Spindle microtubules disintegrate. Briefly describe how the chromosomes move toward the spindle poles during anaphase. Solution: Due to the actions of the microtubule subunits attached to the kinetochores of the chromosome and motor proteins e. The spindle fibers are composed of tubulin protein subunits. In the mitotic cell cycle, the genetic material is precisely copied and mitosis ensures that the identical copies of the genetic material are separated accurately into the new daughter cells, resulting in two cells containing the same genetic information.
In other words, the cells have genomes identical to each other and to the mother cell. Why are the two cells produced by the cell cycle genetically identical?
Solution: The two cells are genetically identical because during S phase an exact copy of each DNA molecule was created. These exact copies give rise to the two identical sister chromatids. Mitosis ensures that each new cell receives one of the two identical sister chromatids. Thus, the newly formed cells will contain identical daughter chromosomes. What are the stages of meiosis and what major events take place in each stage? Solution: Meiosis I:.
Separation of homologous chromosomes Prophase I: The chromosomes condense and homologous pairs of chromosomes undergo synapsis. While the chromosomes are synapsed, crossing over occurs. The nuclear membrane disintegrates and the meiotic spindle begins to form. Metaphase I: The homologous pairs of chromosomes line up on the equatorial plane of the metaphase plate. Anaphase I: Homologous chromosomes separate and move to opposite poles of the cell.
Each chromosome possesses two sister chromatids. Telophase I: The separated homologous chromosomes reach the spindle poles and are at opposite ends of the cell. Meiosis I is followed by cytokinesis, resulting in the division of the cytoplasm and the production of two haploid cells. These cells may skip directly into meiosis II or enter interkinesis, where the nuclear envelope reforms and the spindle fibers break down.
Meiosis II: Separation of sister chromatids Prophase II: Chromosomes condense, the nuclear envelope breaks down, and the spindle fibers form. Metaphase II: Chromosomes line up at the equatorial plane of the metaphase plate. Anaphase II: The centromeres split, which results in the separation of sister chromatids.
Telophase II: The daughter chromosomes arrive at the poles of the spindle. The nuclear envelope reforms, and the spindle fibers break down. Following meiosis II, cytokinesis takes place. What are the major results of meiosis? Solution: Meiosis involves two cell divisions, thus producing four new cells in many species. The chromosome number of a haploid cell produced by meiosis I haploid is half the chromosome number of the original diploid cell.
Finally, the cells produced by meiosis are genetically different from the original cell and genetically different from each other. What two processes unique to meiosis are responsible for genetic variation? At what point in meiosis do these processes take place?
Solution: 1 Crossing over, which begins during the zygotene stage of prophase I and is completed near the end of prophase I. The arrangement for separation is determined by the random alignment of homologs in metaphase I.
How does anaphase I of meiosis differ from anaphase of mitosis? Solution: In anaphase I of meiosis, homologous chromosomes separate whereas in anaphase of mitosis the sister chromatids separate. Briefly explain why sister chromatids remain together in anaphase I but separate in anaphase II of meiosis. Solution: In meiosis, a similar process to mitosis occurs.
Meiosis-specific cohesin complexes different from cohesion proteins in mitosis form at the centromeres of the sister chromatids during the S phase. At the beginning of meiosis, cohesin molecules are also found along the entire length of the chromosome arms assisting in the formation of the synaptonemal complex and holding together the two homologs. During anaphase I of meiosis, the cohesin molecules along the arms are cleaved by activated separase allowing the homologs to separate.
However, the cohesin complexes at the centromeres of the sister chromatids are protected from the action of separase by the protein shugoshin and are unaffected. The result is that sister chromatids remained attached during anaphase I. At the end of metaphase II, the.
Outline the processes of spermatogenesis and oogenesis in animals. Solution: In animals, spermatogenesis occurs in the testes. Primordial diploid germ cells divide mitotically to produce diploid spermatogonia that can either divide repeatedly by mitosis or enter meiosis. A spermatogonium that has entered prophase I of meiosis is called a primary spermatocyte and is diploid.
