Biological Sciences
Comparison of Mitosis and Meiosis
Mitosis and meiosis are both processes of cell division, but they have distinct differences. Mitosis results in two identical daughter cells, while meiosis produces four genetically diverse daughter cells. Mitosis is involved in growth, repair, and asexual reproduction, while meiosis is specific to sexual reproduction and leads to genetic variation.
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12 Key excerpts on "Comparison of Mitosis and Meiosis"
eBook - PDF- Emea, A(Authors)
- 2018(Publication Date)
- Agri Horti Press(Publisher)
There are, however, essential differences between the five proceses, some of which are the following : 1. Mitosis occurs in all somatic cells of an individual, but meiosis is limited to only the germinal cells. This ebook is exclusively for this university only. Cannot be resold/distributed. Cell Biology, Physiology and Mycology 28 2. In mitosis each replication cycle of DNA is followed by one cell division. The resulting daughter cells have diploid number of chromosomes and the same amount of DNA as the parent cell. In meiosis one replication cycle of DNA is followed by two divisions, and the four cells are haploid and contain half the amount of DNA. 3. In mitosis DAN synthesis occurs in the S period, which is followed by a G 2 phase before the onset of division. In meiosis there is premeiotic DNA synthesis which is much longer than that in mitosis and which is followed immediately by meiosis. In other words, the G 2 phase is short of non-existent. 4. In mitosis every chromosome behaves independently; in meiosis the homologous chromosomes become mechanically related during the first mechanically related during the first meiotic division. ( i.e. , meiotic pairing). While mitosis is rather brief (one or two hours), meiosis is a long process. For example, in the human male it may last 24 days, and in the female it may go on for several years. 5. A fundamental difference between the two types of cell division is that in mitosis the genetic material remains constant ( i.e. , with only rare mutations or chromosomal aberrations,) while genetic variability is one of main consequences of meiosis. Several mitotic divisions of the spermatogonia (or oögonia), meiotic division starts A kind of switch shifts these cells from mitosis to meiosis.
eBook - PDF- Julianne Zedalis, John Eggebrecht(Authors)
- 2018(Publication Date)
- Openstax(Publisher)
However, unlike mitosis, in which there is just one nuclear division, meiosis has two complete rounds of nuclear division—meiosis I and meiosis II. These result in four nuclei and (usually) four daughter cells, each with half the number of chromosomes as the parent cell (1n). The first division, meiosis I, separates homologous chromosomes, and the second division, meiosis II, separates chromatids. (Remember: during meiosis, DNA replicates ONCE but divides TWICE, whereas in mitosis, DNA replicates ONCE but divides only ONCE.). Although mitosis and meiosis are similar in many ways, they have different outcomes. The main difference is in the type of cell produced: mitosis produces identical cells, allowing growth or repair of tissues; meiosis generates reproductive cells, or gametes. Gametes, often called sex cells, unite with other sex cells to produce new, unique organisms. Genetic variation occurs during meiosis I, in which homologous chromosomes pair and exchange non-sister chromatid segments (crossover). Here the homologous chromosomes separate into different nuclei, causing a reduction in “ploidy.” During meiosis II—which is more similar to a mitotic division—the chromatids separate and segregate into four haploid sex cells. However, because of crossover, the resultant daughter cells do not contain identical genomes. As in mitosis, external factors and internal signals regulate the meiotic cell cycle. As we will explore in more detail in a later chapter, errors in meiosis can cause genetic disorders, such as Down syndrome. Information presented and the examples highlighted in the section support concepts and learning objectives outlined in Big Idea 3 of the AP ® Biology Curriculum Framework. The learning objectives listed in the Curriculum Framework provide a transparent foundation for the AP ® Biology course, an inquiry-based laboratory experience, instructional activities, and AP ® exam questions.
