur during telophase. HINT: The plant cell wall poses a special problem during cytokinesis. True. During telophase, plant cells synthesize a cell plate that is laid down across the region of the metaphase plate. 2.3 Mitosis Partitions Chromosomes in Dividing Cells (p. 23) Which of the following statements about meiosis is true? HINT: The goal of meiosis is to create cells necessary for reproduction. a. The chromosome number is doubled. Incorrect. The chromosome number is doubled prior to meiosis during interphase. Therefore, DNA replication is not a part of meiosis. 2.4 Meiosis Reduces the Chromosome Number from Diploid to Haploid in Germ Cells and Spores (p. 27) b. Two identical cells are produced. Incorrect. Four genetically unique cells are produced during meiosis. Two identical cells are produced during mitosis. 2.4 Meiosis Reduces the Chromosome Number from Diploid to Haploid in Germ Cells and Spores (p. 27) c.The chromosome number stays the same. Incorrect. If this occurred during the formation of the sex cells, the next generation would have twice as many chromosomes. 2.4 Meiosis Reduces the Chromosome Number from Diploid to Haploid in Germ Cells and Spores (p. 27) d. The chromosome number is reduced by onehalf. Correct. Meiosis produces gametes, which fuse to form zygotes that have the original number of chromosomes present before meiosis. This can happen only if gametes contain onehalf the number of chromosomes as the zygote. 2.4 Meiosis Reduces the Chromosome Number from Diploid to Haploid in Germ Cells and Spores (p. 27) Which of the following statements describes leptonema? HINT: Leptonema is the very first stage of prophase I. a. It is the time of most intimate pairing, called synapsis. Incorrect. Synapsis occurs during pachynema of prophase I. 2.4 Meiosis Reduces the Chromosome Number from Diploid to Haploid in Germ Cells and Spores (p. 27) b. It is the period when the chromatin begins to condense.
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Correct. Leptonema is the first portion of prophase I, when the diffuse chromatin material in the nucleus begins to condense and chromosomes first become visible under a microscope. 2.4 Meiosis Reduces the Chromosome Number from Diploid to Haploid in Germ Cells and Spores (p. 27) c.It corresponds to the first or reductional division in meiosis. Incorrect. Chromatids do not divide during prophase I. 2.4 Meiosis Reduces the Chromosome Number from Diploid to Haploid in Germ Cells and Spores (p. 27) d. It is the time when crossing over takes place, although this will not be apparent until later stages. Incorrect. Crossing over occurs during pachynema of prophase I. 2.4 Meiosis Reduces the Chromosome Number from Diploid to Haploid in Germ Cells and Spores (p. 27) 9. Crossing over refers to HINT: This event produces new gene combinations. a. The random segregation of dyads in metaphase I of meiosis Incorrect. The separation of dyads occurs during the first reductional meiotic division. 2.4 Meiosis Reduces the Chromosome Number from Diploid to Haploid in Germ Cells and Spores (p. 27) b. The formation of lateral elements between paired homologs during zygonema Incorrect. This event describes the formation of the synaptonemal complex, which leads to crossing over of the paired homologs. 2.4 Meiosis Reduces the Chromosome Number from Diploid to Haploid in Germ Cells and Spores (p. 27) c.The onset of homology search in the leptonene stage of meiosis I Incorrect. This event precedes and is essential to the initial pairing of homologs during meiosis. 2.4 Meiosis Reduces the Chromosome Number from Diploid to Haploid in Germ Cells and Spores (p. 27) d. Genetic exchange between nonsister chromatids during meiosis Correct. Although the chiasmata observed during diplonema signal crossover events, the actual exchange of genetic material likely takes place during the preceding pachytene stage when homologs are most closely paired. 2.4 Meiosis Reduces the Chromosome Number from Diploid to Haploid in Germ Cells and Spores (p. 27) In humans, what is a fundamental difference between the production of female gametes and male gametes? HINT: Consider the number of male and female gametes formed during meiosis. a. Male gametes are haploid, while female gametes are diploid.