Upon completion of meiosis I, two haploid cells, called secondary spermatocytes, are produced. Upon completing meiosis II, the secondary spermatocytes produce a total of four haploid spermatids. Female animals produce eggs through the process of oogenesis. Similar to what takes place in spermatogenesis, primordial diploid cells divide mitotically to produce diploid oogonia that can divide repeatedly by mitosis, or enter meiosis. An oogonium that has entered prophase I is called a primary oocyte and is diploid.
Upon completion of meiosis I, the cell divides, but unequally. One of the newly produced haploid cells receives most of the cytoplasm and is called the secondary oocyte. The other haploid cell receives only a small portion of the cytoplasm and is called the first polar body. Ultimately, the secondary oocyte will complete meiosis II and produce two haploid cells. One cell, the ovum, will receive most of the cytoplasm from the secondary oocyte. The smaller haploid cell is called the second polar body.
Typically, the polar bodies disintegrate, and only the ovum is capable of being fertilized. Outline the processes of male gamete formation and female gamete formation in plants. Solution: Plants alternate between a multicellular haploid stage called the gametophyte and a multicellular diploid stage called the sporophyte.
Meiosis in the diploid sporophyte stage of plants produces haploid spores that develop into the gametophyte. The gametophyte produces gametes by mitosis. In flowering plants, the microsporocytes found in the stamen of the flower undergo meiosis to produce four haploid microspores. Each microspore divides by mitosis to produce the pollen grain, or the microgametophyte.
Within the pollen grain are two haploid nuclei. One of the haploid nuclei divides by mitosis to produce two sperm cells.
The other haploid nucleus directs the formation of the pollen tube. Female gamete production in flowering plants takes place within the megagametophyte. Megasporocytes found within the ovary of a flower divide by meiosis to produce four megaspores. Three of the megaspores disintegrate, while the remaining megaspore divides mitotically to produce eight nuclei that form the embryo sac or female gametophyte.
Of the eight nuclei, one will become the egg. What do the two socks of a pair represent in the cell cycle? Solution: The two chromatids of a chromosome b. In the riddle, each blind man buys his own pairs of socks, but the clerk places all the pairs in one bag. Thus, there are two pairs of socks of each color in the bag two black pairs, two blue pairs, two gray pairs, etc.
What do the two pairs four socks in all of each color represent? Solution: The two chromosomes of a homologous pair c. What is the thread that connects the two socks of a pair? Solution: Cohesin d. What is the molecular knife that cuts the thread holding the two socks in a pair together?
Solution: The enzyme separase e. What in the riddle performs the same function as spindle microtubles? Solution: The hands of the two blind men f. What would happen if one man failed to grasp his sock of a particular pair? How does that outcome relate to events in the cell cycle? Solution: If one man failed to grasp his sock, it would be difficult for the knife to cut the string holding them together.
Similarly, if each chromatid is not attached to spindle fibers and pulled in opposite directions, the two chromatids will not separate and both would migrate to the same cell. This cell would have two copies of one chromosome. Section 2.
A cell has a circular chromosome and no nuclear membrane. Its DNA is complexed with some histone proteins. Does this cell belong to a eubacterium, an archaean, or a eukaryote? Explain your reasoning. Solution: This cell is most likely an archaea. The cell is not eukaryotic because it lacks a nuclear membrane and has a single circular chromosome. The cell is not a eubacterium because it has histone proteins, which are present in archaea and eukaryotes but lacking in eubacteria.
A certain species has three pairs of chromosomes: an acrocentric pair, a metacentric pair, and a submetacentric pair. Draw a cell of this species as it would appear in metaphase of mitosis. Examine Figure 2. What type of chromosome metacentric, submetacentric, acrocentric, or telocentric is chromosome 1? What about chromosome 4? Solution: The centromere in chromosome 1 is centrally located, so it is metacentric.
The centromere of chromosome 4 is located between the center and the end of the chromosome, so it is submetacentric. A biologist examines a series of cells and counts cells in interphase, 20 cells in prophase, six cells in prometaphase, two cells in metaphase, seven cells in anaphase, and five cells in telophase.