eBook - PDF- Ram J. Singh(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
85 4 Cell Division 4.1 INTRODUCTION Cell division is a continuous process that occurs in all living organisms. It has been divided into two categories: mitosis and meiosis. Both forms of nuclear division occur in eukaryotes and these pro-cesses comprise the cell cycle: G 1 (growth) → S (synthesis of DNA) → G 2 (growth) → M (mitosis or meiosis) → C (cytokinesis) (Smith and Kindfield, 1999). Mitosis occurs in somatic tissues where each chromosome is divided identically into halves, both qualitatively and quantitatively, producing genetically identical to the parent nucleus. In contrast, meiosis takes place in germ cells with the consequence that nuclei with haploid chromosome numbers are produced. Both types of cell divi-sion play an important role in the development and hereditary continuity of a eukaryotic organism. 4.2 MITOSIS 4.2.1 P ROCESS OF M ITOSIS The term mitosis is derived from the Greek word mitos for thread; coined by Flemming in 1879 (see Chapter 1 ). The synonym of mitosis is karyokinesis, that is, the actual division of a nucleus into two identical parental daughter nuclei. It is also known as equational division because the exact longitudinal division of each chromosome into identical chromatids and their precise distribution into daughter nuclei leads to the formation of two cells; identical to the original cell from which they were derived. The process of mitotic cell division has been divided into six stages: (1) interphase, (2) prophase, (3) metaphase, (4) anaphase, (5) telophase, and (6) cytokinesis. 4.2.1.1 Interphase Two more terms, resting stage and metabolic stage, have been used to identify interphase cells. However, interphase cells should not be described as being in a “resting stage” because their nuclei are very active as they prepare for cell division. The DNA replication and transcription occur during interphase (Manuelidis, 1990).
eBook - ePub- Ram J. Singh(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
4 Cell Division 4.1 INTRODUCTIONCell division is a continuous process that occurs in all living organisms. It has been divided into two categories: mitosis and meiosis. Both forms of nuclear division occur in eukaryotes and these processes comprise the cell cycle: G1 (growth) → S (synthesis of DNA) → G2 (growth) → M (mitosis or meiosis) → C (cytokinesis) (Smith and Kindfield, 1999). Mitosis occurs in somatic tissues where each chromosome is divided identically into halves, both qualitatively and quantitatively, producing genetically identical to the parent nucleus. In contrast, meiosis takes place in germ cells with the consequence that nuclei with haploid chromosome numbers are produced. Both types of cell division play an important role in the development and hereditary continuity of a eukaryotic organism.4.2 MITOSIS4.2.1 PROCESS OF MITOSISThe term mitosis is derived from the Greek word mitos for thread; coined by Flemming in 1879 (see Chapter 1 ). The synonym of mitosis is karyokinesis, that is, the actual division of a nucleus into two identical parental daughter nuclei. It is also known as equational division because the exact longitudinal division of each chromosome into identical chromatids and their precise distribution into daughter nuclei leads to the formation of two cells; identical to the original cell from which they were derived.The process of mitotic cell division has been divided into six stages: (1) interphase, (2) prophase, (3) metaphase, (4) anaphase, (5) telophase, and (6) cytokinesis. 4.2.1.1 InterphaseTwo more terms, resting stage and metabolic stage, have been used to identify interphase cells. However, interphase cells should not be described as being in a “resting stage” because their nuclei are very active as they prepare for cell division. The DNA replication and transcription occur during interphase (Manuelidis, 1990). Interphase consists of three phases: G1 (gap 1; pre-DNA synthesis) phase, S phase (DNA synthesis), and G2 (gap 2; post-DNA synthesis). The duration of mitotic division is short compared to time required for the cells going through interphase (Figure 4.1 ). Thus, “metabolic stage” is a more appropriate term for the interphase cells. The interphase nucleus contains one or more prominent nucleoli and numerous chromocenters depending on the heterochromatic nature of the chromosomes. Chromosomes cannot be traced individually and they are very lightly stained (Figure 4.2a
eBook - PDF- Cecie Starr, Beverly McMillan(Authors)
- 2015(Publication Date)
- Cengage Learning EMEA(Publisher)
Two rounds of division, called meiosis I and meiosis II, produce gametes that are haploid cells, with half the diploid number of chromosomes. Table 18.1 summarizes the differences between mitosis and meiosis, which we’ll look at in more detail in the following sections. Figure 18.5 Meiosis halves the chromosome number. A In meiosis I, each duplicated chromosome in the nucleus pairs with its homologous partner. C Sister chromatids separate in meiosis II. The now undupli-cated chromosomes are packaged into four new nuclei. B Homologous partners separate. The still-duplicated chromosomes are packaged into two new nuclei. Mitosis Meiosis Function Growth, including Gamete production repairing and maintaining (sperm/eggs) tissues Occurs in Somatic (body) cells Germ cells in gonads (testes and ovaries) Mechanism Chromosomes are Chromosomes are duplicated once, then duplicated twice, the cytoplasm is divided then the cytoplasm is divided Outcome Maintains the diploid Halves the diploid chromosome number chromosome (2 n → 2 n ) number (2 n → n ) Effect Two diploid Four haploid daughter cells daughter cells TABLE 18.1 Overview of Mitosis and Meiosis one chromatid centromere its sister chromatid a chromosome (unduplicated) a chromosome (duplicated) © Cengage Learning © Cengage Learning centromere Constricted area where sister chroma-tids attach to each other. meiosis Process that divides the nucleus in a dividing germ cell in a way that halves the chromosome number in daughter cells. sister chromatids A dupli-cated chromosome and its copy. Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience.