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Incorrect. Both male and female gametes are haploid. 2.5 The Development of Gametes Varies during Spermatogenesis and Oogenesis (p. 31) b. Male gametes require four meiotic divisions, while female gametes require only two. Incorrect. All meiosis consists of two divisions. 2.5 The Development of Gametes Varies during Spermatogenesis and Oogenesis (p. 31) c.The production of female gametes involves an unequal division of cytoplasm. Correct. During the production of female gametes, one daughter cell contains most of the cytoplasm and one polar body contains only a small amount of cytoplasm. Thus, female gametes are 400 times larger than sperm. 2.5 The Development of Gametes Varies during Spermatogenesis and Oogenesis (p. 31) d. Female gametes are haploid, whereas male gametes are diploid. Incorrect. Both male and female gametes are haploid. 2.5 The Development of Gametes Varies during Spermatogenesis and Oogenesis (p. 31) 11. Which stage of meiosis enhances genetic variability among gametes? HINT: At which stage does crossing over occur? a. Telophase Incorrect. Chromosomes move to the poles of the cell during this stage, but no variation is created. 2.6 Meiosis Is Critical to the Successful Sexual Reproduction of All Diploid Organisms (p. 32) b. Prophase I Correct. Crossing over and recombination occur during prophase I. 2.6 Meiosis Is Critical to the Successful Sexual Reproduction of All Diploid Organisms (p. 32) c.Anaphase I Incorrect. Gamete composition depends on which of the two homologs is pulled to each daughter cell. 2.6 Meiosis Is Critical to the Successful Sexual Reproduction of All Diploid Organisms (p. 32) d. Anaphase II Incorrect. Gamete composition depends on which of the two sister chromatids is pulled to each daughter cell. 2.6 Meiosis Is Critical to the Successful Sexual Reproduction of All Diploid Organisms (p. 32) During which stage of the cell cycle are individual chromosomes not visible within cells? HINT: What form do chromosomes take interphase? during a. Anaphase
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Incorrect. Chromosomes are visible as rodlike structures during most of mitosis. 2.7 Electron Microscopy Has Revealed the Cytological Nature of Mitotic and Meiotic Chromosomes (p. 33) b. Telophase Incorrect. Chromosomes are visible as rodlike structures during most of mitosis. 2.7 Electron Microscopy Has Revealed the Cytological Nature of Mitotic and Meiotic Chromosomes (p. 33) c.S phase Correct. Chromosomes are visible during most of mitosis but are present as diffuse chromatin during interphase. S phase (corresponding to the period when DNA is duplicated) is the only choice that is in interphase. 2.7 Electron Microscopy Has Revealed the Cytological Nature of Mitotic and Meiotic Chromosomes (p. 33) d. Metaphase Incorrect. Chromosomes are visible as rodlike structures during most of mitosis. 2.7 Electron Microscopy Has Revealed the Cytological Nature of Mitotic and Meiotic Chromosomes (p. 33) 13. Which of the following statements about cell division is false? HINT: Compare the end products of mitosis and meiosis. a. Meiosis eventually results in the formation of gametes. Incorrect. This statement is true; meiosis only occurs in the gonads where sperm and eggs are produced. b. In mitosis the daughter cells are haploid, whereas in meiosis the daughter cells are diploid. Correct. This statement is false. Meiosis produces haploid gametes, mitosis produces diploid somatic cells. c.In meiosis, but not mitosis, there is a reduction in the amount of genetic material in the daughter cells. Incorrect. This statement is true; meiosis, not mitosis, is described as a reduction division. d. In mitosis, but not meiosis, the daughter cells are identical copies of the mother cell. Incorrect. This statement is true; in meiosis, gametes with completely new combinations of alleles are produced. Which of the following statements about homologous chromosomes is true? HINT: Homologous chromosomes are copies of the same type of chromosome.
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a. Homologous chromosomes pair up and undergo recombination during prophase of mitosis. Incorrect. Crossing over and recombination occur only during meiosis. b. They contain all of the same genes but not necessarily the same alleles. Correct. One copy may contain the allele for blue eyes, the other for brown eyes; both are the eyecolor genes, but they may be different alleles. c.In each cell, there are two pairs of homologous chromosomes--one pair from each parent. Incorrect. Each parent contributes a single copy, not a pair, for each chromosome. d. They are identical sequences of base pairs. Incorrect. Homologous chromosomes come from different parents and so may carry different alleles. 15. Checkpoints are points between phases of the cell cycle at which a cell determines whether all the requirements necessary for each phase of the cell cycle have been properly satisfied. For example, because a cell with damaged DNA can lead to cancer if it is allowed to divide, a cell with damaged DNA usually arrests the cell cycle until the damage can be repaired. At which phase of the cell cycle would a cell normally check for the integrity of its DNA? HINT: DNA is usually inspected for damage prior to replication and for the presence of sister chromatids after replication is complete. a. M phase Incorrect. DNA damage is checked before cell division begins. b. G1/S phase Incorrect. DNA damage is checked before and also after replication. c.G2/S phase Incorrect. DNA damage is checked both before and after replication. d. G1/S and G2/M phases Correct. The G1/S checkpoint monitors cell size and checks for damaged DNA. The G2/M checkpoint monitors whether DNA replication and repair to any damaged DNA has been completed. Both are likely to arrest the cell cycle if they detect damaged DNA. How many tetrads are found in meiotic prophase in an organism with a diploid number of 12? HINT: Tetrads are formed when homologous chromosomes synapse. a. 6
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Correct. Each set of homologous chromosomes will pair to form the tetrads. If the diploid number is 12, there are actually 6 different chromosomes, which will be replicated and then pair up to form the tetrads. b. 18 Incorrect. Each set of homologous chromosomes will pair to form the tetrads. If the diploid number is 12, there are two copies of each of 6 different chromosomes. c.24 Incorrect. Each set of homologous chromosomes will pair to form the tetrads. If the diploid number is 12, there are two copies of 6 different chromosomes. d. 12 Incorrect. The diploid number is 12, which means that there are two copies of 6 different chromosomes that will replicate and synapse to form the tetrads. The number of tetrads will equal the haploid number. 16. Humans are diploid and have two copies each of 23 chromosomes. How many chromatids would be present in a cell during prophase I of meiosis? HINT: Chromosomes are replicated before meiosis begins. a. 46 Incorrect. Each chromosome has replicated prior to meiosis. b. 69 Incorrect. Every chromosome has a homolog. Thus, the total number of chromosomes must always be an even number. c.23 Incorrect. There are 23 pairs of chromosomes in each cell prior to replication. d. 92 Correct. Each of the 46 chromosomes has replicated at this point, and each chromosome is composed of 2 chromatids. In an organism with a diploid number of 4, how many chromatids are aligned in the equatorial plane of a cell during metaphase II? HINT: If meiosis I is a reductional division, how many chromosomes are left in each cell if the original cell had 4? How many chromatids? a. 2 Incorrect. Meiosis I reduces the chromosome number from 4 to 2, so each cell has 2 replicated chromosomes. b. 4 Correct. Meiosis I reduces the chromosome number from 4 to 2, so each replicated chromosome has 2 chromatids each.
