Tuesday, January 24, 2023

What Is Meiosis In Biology

Don't Miss

Differences Between Meiosis I And Mitosis

Meiosis | Genetics | Biology | FuseSchool

Now that we have discussed the details of meiosis I, you may realize some similarities between this stage of meiosis and mitosis. For the most part, the machinery and steps we discussed in meiosis are the same for mitosis, i.e. centrosomes, spindle fibers , and lining up at the metaphase plate. However, important differences between meiosis I and mitosis are highlighted in Table 1.

Study tip: Check out our article on Mitosis to review!

Table 1: Differences between mitosis and meiosis I.

What Is Meiosis In Biology

Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells. This process is required to produce egg and sperm cells for sexual reproduction. Meiosis begins with a parent cell that is diploid, meaning it has two copies of each chromosome.

What is Nondisjunction?

Definition of nondisjunction : failure of homologous chromosomes or sister chromatids to separate subsequent to metaphase in meiosis or mitosis so that one daughter cell has both and the other neither of the chromosomes.

What are the similarities and differences between mitosis and meiosis?

Mitosis and meiosis have different purposes, but share common features in how they work. Knowing their similarities is the beginning of understanding how they are different. The fundamental difference between mitosis and meiosis is that mitosis produces two daughter cells with the same number of chromosomes as the parent cell.

Biological Importance Of Meiosis

What is the function of meiosis in reproduction? For every organ that reproduces sexually, meiosis and mitosis are two essential parts of their cell cycle because of the balance between the number of chromosomes that are doubled during fertilization and the halving of chromosomes during gamete formation by meiosis is maintained. A sexually reproducing organism has a cell cycle that consists of two main phases: a haploid phase and a diploid phase. Meiosis definition biology is the haploid phase that starts during gamete formation and ends with the formation of zygote during fertilization where the diploid phase starts at the formation of a zygote by the fusion of two gametes and ends by meiotic cell division during gamete formation.

How many cells are produced in meiosis? The meiotic division produces four haploid cells from one diploid cell to complete the life cycle of sexually reproduced organisms such as humans and animals. Before meiosis, in the parent diploid cell, the chromosomal DNA duplicates, moreover, four haploid nuclei are formed as a result of two successive divisions of a diploid nucleus.

Why is meiosis important for organisms? Meiosis is biologically important since it is responsible for the genetic diversity among sexually reproduced organisms where during prophase I, the chromatids of the two homologous chromosomes synapse and exchange parts of their genetic materials.

Don’t Miss: Who Is Generally Recognized As The Founder Of American Psychology

What Is The Function Of Meiosis

Meiosis results in the reduction of chromosome number to half in gametes.

  • Meiosis is essential in the life cycle of all sexually reproducing organisms.
  • Maintenance of Chromosome number:Fertilization doubles the chromosome number during the fusion of two gametes.
  • Where in the human body does mitosis occur?

    In the human body, mitosis occurs in the nucleus of the bodys normal cells . It does not occur in gamete cells . Mitosis is a process that divides a single cell into two identical cells.

    What is the number of divisions in meiosis?

    In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells, each with half the number of chromosomes as the original parent cell. The two meiotic divisions are known as Meiosis I and Meiosis II.

    Late Prophase I Of Meiosis

    Meiosis

    Crossing over during Late Prophase I of Meiosis

    In late prophase I, the nuclear envelope completely breaks down and the spindle fibers attach at the kinetochores of the tetrads. Non-sister chromatids begin separating along several points along their length. Places where they stay connected are known as chiasmata. Chiasmata are where DNA was broken and rejoined between adjacent non-sister chromatids of homologous pairs. These chromosome segment exchanges are known as crossing over.

    Recommended Reading: What Is So3 In Chemistry

    State A Few Similarities Between Mitosis And Meiosis

    The similarities between mitosis and meiosis are as follows:

    • Mitosis and meiosis take place in the cell nuclei.
    • Both involve cell division.
    • Both the processes occur in the M-phase of the cell cycle.
    • In both cycles, the stages are common prophase, metaphase, anaphase and telophase.
    • Synthesis of DNA occurs in both.

    To know more about mitosis and meiosis, what is mitosis and meiosis, the difference between mitosis and meiosis, or any other topic in Biology, keep visiting BYJUS website or download the BYJUS app for further reference.

    Put your understanding of this concept to test by answering a few MCQs. Click Start Quiz to begin!

