Deck 2: Mitosis and Meiosis

Question 1

A man in his early 20s received chemotherapy and radiotherapy as treatment every 60 days for Hodgkin's disease. After unsuccessful attempts to have children, he had his sperm examined at a fertility clinic, upon which multiple chromosomal irregularities were discovered. When examined within 5 days of a treatment, extra chromosomes were often present or one or more chromosomes were completely absent. However, such irregularities were not observed at day 38 or thereafter.
How might a geneticist explain the time-related differences in chromosomal irregularities?

Answer 1

Sperms are produced through a process called meiosis. Meiosis reduces the diploid number of chromosomes to haploid. Haploid refers to one set of chromosomes. The set of chromosomes may come from either the mother or the father. If meiosis takes place normally, gametes or sperms cells will receive half the number of chromosomes.
There are two anaphases in meiosis. In the first anaphase, homologous chromosomes move to opposite poles of the cell. Hence, one set of chromosomes is at one pole, and the other set is at another pole. The sister chromatids of each chromosomes are not separated during the first anaphase of meiosis.
During the process of the first meiotic telophase, the cell's cytoplasm split in half. The process is called cytokinesis. The two cells, known as secondary spermatocytes, each have half the number of chromosomes. Each chromosome of a secondary spermatocyte has two sister chromatids.
During the second anaphase of meiosis, the sister chromatids of the two spermatocytes move to opposite poles of the cells. Consequently, four gametes with half the number of chromosomes are produced at the end of meiosis. The gametes are haploids.
Irregularities in the number of chromosomes most likely occur during the two meiotic anaphases. Anaphases are where the chromosomes fail to separate normally. There are several possibilities in which sperm cells acquire abnormal number of chromosomes.
Chemotherapy and radiation could have interfered with the proper process of meiosis, particularly during the first and second meiotic anaphases.
If more than half of the chromosomes move to one pole of the cell, then less than half of the chromosomes move to the opposite pole of the cell. Some gametes or sperm cells will have extra chromosomes. The other sperm cells will have fewer than the normal number of chromosomes.
The sperm cells are normal 38 days after chemotherapy and radiation. This observation indicates that the treatment interferes with the normal process of meiosis. Meiosis undergoes normally without the treatment. Sperm cells with normal number of chromosomes are produced during the time the germ cells are not affected by the chemotherapy and radiation.

Question 2

In this chapter, we focused on how chromosomes are distributed during cell division, both in dividing somatic cells (mitosis) and in gamete-and spore-forming cells (meiosis). We found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, answer the following questions.
(a) How do we know that chromosomes exist in homologous pairs?
(b) How do we know that DNA replication occurs during interphase, not early in mitosis?
(c) How do we know that mitotic chromosomes are derived from chromatin?

Answer 2

(a)Chromosomes exist in homologous pairs. Homologous chromosomes have the same length and location of centromere. Centromere is region of constriction. The centromere holds the sister chromatids together. The location of centromere on a chromosome is described as metacentric, submetacentric, acrocentric, and telocentric.
The karyotype shows all 46 chromosomes of human somatic cells. According to the karyotype, there are twenty two pairs of chromosomes with the same lengths and same locations of centromeres.
The sex chromosomes are not homologous with the Y chromosomes. The Y chromosome is shorter than the X chromosome.
The X chromosome and the Y chromosome determine an organism's gender, but they are not homologous. The X chromosome and the Y chromosome do not have the same length and same location of centromere.
(b)Chromosome replication occurs during interphase and not during mitosis. During interphase, chromosomes uncoiled. The DNA strands are thin and not visible. Chromosomes are observable during the prophase of mitosis. During prophase, chromosomes coil up and condense. The chromosomes during prophase are visible under electron microscopy.
(c)Chromatins are complex of DNA, RNA, histones, and non-histones proteins. Chromatins are uncoiled chromosomes during the interphase. Photograph of electron microscopy reveals the structures of chromatin and chromosome during stages of the cell cycle.

