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.
List some similarities and differences between mitosis and meiosis. Which differences do you think are most important and why? Solution: Mitosis A single cell division produces two genetically identical progeny cells.
Chromosome number of progeny cells and the original cell remain the same. Daughter cells and the original cell are genetically identical. No separation of homologous chromosomes or crossing over takes place.
Homologous chromosomes do not synapse. Meiosis Two cell divisions usually result in four progeny cells that are not genetically identical. Daughter cells are haploid and have half the chromosomal complement of the original diploid cell as a result of the separation of homologous pairs during anaphase I.
Crossing over in prophase I and separation of homologous pairs during anaphase I produce daughter cells that are genetically different from each other and from the original cell. Synapsis of homologous chromosomes takes place during prophase I. In metaphase, individual chromosomes line up on the metaphase plate.
In anaphase, sister chromatids separate. In metaphase I, homologous pairs of chromosomes line up on the metaphase plate. Individual chromosomes line up in metaphase II. In anaphase I, homologous chromosomes separate. Separation of sister chromatids takes place in anaphase II.
Division of the cell occurs in both meiosis I and II. The most important difference is that mitosis produces cells genetically identical to each other and to the original cell, resulting in the orderly passage of information from one cell to its progeny. In contrast, by producing progeny that do not contain pairs of homologous chromosomes, meiosis results in the reduction of chromosome number from the original cell. Meiosis also allows for genetic variation through crossing over and the random assortment of homologous chromosomes.
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 protection of the cohesin molecules at the centromeres is lost, and the separase proteins can now cleave the cohesin complex, which allows the sister chromatids to separate.
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 of the pairs into 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.
In the cell cycle, what is the thread that connects the two socks of a pair? Solution: Cohesin d. In the cell cycle, 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 fibers?
Solution: The hands of the two blind men f. What would happen if one man failed to grasp his sock of a particular pair and how does it 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. 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.
How would each of the following events affect the outcome of mitosis or meiosis? Mitotic cohesin fails to form early in mitosis. Solution: Cohesin is necessary to hold the sister chromatids together until anaphase of mitosis.
If cohesin fails to form early in mitosis, the sister chromatids could separate prior to. The result would be improper segregation of chromosomes to daughter cells. Shugoshin is absent during meiosis. Solution: Shugoshin protects cohesin proteins from degradation at the centromere during meiosis I. Cohesin at the arms of the homologous chromosomes is not protected by shugoshin and is broken in anaphase I, allowing for the two homologs to separate. If shugosin is absent during meiosis, then the cohesin at the centromere may be broken, allowing for the separation of sister chromatids along with the homologs during anaphase I, leading to improper segregation of chromosomes to daughter cells.
Shugoshin does not break down after anaphase I of meiosis. Solution: If shugoshin is not broken down, then the cohesins at the centromere will remain protected from degradation. The intact cohesins will prevent the sister chromatids from separating during anaphase II of meiosis, resulting in an improper separation of sister chromatids and daughter cells with too many or too few chromosomes. Separase is defective.
Solution: Homologous chromosomes and sister chromatids would not separate in meiosis and mitosis, resulting in some cells that have too few chromosomes and some cells that have too many chromosomes. A cell in prophase II of meiosis contains 12 chromosomes.
How many chromosomes would be present in a cell from the same organism if it were in prophase of mitosis? Prophase I of meiosis? Solution: A cell in prophase II of meiosis will contain the haploid number of chromosomes. For this organism, 12 chromosomes represent the haploid chromosome number of a cell, or one complete set of chromosomes.
A cell from the same organism that is undergoing prophase of mitosis would contain a diploid number of chromosomes, or two complete sets of chromosomes, which means that homologous pairs of chromosomes are present. So a cell in this stage should contain 24 chromosomes. Homologous pairs of chromosomes have not been separated by prophase I of meiosis. During this stage, a cell of this organism will contain 24 chromosomes. A cell has eight chromosomes in G1 of interphase.
Draw a picture of this cell with its chromosomes at the following stages. Indicate how many DNA molecules are present at each stage. Solution: a. Metaphase of mitosis. The fruit fly Drosophila melanogaster has four pairs of chromosomes, whereas the house fly Musca domestica has six pairs of chromosomes.
In which species would you expect to see more genetic variation among the progeny of a cross? Explain your answer. Solution: The progeny of an organism whose cells contain more homologous pairs of chromosomes should be expected to exhibit more variation.
The number of different combinations of chromosomes that are possible in the gametes is 2n, where n is equal to the number of homologous pairs of chromosomes. Allele M is located on the long arm of chromosome Ia, and allele m is located at the same position on chromosome Ib. Allele P is located on the short arm of chromosome Ia, and allele p is located at the same position on chromosome Ib. Allele R is located on chromosome IIa and allele r is located at the same position on chromosome IIb.