    Select the correct answer and click on the Finish buttonCheck your score and answers at the end of the quiz

    Meiosis I : Reductional Cell Division

    Sexual reproduction in organisms takes place through the fusion of male and female gametes, the sperm and the egg respectively. Gametes are haploid in nature, i.e., they contain only half the number of chromosomes. This genetic content makes them different from other body cells. Meiosis leads to the formation of haploid cells.

    Let us have a detailed look at meiosis 1 and the different stages and phases of meiosis 1.

    You May Like: What Is Locomotion In Biology

    Interaction Between The Spindle And Chromosomes

    Chromosomemicrotubule interactions in oocytes may be different from those in mitosis. In mitosis, the main interaction is provided by kinetochores, which interact with dynamic microtubule ends. In the simplest model of mitosis, microtubules nucleated from centrosomes capture kinetochores and generate pulling forces . When sister kinetochores are attached to microtubules from the opposite poles, chromosomes becomes congressed to the metaphase plate. The pulling forces acting between kinetochores and the opposite poles are resisted by cohesion among sister chromatids, and destruction of cohesin at the onset of anaphase triggers the movement of sister chromatids toward the poles. Although kinetochores are also important in meiosis, nonkinetochore interactions seem more prominent in oocytes than in mitotic cells.

    In Plants And Animals

    MEIOSIS A-Level Biology – How CROSSING OVER and INDEPENDENT SEGREGATION introduce genetic variation

    Meiosis occurs in all animals and plants. The end result, the production of gametes with half the number of chromosomes as the parent cell, is the same, but the detailed process is different. In animals, meiosis produces gametes directly. In land plants and some algae, there is an alternation of generations such that meiosis in the diploid sporophyte generation produces haploid spores. These spores multiply by mitosis, developing into the haploid gametophyte generation, which then gives rise to gametes directly . In both animals and plants, the final stage is for the gametes to fuse, restoring the original number of chromosomes.

    Read Also: What Does 4 Mean In Math

    What Are The 10 Phases Of Meiosis

    In this video Paul Andersen explains the major phases of meiosis including: interphase, prophase I, metaphase I, anaphase I, telophase I, cytokinesis, interphase II, metaphase II, anaphase II, and telophase II. He explains how variation is created in the next generation through meiosis and sexual reproduction.

    Metaphase I Of Meiosis

    In Metaphase I, all of the tetrads align along the metaphase plate. At this point, crossing over has completed, and the chromosomes are referred to as recombinant chromosomes. In your example, we are are only working with a single tetrad, so you are not able to visualize several tetrads aligning.

    Metaphase I of Meiosis

    You May Like: When To Round In Nursing Math

    Reductional And Equational Chromosome Segregation

    Homologous chromosomes are segregated in the first meiotic division, and sister chromatids are segregated in the second division. To achieve this, two major processes are specifically modified in meiosis in comparison with mitosis .

    Reductional and equational chromosome segregation. Cohesin connects sister chromatids. In mitosis, sister kinetochores are attached to microtubules from the opposite poles. Cohesin connects sister chromatids and the removal of cohesin along chromosomes triggers sister chromatid separation. Homologous chromosomes behave independently. In meiosis I, sister kinetochores are attached to microtubules from the same pole. Homologous chromosomes are attached to the opposite poles and connected by chiasma. Destruction of cohesin from chromosome arms triggers homologous chromosome separation. Cohesin at centromeres is protected to provide a linkage among sister chromatids. In meiosis II, sister kinetochores are attached to microtubules from the opposite poles. Destruction of the centromeric cohesin triggers sister chromatid separation.

    Telophase I And Cytokinesis

    Origins of Cell Compartmentalization

    In telophase, the separated chromosomes arrive at opposite poles. The remainder of the typical telophase events may or may not occur, depending on the species. In some organisms, the chromosomes decondense and nuclear envelopes form around the chromatids in telophase I. In other organisms, cytokinesisthe physical separation of the cytoplasmic components into two daughter cellsoccurs without reformation of the nuclei. In nearly all species of animals and some fungi, cytokinesis separates the cell contents via a cleavage furrow . In plants, a cell plate is formed during cell cytokinesis by Golgi vesicles fusing at the metaphase plate. This cell plate will ultimately lead to the formation of cell walls that separate the two daughter cells.