- Cecie Starr, Christine Evers, Lisa Starr, , Cecie Starr, Cecie Starr, Christine Evers, Lisa Starr(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
● ● Offspring of sexual reproducers inherit new combinations of parental alleles, so they differ from one another and from their parents. 9.6 Meiosis in Sexual Reproduction LEARNING OBJECTIVES ●●● ● Describe the relationship between germ cells and gametes. ●●● ● Explain why sexual reproduction requires meiosis. ●●● ● Describe crossing over and how it fosters diversity among the offspring of sexual reproducers. Most body cells are diploid (2n), with two copies of each chromosome—one inherited from each of two parents. A reproductive cell such as an egg or sperm is haploid (n), which means it has one copy of each chromosome. Meiosis is a nuclear division mechanism that halves the chromosome number, and it is essential to the formation of haploid cells. Stages of Meiosis The process of meiosis is similar to mitosis in several ways. A cell replicates its DNA before either nuclear division process begins, so each chromosome consists of two sister chromatids. As in mitosis, a spindle forms, and its microtubules move the chromosomes. However, meiosis sorts the chromosomes into new nuclei not once but twice. The two consecutive nuclear divisions are called meiosis I and meiosis II. Figure 9.16 (next page) shows the stages of meiosis in a diploid (2n) cell. Meiosis I The first stage of meiosis I is prophase I. During this stage, the chromo- somes pack tightly, and homologous chromosomes align tightly and swap segments haploid Having one of each type of chromosome. meiosis Nuclear division process that halves the chromosome number. Basis of sexual reproduction. sexual reproduction Reproductive mode by which offspring arise from two parents and inherit genes from both. Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
eBook - ePub- Julia E. Richards, R. Scott Hawley(Authors)
- 2010(Publication Date)
- Academic Press(Publisher)
In humans the result of meiosis I is two daughter cells each of which has 23 chromosomes. It is critical to note that what segregates at meiosis I is whole chromosomes – not sister chromatids! When chromosome 1 separates from its partner it does not separate its two sister chromatids! It is precisely this absence of sister chromatid separation that necessitates the mitosis-like second meiotic division, known as meiosis II. In a human cell that has just finished meiosis, the individual chromosomes now line up on a newly built spindle, with their sister chromatids pointed toward opposite poles, just as they do during a mitotic division. This is known as metaphase II. When you think of it, meiosis II is really just like any other mitosis, just with half the number of chromosomes.The process of meiosis in humans is diagrammed schematically in Figure 6.13 , which shows a cell with a pair of homologous chromosomes. This figure shows both the separation of the chromosomes during the two meiotic divisions (seen for spermatogenesis on the left). It also shows a fundamental difference between meiosis in males and females. In males all four products of meiosis become sperm. But in females the cell divisions are grossly unequal, resulting in one very large cell that keeps virtually all the cytoplasm and three tiny cells, called polar bodies, that are discarded and then die.As we continue our discussion it is important to focus on two questions. First, what is a meiotic cell trying to do in terms of the chromosomes? The answer is that meiosis functions to precisely reduce the chromosome number by one-half. The second question is: what is the cell trying to do in terms of building two very different types of cells, a sperm and an egg? Sperm cells are short-lived and consist basically of a propulsion system that allows them to swim and a DNA “payload”. An egg, on the other hand, needs to have all of the resources and information required for a zygote to become a rather complex embryo capable of attaching itself to the endometrium of the mother’s uterus. A single conception event usually involves hundreds of millions of sperm donated by the father (only one of which succeeds in fertilization!) and a single egg provided by the mother. These are very different cells and not surprisingly they have very different histories.Meiosis Is Executed Quite Differently in Human Males and Females Given the importance of this process, it is surprising that it takes place in such different fashions and at different times in men and women, but it does, and these differences are truly impressive.The most notable sex difference is in the timing of meiosis. In human females, meiosis begins during fetal development. Most if not all of the oocytes (eggs) that a human female will possess in her lifetime are produced while she is still in utero
eBook - PDF- Donald Voet, Judith G. Voet(Authors)
- 2023(Publication Date)
- Wiley(Publisher)