Question 3

A man in his early 20s received chemotherapy and radiotherapy as treatment every 60 days for Hodgkin's disease. After unsuccessful attempts to have children, he had his sperm examined at a fertility clinic, upon which multiple chromosomal irregularities were discovered. When examined within 5 days of a treatment, extra chromosomes were often present or one or more chromosomes were completely absent. However, such irregularities were not observed at day 38 or thereafter.
Do you think that exposure to chemotherapy and radiotherapy of a spermatogonium would cause more problems than exposure to a secondary spermatocyte?

Answer 3

Spermatogonium is a diploid germ cell. All gametes are produced from germ cells. A secondary spermatocyte is produced from the first anaphase of oogenesis.
Damages to the secondary spermatocytes would not affect the spermatogonium. However, damage to the spermatogonium will affect the production of the secondary spermatocyte.
Exposure to chemotherapy and radiotherapy would cause problems to both the spermatogonium and the secondary spermatocyte. Both the spermatogonium and the secondary spermatocyte would be damaged.
However, damage to the spermatogonium would cause more problems than damage to the secondary spermatocyte. If the spermatogonium is damaged, there is no germ cell for meiosis to produce gametes. Individual with damaged spermatogonium would not be able to produce sperms. Hence, that person would be sterile and would not be able to have children.
Therefore, damage to the spermatogonium could cause more problems than damage to the secondary spermatocyte.

Question 4

Review the Chapter Concepts list. All of these pertain to conceptual issues involving mitosis or meiosis. Based on these concepts, write a short essay that contrasts mitosis and meiosis, including their respective roles in organisms, the mechanisms by which they achieve their respective outcomes, and the consequences should either process fail to be executed with absolute fidelity.
CHAPTER CONCEPTS
▪Genetic continuity between generations of cells and between generations of sexually reproducing organisms is maintained through the processes of mitosis and meiosis, respectively.
▪Diploid eukaryotic cells contain their genetic information in pairs of homologous chromosomes, with one member of each pair being derived from the maternal parent and one from the paternal parent.
▪Mitosis provides a mechanism by which chromosomes, having been duplicated, are distributed into progeny cells during cell reproduction.
▪Mitosis converts a diploid cell into two diploid daughter cells.
▪The process of meiosis distributes one member of each homologous pair of chromosomes into each gamete or spore, thus reducing the diploid chromosome number to the haploid chromosome number.
▪Meiosis generates genetic variability by distributing various combinations of maternal and paternal members of each homologous pair of chromosomes into gametes or spores.
▪During the stages of mitosis and meiosis, the genetic material is condensed into discrete structures called chromosomes.

Question 5

A man in his early 20s received chemotherapy and radiotherapy as treatment every 60 days for Hodgkin's disease. After unsuccessful attempts to have children, he had his sperm examined at a fertility clinic, upon which multiple chromosomal irregularities were discovered. When examined within 5 days of a treatment, extra chromosomes were often present or one or more chromosomes were completely absent. However, such irregularities were not observed at day 38 or thereafter.
What is the obvious advice that the man received regarding fertility while he remained under treatment?

Question 6

What role do the following cellular components play in the storage, expression, or transmission of genetic information: (a) chromatin, (b) nucleolus, (c) ribosome, (d) mitochondrion, (e) centriole, (f) centromere?

Question 7

Discuss the concepts of homologous chromosomes, diploidy, and haploidy. What characteristics do two homologous chromosomes share?

Question 8

If two chromosomes of a species are the same length and have similar centromere placements and yet are not homologous, what is different about them?

Question 9

Describe the events that characterize each stage of mitosis.

Question 10

How are chromosomes named on the basis of their centromere placement?

Question 11

Contrast telophase in plant and animal mitosis.

Question 12

Describe the phases of the cell cycle and the events that characterize each phase.