    Two haploid cells are the end result of the first meiotic division. The cells are haploid because at each pole, there is just one of each pair of the homologous chromosomes. Therefore, only one full set of the chromosomes is present. This is why the cells are considered haploidthere is only one chromosome set, even though each homolog still consists of two sister chromatids. Recall that sister chromatids are merely duplicates of one of the two homologous chromosomes . In meiosis II, these two sister chromatids will separate, creating four haploid daughter cells.

    You May Like: What Does Mks Stand For In Physics

    B Phases Of Meiosis Ii

    Interphase meiosis begins after the end of meiosis I and before the beginning of meiosis II, this stage is not associated with the replication of DNA since each chromosome already consists of two chromatids that were replicated already before the initiation of meiosis I by the DNA synthesis process. In brief, DNA is replicated before meiosis I start at one time only. The stage of meiosis II or second mitotic division has a purpose similar to that of mitosis where the two new chromatids are oriented in two new daughter cells. Therefore, the second meiotic division is sometimes referred to as .

    Step 1: Prophase II

    Prophase 2 is the stage that follows meiosis I or interkinesis, it is characterized by the nuclear envelope and nucleolus disintegration as well as the chromatids thickening and shortening in prophase II, and centrosomes replicate and migrate to the polar side. Prophase II is simpler and shorter than prophase I it somehow resembles the mitotic prophase. On the other hand, prophase II is different from prophase I since crossing over of chromosomes occurs during prophase I only and not prophase II. Metaphase II starts at the end of prophase II.

    Step 2: Metaphase II

    Metaphase 2 of meiotic division is also similar to metaphase of mitotic division, however, only half the number of chromosomes are present in metaphase II, metaphase II is characterized by the chromosomal alignment in the center of the cell.

    Step 3: Anaphase II

    Step 4: Telophase II

    Results of meiosis II

    The Process Of Meiosis

    In meiosis, there are a total of four stages. They are called prophase I, metaphase I, anaphase I and telophase I. The nucleus of a cell divides and leads to the production of haploid cells. Haploid cells are unlike the diploid cells as is the case in mitosis where the new cells have equal number of chromosomes as the mother or parent cell. In case of meiosis, there must be two cells in the beginning, both cells would halve the number of chromosomes and the nuclei of the two would get split leading to the formation of the two haploid cells. These haploid cells would then further lead to the formation of the new cell which will have the chromosomes of both the parent cells.

    Don’t Miss: What Is Brazil’s Geography

    Wise Removal Of Cohesin

    The second difference of meiosis from mitosis is stepwise removal of cohesin from chromosomes. Cohesin connects sister chromatids consisting of replicated DNA . In mitotic metaphase, cohesin resists the pulling forces acting on kinetochores toward the opposite poles. The cohesin complex is removed either by phosphorylation or cleavage of one of the subunits, Scc1. This removal triggers the separation of sister chromatids.

    In addition to the roles in meiosis, Sgo also has roles in ensuring the accuracy of chromosome segregation in mitosis . Although the molecular mechanism is still under investigation, evidence showed that it recruits and regulates various proteins at centromeres, including PP2A, the chromosomal passenger complex , and the microtubule-depolymerizing kinesin MCAK . The identification and subsequent studies of Sgo are a good example of how the studies of meiosis have made crucial contributions to the understanding of mitosis.

    Similarities Between Mitosis And Meiosis

    A Level Biology Revision “Stages of Meiosis”.
    • Both mitosis and meiosis take place in the cell nuclei, which can be observed under a microscope.
    • Both mitosis and meiosis involve cell division.
    • Both the processes occur in the M-phase of the cell cycle. In both cycles, the typical stages are prophase, metaphase, anaphase and telophase.
    • In both cycles, synthesis of DNA takes place.

    Also Read:

    Recommended Reading: What Is Net Migration In Geography

    How Do Cells Divide

    There are two types of cell division: mitosis and meiosis. Most of the time when people refer to cell division, they mean mitosis, the process of making new body cells. Meiosis is the type of cell division that creates egg and sperm cells.

    Mitosis is a fundamental process for life. During mitosis, a cell duplicates all of its contents, including its chromosomes, and splits to form two identical daughter cells. Because this process is so critical, the steps of mitosis are carefully controlled by certain genes. When mitosis is not regulated correctly, health problems such as cancer can result.