b. Germ Cells Are Formed by Meiosis The formation of germ cells, a process known as meiosis (Fig. 1-22), requires two consecutive cell divisions. Before the first meiotic division each chromosome replicates, but the resulting sister chromatids remain attached at their cen- tromere. The homologous pairs of the doubled chromosomes then line up across the equatorial plane of the cell in zipper- like fashion, which permits an exchange of the corresponding sections of homologous chromosomes in a process known as crossing-over. The spindle then moves the members of Figure 1-20 Chromosomes. A photomicrograph of a plant cell (Scadoxus katherinae Bak.) during anaphase of mitosis showing its chromosomes being pulled to opposite poles of the cell by the mitotic spindle. The microtubules forming the mitotic spindle are stained red and the chromosomes are blue. [Courtesy of Andrew S. Bajer, University of Oregon.] Figure 1-21 Mitosis, the usual form of cell division in eukaryotes. Mitosis yields two daughter cells, each with the same chromosomal complement as the parental cell. Section 1-4 Genetics: An Overview 25 each homologous pair to opposite poles of the cell so that, after the first meiotic division, each daughter cell contains N doubled chromosomes. In the second meiotic division, the sister chromatids separate to form chromosomes and move to opposite poles of the dividing cell to yield a total of four haploid cells that are known as gametes. Fertilization consists of the fusion of a male gamete (sperm) with a female gam- ete (ovum) to yield a diploid cell known as a zygote that has received N chromosomes from each of its parents. B. Mendelian Inheritance The basic laws of inheritance were reported in 1866 by Gregor Mendel.
eBook - PDFMolecular Cytology V1
The Cell Cycle
- Jean Brachet(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
Reductional division is due to the fact that, during meiosis, the kinetochores do not divide at metaphase-anaphase. The molecular reasons for this remain unknown. There is another major difference between meiosis and mitosis. Genetic re-combination, through crossing-over, occurs between homologous chromosomes at the pachytene stage (Fig. 47). An equivalent to crossing-over, in somatic cells, is chromatid (sister or nonsister) exchange (SCE). As we have seen, SCE is an extremely rare event during normal cell division. It is a sensitive symptom of DNA damage, and we have therefore described it as one of the chromosomal abnormalities that can occur during mitosis in injured cells. Even in somatic hybrids, in which recombination events might have been expected to take place at a higher rate than in normal cells, mitotic recombination remains a very rare event (Tarrant and Holliday, 1977). Since DNA damage is followed by DNA repair, one would expect DNA repair mechanisms to be at work during the pachytene stage of meiosis. This has been conclusively shown by the work of Stern and Hotta (reviewed in 1980) on DNA metabolism during meiosis. 366 5. CELL DIVISION Finally, another characteristic of meiosis is the fact that the homologous chromosomes are held together by the so-called synaptinemal complexes (Fig. 48) that have been recently isolated, at the pachytene stage of meiosis, from hamster testis by Walmsley and Moses (1981). Their structure can be studied under the light microscope after silver staining (Dresser and Moses, 1980; Fig. 49) or under the electron microscope. Their main components are two lateral elements (40-60 nm thick) and one central element (20-40 nm thick). The central element is a DNA fiber, while the lateral elements are composed of proteins and RNA (Solari, 1972; Esponda and Gimenez-Martin, 1973).
eBook - PDF- D. Peter Snustad, Michael J. Simmons(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
The double fertilization that occurs during Arabidopsis reproduction creates a diploid zygote, which develops into an embryo, and a triploid endosperm, which develops into nutritive tissue in the seed. In mice and other mammals, one cell from female meiosis becomes the egg, whereas all four cells from male meiosis become sperm. Testing Your Knowledge 37 Testing Your Knowledge Integrate Different Concepts and Techniques 1. What are the principal differences between mitosis and meiosis? Answer: In mitosis, one division event follows one round of chro- mosome duplication. In meiosis, two division events follow one round of chromosome duplication. Furthermore, dur- ing the first meiotic division, homologous chromosomes pair with each other. This homology-based pairing does not normally occur during mitosis. The two cells produced by a mitotic division are identical to each other and to the mother cell from which they were derived. The four cells produced by the two successive meiotic divisions are not identical to each other or to the mother cell from which they were derived. When a diploid cell undergoes mitosis, the two cells derived from it will also be diploid. When a diploid cell undergoes meiosis, the four cells derived from it will be haploid. 2. Caenorhabditis elegans, a small nonparasitic worm, is used in genetics research. Some of these worms are hermaphrodites capable of producing both eggs and sperm. C. elegans her- maphrodites have five pairs of chromosomes. How many chromosomes are present (a) in a sperm cell from a her- maphrodite? (b) in a fertilized egg from a hermaphrodite? How many sister chromatids are present in a hermaphro- dite’s cell that (c) is entering the first meiotic division? (d) is entering the second meiotic division? (e) has com- pleted the second meiotic division? Answer: (a) Five, because a sperm cell is haploid. (b) 10, because a fertilized egg contains chromosomes from the egg and the sperm that fertilized it.