If the complete cell cycle requires 24 hours, what is the average duration of the M phase in these cells? Of metaphase? Solution: To determine the average duration of M phase in these cells, the proportion of cells in interphase, or in each stage of M phase, should be calculated by dividing the number of cells in each stage by the total number of cells counted. To calculate the time required for a given phase, multiply 24 hours by the proportion of cells at that stage.
This will give the average duration of each stage in hours. The average duration of M phase can be determined by adding up the hours spent in each stage of mitosis. In these cells, M phase lasts 4. The table shows that metaphase requires 0. In what stage of mitosis is the cell illustrated in the chapter-opening figure p.
Solution: In the chapter-opening figure, the sister chromatids within the cell have already separated and have moved apart.
Likely the cell is either in late anaphase or in telophase. A certain species has three pairs of chromosomes: one acrocentric pair and two metacentric pairs. Draw a cell of this species as it would appear in the following stages of meiosis: a. Metaphase I Solution: b.
Anaphase I. Construct a table similar to that in Figure 2. A cell in G1 of interphase has 12 chromosomes. How many chromosomes and DNA molecules will be found per cell when this original cell progresses to the following stages?
Solution: The number of chromosomes and DNA molecules depends on the stage of the cell cycle. Each chromosome contains only one centromere, but after the completion of S phase, and prior to anaphase of mitosis or anaphase II of meiosis, each chromosome will consist of two DNA molecules.
Each chromosome now consists of two DNA molecules. So a cell in G2 will contain 12 chromosomes and 24 DNA molecules. Metaphase I of meiosis. Solution: Neither homologous chromosomes nor sister chromatids have separated by metaphase I of meiosis. Therefore, the chromosome number is 12, and the number of DNA molecules is Anaphase I of meiosis Solution: During anaphase I of meiosis, homologous chromosomes separate and begin moving to opposite ends of the cell.
However, sister chromatids will not separate until anaphase II of meiosis. The number of chromosomes is still 12, and the number of DNA molecules is Anaphase II of meiosis Solution: Homologous chromosomes were separated and migrated to different daughter cells at the completion of meiosis I.
However, in anaphase II of meiosis, sister chromatids separate, resulting in a temporary doubling of the chromosome number in the now haploid daughter cell. The number of chromosomes and the number of DNA molecules present will both be The haploid cells will contain six chromosomes and 12 DNA molecules. After cytokinesis following mitosis Solution: After cytokinesis following mitosis the daughter cells will enter G1. Each cell will contain 12 chromosomes and 12 DNA molecules.
How are the events that take place in spermatogenesis and oogenesis similar? How are they different? Solution: Both spermatogenesis and oogenesis begin similarly in that the diploid primordial cells spermatogonia and oogonia can undergo multiple rounds of mitosis to produce more primordial cells, or both types of cells can enter into meiotic division.
In spermatogenesis, cytokinesis is equal, resulting in haploid cells of similar sizes. Upon completion of meiosis II, four haploid spermatids have been produced for each spermatogonium that began meiosis.
In oogenesis, cytokinesis is unequal. At the completion of meiosis I in oogenesis, a secondary oocyte is produced, which is much larger and contains more cytoplasm than the other haploid cell produced, called the first polar body. At the completion of meiosis II, the secondary oocyte divides, producing the ovum and the second polar body.
Again, the division of the cytoplasm in cytokinesis is unequal, with the ovum receiving most of the cytoplasmic material. Usually, the polar bodies disintegrate, leaving the ovum as the only product of meiosis. All of the following cells, shown in various stages of mitosis and meiosis, come from the same rare species of plant. What is the diploid number of chromosomes in this plant?
Solution: To determine the diploid chromosome number in this plant, the number of centromeres present within a cell that contains homologous pairs of chromosomes must be determined. Remember, each chromosome possesses a single centromere.
The location and presence of a centromere are determined by the attachment of the spindle fibers to the chromosome, which occurs at the centromere in the above diagram.