Question 13

Define and discuss these terms: (a) synapsis, (b) bivalents, (c) chiasmata, (d) crossing over, (e) chromomeres, (f) sister chromatids, (g) tetrads, (h) dyads, (i) monads.

Question 14

Contrast the genetic content and the origin of sister versus nonsister chromatids during their earliest appearance in prophase I of meiosis. How might the genetic content of these change by the time tetrads have aligned at the equatorial plate during metaphase I?

Question 15

Given the end results of the two types of division, why is it necessary for homologs to pair during meiosis and not desirable for them to pair during mitosis?

Question 16

Contrast spermatogenesis and oogenesis. What is the significance of the formation of polar bodies?

Question 17

Explain why meiosis leads to significant genetic variation while mitosis does not.

Question 18

A diploid cell contains three pairs of homologous chromosomes designated C1 and C2, M1 and M2, and S1 and S2. No crossing over occurs. What combinations of chromosomes are possible in (a) daughter cells following mitosis? (b) cells undergoing the first meiotic metaphase? (c) haploid cells following both divisions of meiosis?

Question 19

Considering the preceding problem, predict the number of different haploid cells that could be produced by meiosis if a fourth chromosome pair (W1 and W2) were added.

Question 20

During oogenesis in an animal species with a haploid number of 6, one dyad undergoes nondisjunction during meiosis II. Following the second meiotic division, this dyad ends up intact in the ovum. How many chromosomes are present in (a) the mature ovum and (b) the second polar body? (c) Following fertilization by a normal sperm, what chromosome condition is created?

Question 21

What is the probability that, in an organism with a haploid number of10, a sperm will be formed that contains all 10 chromosomes whose centromeres were derived from maternal homologs?

Question 22

During the first meiotic prophase, (a) when does crossing over occur; (b) when does synapsis occur; (c) during which stage are the chromosomes least condensed; and (d) when are chias-mata first visible?

Question 23

Describe the role of meiosis in the life cycle of a vascular plant.

Question 24

Contrast the chromatin fiber with the mitotic chromosome. How are the two structures related?

Question 25

Describe the "folded-fiber" model of the mitotic chromosome.

Question 26

You are given a metaphase chromosome preparation (a slide) from an unknown organism that contains 12 chromosomes. Two that are clearly smaller than the rest appear identical in length and centromere placement. Describe all that you can about these chromosomes.

Question 27

If one follows 50 primary oocytes in an animal through their various stages of oogenesis, how many secondary oocytes would be formed? How many first polar bodies would be formed? How many ootids would be formed? If one follows 50 primary spermatocytes in an animal through their various stages of spermatogenesis, how many secondary spermatocytes would be formed? How many spermatids would be formed?

Question 28

The nuclear DNA content of a single sperm cell in Drosophila melanogaster is approximately 0.18 picogram. What would be the expected nuclear DNA content of a primary spermatocyte in Drosophila ? What would be the expected nuclear DNA content of a somatic cell (non-sex cell) in the G1 phase? What would be the expected nuclear DNA content of a somatic cell at metaphase?

Question 29

As part of the " Problems and Discussion Questions " section in this and each subsequent chapter, we shall present a number of " ExtraSpicy " genetics problems. We have chosen to set these apart in order to identify problems that are particularly challenging. You may be asked to examine and assess actual data, to design genetics experiments, or to engage in cooperative learning. Like genetic varieties of peppers, some of these experiences are just spicy and some are very hot. We hope that you will enjoy the challenges that they pose.
Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., A m and A p ). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis. You may wish to use a large piece of brown manila wrapping paper or a cut-up paper grocery bag for this project and to work in partnership with another student. We recommend cooperative learning as an efficacious way to develop the skills you will need for solving the problems presented throughout this text.
In mitosis, what chromatid combination(s) will be present during metaphase? What combination(s) will be present at each pole at the completion of anaphase?