eBook - PDFCells and Tissues in Culture
Methods, Biology and Physiology
- E. N. Willmer(Author)
- 2015(Publication Date)
- Academic Press(Publisher)
These 204 H. FIRKET reviews are often longer than the present chapter could reasonably be, so the latter is bound to be very incomplete. Most of the older literature was reviewed in Hughes' book The Mitotic Cycle (1952) and the very large and recent treatise by Mazia (1961) covers an immense and varied ground. In this chapter we cannot completely exclude discussion of various cells whose behaviour may be rather different from that of animal tissue cells; it would be rather arbitrary to do so. But, in centering on cultured somatic vertebrate cells, the homogeneity of the material is increased and the problems may perhaps be better cir-cumscribed. As in all other fields of Cell Biology, the trends have been towards a more physiological approach and an evaluation of chemical events. The electron-microscope has made less impact on this than it has in other chapters of Cytology. For the first time, the question of the mechanism of mitosis has begun to emerge from the domain of speculation. The most important point acquired about cell division in the last decade is that it does not consist of a rapid duplication of cell elements, but essentially of an equal separation of parts previously synthesized. Indeed, mitosis could be said to be mainly movement and catabolism, the necessary anabolic part of cell multiplication having occurred earlier. This is found to be true of all parts and constituents of the cell, as technical advances pro-gressively permit their separate study. This justifies the amount of space devoted in this chapter to events occurring before mitosis. II. MITOSIS A. GENERAL SURVEY 1. Definition of Phases It is not necessary here to give again at length the classical description of mitosis, familiar to every reader. Observation of living cells by phase-contrast has brought about a habit of subdividing mitosis into 5 phases, separated by sudden morphological changes—not always so easy to identify on fixed cells—rather than the old-time 4 stages.
eBook - PDF- Peter Moens(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
In a microscope preparation of live spermatocytes, metaphase I stage suddenly ends as the separating chromosomes move simultaneously and rapidly (1 1. Introduction to Meiosis 5 /min) to the poles of the cell. This first meiotic anaphase (Fig. lg, h) is the cardinal moment in the meiocyte when the mixture of two genomes is sorted out into two single genomes. Each genome contains a complete set of chromosomes but the two sets are different in genetic detail. If, for example, the metaphase I bivalents of Fig. If divide into the anaphase I of Fig. Ih, then the distribution of thick and thin lines represents the mix of original maternal and paternal contribu- tions in the two separating genomes. No two spermatocytes will have the same mix. The thoroughness of the mix is generated from two sources, the random orientation of bivalents at the metaphase plate in regard to parental origin and the exchange between non-sister chromatids. Since the chromosomes were duplicated before they paired at meiotic pro- phase, the anaphase I chromosomes can enter the second metaphase of meiosis immediately, without an intervening duplicating stage (Fig. li). Metaphase II is followed by a second meiotic anaphase which reduces the single genomes of duplicated chromosomes to single genomes of single DNA content (Fig. lj). The remarkable similarity of the meiotic process, even between biological kingdoms, is evident from a comparison of meiosis in a grasshopper (Fig. 1) with meiosis in the Easter lily, Lilium longiflorum (Fig. 2). In the lily two sets of 12 chromosomes pair during meiotic prophase producing the pachytene stage of meiosis with an intractable tangle of long bivalents (Fig. 2a). Much of the biochemistry of meiosis discussed in Chapter 10 was done with these chromo- somes. When the 12 bivalents shorten during prophase, they become indi- vidually recognizable (Fig. 2b). The diplotene bivalents obviously resemble, in chromatid and chiasma structure, those of the grasshopper in Fig.
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