    The other type of cell division, meiosis, ensures that humans have the same number of chromosomes in each generation. It is a two-step process that reduces the chromosome number by halffrom 46 to 23to form sperm and egg cells. When the sperm and egg cells unite at conception, each contributes 23 chromosomes so the resulting embryo will have the usual 46. Meiosis also allows genetic variation through a process of gene shuffling while the cells are dividing.

    Mitosis and meiosis, the two types of cell division.

    Early Prophase I Of Meiosis

    Much like mitosis, Early Prophase I of meiosis begins with chromosomes condensing and the nuclear envelope beginning to disintegrate. Unlike prophase of mitosis, homologous chromosome pairs come together forming a tetrad, in which the four chromatids are connected along the length of each chromatid. Chromatids from different homologous pairs are referred to as non-sister chromatids.

    Don’t Miss: Theory Of Everything Geometry Dash 2

    Monopolar Attachment Of Sister Chromatids In Meiosis I

    The first difference of meiosis from mitosis is the behavior of kinetochores to achieve bipolar attachment. In mitosis, sister kinetochores must attach to the opposite poles. In contrast, in meiosis I, sister kinetochores must attach to the same pole and homologous kinetochores must attach to the opposite poles. This is the key division that reduces the ploidy of cells in meiosis. In meiosis II, like mitosis, sister kinetochores must attach to the opposite poles.

    In S. cerevisiae, the monopolin complex is responsible for monopolar orientation of sister kinetochores in meiosis I . The monopolin complex consists of casein kinase I and other regulatory subunits, and localizes to kinetochores in meiosis . Monopolin localization is dependent on Spo13, Polo kinase, and Cdc7 kinase .

    Why Does Meiosis Have 2 Divisions

    Cell Division

    From LM: Q1 = Cells undergoing mieosis require 2 sets of divisions because only half of the cromosomes from each parent are needed. This is so half of the offsprings genes come from each parent. This process generates the diversity of all sexually reproducing organisms. Meiosis produces sex cells eggs and sperm.

    Also Check: Flvs Geometry Module 3 Answers

    Faqs On Stages Of Meiosis

    1. How can students revise the chapter on Meiosis before an exam?

    All students can read from Stages of Meiosis – Definition, 6 Stages and FAQ on Vedantu. This page has explained what meiosis is and its stages well and can be used by the students to understand all the important concepts in a proper manner. All the useful information here is free of cost for the students and has been explained in simple terms. Only expert Biology teachers have contributed towards the study of Vedantu and so, it contains reliable inputs about the topics and sub-topics that it has.

    2. What is metaphase in Meiosis?

    Among the many different phases and stages of meiosis, metaphase is also a phase. It is a stage during the process of cell division. During the metaphase, the chromosomes condense and become distinguishable as they align in the center of the dividing cell.

    3. What are gametes?

    Gametes are used for the purpose of reproduction and are also known as sex cells. Thus, an organisms reproductive cells are termed gametes. Female gametes are called ova or egg cells and male gametes are called sperm.

    4. How many stages of meiosis are there?

    There are about six phases of meiosis. They are prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis. During prophase, differences from mitosis begin to appear and by the final phase i.e. cytokinesis, chromosome sets are split into two cells.

    5. Where can students find some questions on meiosis?

    7. Which Cells are Generated After Meiosis?

    The Phases Of Mitosis

    Prophase

    The first phase of mitosis is prophase. During prophase, the cells chromosomes condense and become visible under a light microscope. The nucleolus disappears, and the mitotic spindle begins to form.

    Prometaphase

    The nuclear membrane breaks down. The microtubules attach themselves to the chromosomes and begin to move them around.

    Metaphase

    The microtubules move the chromosomes until they are lined up along the middle of the cell. This line of chromosomes is called the metaphase plate.

    Anaphase

    The chromosomes are pulled apart by the microtubules. Each chromosome is separated into two, genetically identical sister chromatids, which are pulled to opposite ends of the cell.

    Telophase

    The sister chromatids arrive at opposite ends of the cell. A new nuclear membrane begins to form around each set of chromosomes. The chromosomes so they are no longer visible under a light microscope. The nucleolus reappears, and the mitotic spindle disappears.

    Finally, the cytoplasm of the cell splits, and two new, genetically identical daughter cells are formed. This process is called cytokinesis and usually takes place during telophase.

    Don’t Miss: Gina Wilson All Things Algebra 2014 Answer Key

    More articles

    Popular Articles