Question 30

As part of the " Problems and Discussion Questions " section in this and each subsequent chapter, we shall present a number of " ExtraSpicy " genetics problems. We have chosen to set these apart in order to identify problems that are particularly challenging. You may be asked to examine and assess actual data, to design genetics experiments, or to engage in cooperative learning. Like genetic varieties of peppers, some of these experiences are just spicy and some are very hot. We hope that you will enjoy the challenges that they pose.
Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., A m and A p ). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis. You may wish to use a large piece of brown manila wrapping paper or a cut-up paper grocery bag for this project and to work in partnership with another student. We recommend cooperative learning as an efficacious way to develop the skills you will need for solving the problems presented throughout this text.
During meiosis I, assuming no crossing over, what chromatid combination(s) will be present at the completion of prophase? Draw all possible alignments of chromatids as migration begins during early anaphase.

Question 31

As part of the " Problems and Discussion Questions " section in this and each subsequent chapter, we shall present a number of " ExtraSpicy " genetics problems. We have chosen to set these apart in order to identify problems that are particularly challenging. You may be asked to examine and assess actual data, to design genetics experiments, or to engage in cooperative learning. Like genetic varieties of peppers, some of these experiences are just spicy and some are very hot. We hope that you will enjoy the challenges that they pose.
Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., A m and A p ). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis. You may wish to use a large piece of brown manila wrapping paper or a cut-up paper grocery bag for this project and to work in partnership with another student. We recommend cooperative learning as an efficacious way to develop the skills you will need for solving the problems presented throughout this text.
Are there any possible combinations present during prophase of meiosis II other than those that you drew in Problem 27? If so, draw them.

Question 32

As part of the " Problems and Discussion Questions " section in this and each subsequent chapter, we shall present a number of " ExtraSpicy " genetics problems. We have chosen to set these apart in order to identify problems that are particularly challenging. You may be asked to examine and assess actual data, to design genetics experiments, or to engage in cooperative learning. Like genetic varieties of peppers, some of these experiences are just spicy and some are very hot. We hope that you will enjoy the challenges that they pose.
Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., A m and A p ). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis. You may wish to use a large piece of brown manila wrapping paper or a cut-up paper grocery bag for this project and to work in partnership with another student. We recommend cooperative learning as an efficacious way to develop the skills you will need for solving the problems presented throughout this text.
Draw all possible combinations of chromatids during the early phases of anaphase in meiosis II.

Question 33

As part of the " Problems and Discussion Questions " section in this and each subsequent chapter, we shall present a number of " ExtraSpicy " genetics problems. We have chosen to set these apart in order to identify problems that are particularly challenging. You may be asked to examine and assess actual data, to design genetics experiments, or to engage in cooperative learning. Like genetic varieties of peppers, some of these experiences are just spicy and some are very hot. We hope that you will enjoy the challenges that they pose.
Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., A m and A p ). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis. You may wish to use a large piece of brown manila wrapping paper or a cut-up paper grocery bag for this project and to work in partnership with another student. We recommend cooperative learning as an efficacious way to develop the skills you will need for solving the problems presented throughout this text.
Assume that during meiosis I none of the C chromosomes disjoin at metaphase, but they separate into dyads (instead of monads) during meiosis II. How would this change the alignments that you constructed during the anaphase stages in mei-osis I and II? Draw them.

Question 34

As part of the " Problems and Discussion Questions " section in this and each subsequent chapter, we shall present a number of " ExtraSpicy " genetics problems. We have chosen to set these apart in order to identify problems that are particularly challenging. You may be asked to examine and assess actual data, to design genetics experiments, or to engage in cooperative learning. Like genetic varieties of peppers, some of these experiences are just spicy and some are very hot. We hope that you will enjoy the challenges that they pose.
Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., A m and A p ). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis. You may wish to use a large piece of brown manila wrapping paper or a cut-up paper grocery bag for this project and to work in partnership with another student. We recommend cooperative learning as an efficacious way to develop the skills you will need for solving the problems presented throughout this text.
Assume that each gamete resulting from Problem 30 fuses, in fertilization, with a normal haploid gamete. What combinations will result? What percentage of zygotes will be diploid, containing one paternal and one maternal member of each chromosome pair?