Draw these chromosomes, identifying genes M, m, P, p, R, and r, as they might appear in metaphase I of meiosis. Assume that there is no crossing over. Solution: M M. A horse has 64 chromosomes and a donkey has 62 chromosomes. A cross between a female horse and a male donkey produces a mule, which is usually sterile. How many chromosomes does a mule have? Can you think of any reasons for the fact that most mules are sterile?
Solution: The haploid egg produced by the female horse contains 32 chromosomes. The haploid sperm produced by the male donkey contains 31 chromosomes. The union of the horse and donkey gametes will produce a zygote containing 63 chromosomes. From the zygote, the adult mule will develop and will contain cells with a chromosome number of During the production of gametes by meiosis when pairing and separation of homologous chromosomes occurs, the odd chromosome will be unable to pair up.
If improper synapsis or no synapsis occurs during prophase I, this will result in faulty segregation of chromosomes to the daughter cells produced at the conclusion of meiosis I.
This leads to gametes that have abnormal numbers of chromosomes. When these abnormal gametes unite, the resulting zygote has an abnormal number of chromosomes and will be nonviable. How many chromosomes and DNA molecules will be present in the following types of horse cells? Solution: Cell type a. Spermatogonium 64 64 Assuming the spermatogonium is in G1 prior to the production of sister chromatids in S phase, the chromosome number will be the diploid number of chromosomes.
First polar body 32 64 The first polar body is the product of meiosis I, so it will be haploid; but the sister chromatids have not separated, so each chromosome will consist of two sister chromatids. Primary oocyte 64 The primary oocyte has stopped in prophase I of meiosis. So the homologs have not yet separated, and each chromosome consists of two sister chromatids.
Secondary spermatocyte 32 64 The secondary spermatocyte is a product of meiosis I and has yet to enter meiosis II. So the secondary spermatocyte will be haploid because the homologous pairs were separated in meiosis I; but each chromosome is still composed of two sister chromatids. Indicate whether each of the following cells is haploid or diploid. Haploid or Diploid? A primary oocyte divides to give rise to a secondary oocyte and a first polar body. The secondary oocyte then divides to give rise to an ovum and a second polar body.
Is the genetic information found in the first polar body identical with that found in the secondary oocyte? Solution: No, the information is not identical with that found in the secondary oocyte.
The first polar body and the secondary oocyte are the result of meiosis I. In meiosis I, homologous chromosomes segregate and thus both the first polar body and secondary oocyte will contain only one member of each original chromosome pair, and these will have different alleles of some of the genes.
Also the recombination that took place in prophase I will have generated new and different arrangements of genetic material for each member of the pair. Is the genetic information found in the second polar body identical with that in the ovum? Solution: No, the information is not identical. The second polar body and the ovum will contain the same members of the homologous pairs of chromosomes that were separated during meiosis I and produced by the separation of sister chromatids during anaphase II.
However, the sister chromatids are no longer identical. The sister chromatids have undergone recombination during prophase I and thus contain genetic information that is not identical to the other sister chromatids. Can you think of a reason why failure of chromosome division might be more common in female gametogenesis than male gametogenesis?
Solution: Male gametogenesis, or spermatogenesis in human males, occurs regularly. Once the spermatogonium begins meiosis, the process quickly goes to completion, resulting in the formation of four spermatids that can mature into sperm cells.
Female gametogenesis, or oogenesis in human females, is more complicated. Each oogonium enters meiosis I but stops at prophase I, generating a primary oocyte. This primary oocyte remains frozen in prophase I until ovulation begins and continues through meiosis I. Only if the egg is fertilized will meiosis II be completed. Because the primary oocyte is present at birth, the completion of meiosis I by a primary oocyte may not occur for many years 35 to 40 years or more.
The length of time could lead to degradation or damaging of the meiotic machinery such as the meiotic spindle fibers or cohesin complex. The damaged meiotic machinery could result in an improper separation of homologous pairs or of sister chromatids during the meiotic process.
Add to cart. Download Sample. Student Solutions Manual for Genetic of genetics and make connections among those concepts as a way of gaining a richer understanding of the essentials of genetics.
With the new edition, Ben Pierce again focuses on the most pervasive problems for students taking genetics This Genetics: A Conceptual Approach, 6th Edition Solution Manual is designed to enhance your scores and assist in the learning process. There are many regulations of academic honesty of your institution to be considered at your own discretion while using it.
Pierce, Jung H. Choi, Mark E. Mccallum, Nov 1, , Science, pages.
0コメント