Only the cell in stage a clearly has homologous pairs of chromosomes. So the diploid chromosome number for cells of this species of plant is six. Give the names of each stage of mitosis or meiosis shown.
Solution: Cell 1 is undergoing anaphase of meiosis I, as indicated by the separation of the homologous pairs of chromosomes. Cell 2 in the diagram contains six chromosomes, the diploid chromosome number for this species. Also in this cell, sister chromatids have separated, resulting in a doubling of the chromosome number within the cell from six to Based on the number of chromosomes, the separation of sister chromatids in this cell must be occurring during anaphase of mitosis. In cell 3 again, sister chromatids are being separated, but the number of chromosomes present in the cell is only six.
This indicates that no homologs are present within the cell, so in this cell the separation of sister chromatids is occurring in anaphase II of meiosis. Give the number of chromosomes and number of DNA molecules per cell present at each stage. Solution: Cell 1, which is in anaphase I of meiosis contains six chromosomes and 12 DNA molecules or sister chromatids. Cell 2 has 12 chromosomes and 12 DNA molecules in anaphase of mitosis. The amount of DNA per cell of a particular species is measured in cells found at various stages of meiosis, and the following amounts are obtained: Amount of DNA per cell in pictograms pg 3.
Match the amounts of DNA above with the corresponding stages of meosis a through f. You may use more than one stage for each amount of DNA. Stage of meiosis a. G1 Solution: 7. Prophase I Solution: The homologous chromosomes are still located within a single cell, and there are two sister chromatids per chromosome. G2 Solution: Following telophase II and cytokinesis Solution: 3.
By the completion of cytokinesis associated with meiosis II, both homologous pairs of chromosomes and sister chromatids have been separated into different daughter cells. Therefore, each daughter cell will contain only one-half the amount of DNA of the original cell in G1. Anaphase I Solution: Metaphase II Solution: 7.
In metaphase II of meiosis, the amount of DNA in each cell is the same as G1 because each chromosome still consists of two DNA molecules two sister chromatids per chromosome. The amount of DNA in the cell will be doubled after the completion of S phase in the cell cycle and prior to cytokinesis in either mitosis or meiosis I. Most figures include text that walks students through the graphical presentation.
Illustrations of experiments reinforce the scientific method by first proposing a hypothesis, then pointing out the methods and results, and ending with a conclusion that reinforces concepts explained in the text. Working through an example, equation, or experiment helps students see concepts in action and reinforces the ideas explained in the text. In the book, I help students develop problem-solving skills in a number of ways.
Worked Problems walk students through each step of a difficult concept. Problem Links spread throughout each chapter point to end-of-chapter problems that students can work to test their understanding of the material they have just read, all with answers in the back of the book so that students can check their results. I provide a wide range of end-of-chapter problems, organized by chapter section and split into Comprehension Questions, Application Questions and Problems, and Challenge Questions.
Some of these questions, marked by a data analysis icon, draw on examples from published, and cited, research articles. This comprehensive and robust online teaching and learning platform incorporates online homework with the e-Book, all instructor and student resources, and powerful gradebook functionality. Students benefit from just-in-time hints and feedback specific to their misconceptions to develop their problem-solving skills, while instructors benefit from automatically graded homework and robust gradebook diagnostics.
NEW Active learning components One of my main goals for this new edition is to provide better resources for active learning. In this edition, I have added Think-Pair-Share questions, which require students to work, and learn, in groups. These questions not only focus on the genetics topics covered in the chapter, but also tie them to genetics in medicine, agriculture, and other aspects of human society.
An online instructor guide provides resources for instructors leading the in-class discussion. Chapter Opening Think-Pair-Share Questions get students to discuss the chapter opening story itself and to connect it with what they know about genetics. End-of-Chapter Think-Pair-Share Questions provide more challenging problem solving for students to work on in groups and encourage them to discuss the bigger-picture aspects of the material they learned in the chapter.
They also allow students to connect the material they have learned to broader genetics topics. Do you like this book?
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