Question 35

As part of the " Problems and Discussion Questions " section in this and each subsequent chapter, we shall present a number of " ExtraSpicy " genetics problems. We have chosen to set these apart in order to identify problems that are particularly challenging. You may be asked to examine and assess actual data, to design genetics experiments, or to engage in cooperative learning. Like genetic varieties of peppers, some of these experiences are just spicy and some are very hot. We hope that you will enjoy the challenges that they pose.
▪species of cereal rye ( Secale cereale ) has a chromosome number of 14, while a species of Canadian wild rye ( Elymus canadensis ) has a chromosome number of 28. Sterile hybrids can be produced by crossing Secale with Elymus.
(a) What would be the expected chromosome number in the somatic cells of the hybrids?
(b) Given that none of the chromosomes pair at meiosis I in the sterile hybrid (Hang and Franckowlak, 1984), speculate on the anaphase I separation patterns of these chromosomes.

Question 36

As part of the " Problems and Discussion Questions " section in this and each subsequent chapter, we shall present a number of " ExtraSpicy " genetics problems. We have chosen to set these apart in order to identify problems that are particularly challenging. You may be asked to examine and assess actual data, to design genetics experiments, or to engage in cooperative learning. Like genetic varieties of peppers, some of these experiences are just spicy and some are very hot. We hope that you will enjoy the challenges that they pose.
An interesting procedure has been applied for assessing the chromosomal balance of potential secondary oocytes for use in human in vitro fertilization. Using fluorescence in situ hybridization (FISH), Kuliev and Verlinsky (2004) were able to identify individual chromosomes in first polar bodies and thereby infer the chromosomal makeup of "sister" oocytes. Assume that when examining a first polar body you saw that it had one copy (dyad) of each chromosome but two dyads of chromosome 21. What would you expect to be the chromosomal 21 complement in the secondary oocyte? What consequences are likely in the resulting zygote, if the secondary oocyte was fertilized?

Question 37

As part of the " Problems and Discussion Questions " section in this and each subsequent chapter, we shall present a number of " ExtraSpicy " genetics problems. We have chosen to set these apart in order to identify problems that are particularly challenging. You may be asked to examine and assess actual data, to design genetics experiments, or to engage in cooperative learning. Like genetic varieties of peppers, some of these experiences are just spicy and some are very hot. We hope that you will enjoy the challenges that they pose.
Assume that you were examining a first polar body and noted that it had one copy (dyad) of each chromosome except chromosome 21. Chromosome 21 was completely absent. What would you expect to be the chromosome 21 complement (only with respect to chromosome 21) in the secondary oocyte? What consequences are likely in the resulting zygote if the secondary oocyte was fertilized?

Question 38

As part of the " Problems and Discussion Questions " section in this and each subsequent chapter, we shall present a number of " ExtraSpicy " genetics problems. We have chosen to set these apart in order to identify problems that are particularly challenging. You may be asked to examine and assess actual data, to design genetics experiments, or to engage in cooperative learning. Like genetic varieties of peppers, some of these experiences are just spicy and some are very hot. We hope that you will enjoy the challenges that they pose.
Kuliev and Verlinsky (2004) state that there was a relatively high number of separation errors at meiosis I. In these cases the centromere underwent a premature division, occurring at meiosis I rather than meiosis II. Regarding chromosome 21, what would you expect to be the chromosome 21 complement in the secondary oocyte in which you saw a single chromatid (monad) for chromosome 21 in the first polar body? If this secondary oocyte was involved in fertilization, what would be the expected consequences?