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c.6 Incorrect. Meiosis I reduces the chromosome number from 4 to 2, so each cell has 2 replicated chromosomes. d. 8 Incorrect. Meiosis I reduces the chromosome number from 4 to 2, so each cell has 2 replicated chromosomes. 18. How does recombination produce gametes of almost infinite variety? HINT: Recombination, also called crossing over, produces the tetrads observable during prophase I of meiosis. a. By causing exchange of alleles between homologous chromosomes Correct. Chromosomes with unique combinations of alleles are created by exchanging random alleles between homologs. b. By causing sister chromatids to exchange genetic material with each other Incorrect. Sister chromatids are the result of replication and thus are identical to each other. c.By causing segregation of the different homologs to different gametes Incorrect. Segregation does lead to variation, but it does not result from recombination. d. By inducing beneficial mutations in gametophytes Incorrect. Recombination does not induce mutation. Why do the chromosomes of a mitotic cell look like X's under a microscope if they are linear strands? HINT: Chromosomes are visible only during cell division after they've replicated. a. When chromatin coils, it takes on an Xshape. Incorrect. Chromatin contains a linear DNA molecule. b. Each linear strand has replicated during interphase. Correct. The Xshaped structure is actually two identical strands of DNA (sister chromatids) linked at the centromere. c.Homologous chromosomes join as tetrads during mitosis. Incorrect. Tetrads form during meiosis only. d. Chromosomes are always Xshaped because the maternal and paternal contributions are linked together at the centromere. Incorrect. Maternal and paternal chromosomes are separate entities. During which stage can cells either exit the cell cycle or become committed to completing the cell cycle? HINT: Cells that withdraw from the cell cycle are said to enter the G0 stage.
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a. G2 Incorrect. Cells that have entered G2 are committed to the cell cycle. b. M Incorrect. Cells that have entered M are about to undergo mitosis. c.S Incorrect. Cells that have entered S are replicating their DNA and are committed to the cell cycle. d. G1 Correct. Cells can exit the cell cycle and enter G0 or be committed to initiate DNA synthesis late in G1. 21. True or false? A dyad is composed of two homologous chromosomes joined at a common centromere. HINT: One chromosome in a homologous pair is inherited paternally and the other is inherited maternally. False. A dyad is composed of two sister chromatids joined at a common centromere. True or false? A tetrad is composed of one pair of homologous chromosomes at synapsis of prophase I. HINT: Tetrads contain two pairs of sister chromatids. True. Chromosomes are duplicated during interphase; at synapsis of prophase I, one chromosome (with two chromatids) in a tetrad is paternally inherited while the other is maternally inherited. A cell has 16 chromosomes. How many chromosomes would its daughter cells have after meiosis? HINT: Chromosomes separate twice during meiosis. a. 4 Incorrect. Meiosis reduces the number of chromosomes passed on to daughter cells by onehalf. b. 8 Correct. Meiosis reduces the number of chromosomes passed on to daughter cells by onehalf. c.16 Incorrect. This would be the chromosome number if the cell underwent mitosis, which produces daughter cells with the same number of chromosomes as the parent. d. 32
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Incorrect. Meiosis reduces the number of chromosomes passed on to daughter cells by onehalf. 24. When do sister chromatids separate during meiosis? HINT: Compare the divisions that occur during meiosis I and meiosis II. a. Metaphase I Incorrect. Tetrads line up along the equatorial plane during metaphase I. b. Metaphase II Incorrect. Dyads line up along the equatorial plane during metaphase II. c.Anaphase I Incorrect. Homologous chromosomes separate during anaphase I. d. Anaphase II Correct. Sister chromatids from each dyad separate during anaphase II. Which condition is evaluated at the G2/M checkpoint? HINT: Consider the order of the stages of the cell cycle. a. Proper spindle formation Incorrect. A cell checks for proper spindle formation at the M checkpoint. b. Precise replication of DNA Correct. A cell checks for precise replication of DNA at the G2/M checkpoint. c.Adequate cell size Incorrect. A cell checks for adequate cell size at the G1/S checkpoint. d. Proper spindle assembly Incorrect. A cell checks for proper spindle assembly at the M checkpoint.
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