The diagram of meiosis helps us understand the process of cell division and the formation of gametes (sex cells) with half the number of chromosomes as the parent cell. The diagram of meiosis class 9 is an important question that is often asked in examinations. The meiosis diagram with explanation is given here.
The labelled simple diagram of meiosis is given below:
Table of Content
What is Meiosis?
Meiosis is a type of cell division that occurs in sexually reproducing organisms. It is a crucial process where a single cell divides twice, resulting in the formation of four cells, each with half the number of chromosomes as the original cell. These new cells are called gametes, such as sperm and egg cells in animals, or pollen and ovules in plants. Meiosis ensures genetic diversity in offspring by shuffling and recombining genetic information from the parent cells.
Meiosis has a long prophase in the first meiotic division where the homologous chromosomes are close to each other and the genetic material is exchanged. Similarly, the number of chromosomes decreases during the first meiosis, resulting in two haploid cells. The term heterotypic division can also be used to describe an early meiotic division.
Also Read: Mitosis
Meiosis Stages
As seen in the diagram of meiosis, it is a two-step process in which cells are divided, called meiosis I and II. The cytoplasmic division is part of every step in the process. Meiosis I and meiosis II each have the following 4 steps: Prophase, metaphase, anaphase, telophase, and cytokinesis. Interphase is an initial phase of cell division followed by other steps in meiosis.
Interphase
The interphase is the initial phase like mitosis. During interphase, the nuclear envelope stays intact, with chromosomes appearing as a diffuse, long, coiled, and faintly visible filament of chromatin. There’s a doubling in the amount of DNA. The nucleolus size is significantly increased because of the accumulation of rRNA and ribosomal proteins. In animals, a new pair of centrioles forms near the present centriole, and this results in two pairs of centrioles within an interphase cell.
A major change takes place in the G2 stage of interphase, with a cell heading toward meiosis instead of mitosis. When the first meiosis division starts, the nucleus is born by absorbing some of the water in the cytoplasm and increasing its size by about three times.
Meiosis I
This process is visually represented in the meiosis diagram above. The meiosis is divided into two sub part Meiosis I and meiosis II.
Prophase I
- Leptotene: Chromosomes uncoil, resembling thread-like shapes with bead-like structures called chromomeres. Chromosomes are directed toward centrioles, creating a bouquet appearance (Bouquet Stage).
- Zygotene or Synaptotene: Synapsis i.e. pairing of homologous chromosomes begins. A synaptonemal complex stabilizes pairing and facilitates recombination or crossing over. Synapsis can start at various points along chromosomes (pro terminal synapsis), end at centromeres (pro-centric pairing), or at random points.
- Pachytene: The chromosomes are twisted around each other, becoming indistinguishable. Each of the homologous chromosomes splits lengthwise and forms two chromatids connected by a common centromere. It forms bivalent or tetrad Chromosomes. The exchange of genetic material between homologous chromosomes is an important step in crossing over. An endonuclease enzyme breaks down non-sister chromatids at the crossing-over site. Interchange of chromatid segments occurs between non-sister chromatids, facilitated by ligase.
- Diplotene: The synaptonemal complex has dissolved and the chromatids are physically joined to each other at its specific points, called chiasmata. Chiasmata are moving in a zipperlike way toward the chromosome’s end.
- Diakinesis : Bivalent chromosomes become more compact and evenly distributed in the nucleus. The nuclear envelope’s going to break down, the nucleolus’s going to disappear. Chiasmata are reaching the ends of chromosomes, while chromatids continue to stay attached until metaphase.
Metaphase I
- The spindle fibers are attached to the chromosomes.
- Chromosomes are located at the equator.
- Spindle fibers connect to centromeres of homologous chromosomes, directed toward opposite poles.
Anaphase I
- Homologous chromosomes divide and move to the opposite poles.
- Chromosomal fibers or microtubules shorten, pulling each chromosome with two chromatids and an undivided centromere.
- The formation of chiasma results in nongenetically related chromatids on a chromosome.
Telophase I
- Chromosomes move to opposite poles.
- In the vicinity of the chromosomes, a new nuclear envelope forms.
- Chromosomes relax, and nucleolus reappear.
- Two daughter nuclei are created.
Cytokinesis I
- Cell membrane constriction divides cells in animals, whereas in plants a cell plate forms to form two daughter cells.
Meiosis II
Haploid cells are dividing mitotically in the second stage of Meiosis. There are four haploid cells produced. Just like the first meiotic division, this one is called homotypic and it does not involve exchanging genetic material or cutting down chromosome numbers. The above given meiosis diagram shows these steps clearly.
Prophase II
- Centrioles divide into two pairs.
- The pairs move to the opposite poles and the nuclear membrane disappears.
Metaphase II
- Chromosomes are aligned with the cell equator by spindle fibers.
- Centromeres split up to form a pair of daughters’ chromosomes.
- Each chromosome’s centromere is attached by fibers of the Spindle.
Anaphase II
- Daughter chromosomes move to opposite poles.
- The microtubules of chromosomes are shortening and those of Interzonal Microtubules are tightening.
Telophase II
- Chromatids are transformed into chromosomes and shift to the opposing poles.
- The nuclear envelope is composed of the endoplasmic reticulum.
- The nucleolus arises as a result of ribosomal RNA synthesis.
Cytokinesis II
- The cytoplasm divides and produces four of its daughter cells, similar to cytokinesis I.
Conclusion – Diagram of Meiosis
The diagram of meiosis are a vital tool in learning the detailed process of cell division, particularly in the formation of gametes with reduced chromosome numbers. The meiosis diagram is often asked in the examination so it is important to have your concepts clear. The process of meiosis is important for maintaining genetic diversity in offspring. The process involves two main stages: Meiosis I and Meiosis II, each consisting of prophase, metaphase, anaphase, telophase, and cytokinesis.
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FAQs on Meiosis Diagram
What is Meiosis?
The process of eukaryotic cell division that forms four haploid cells in a sexually reproducing organism is termed meiosis.
What are the Two Main Steps of Meiosis?
Meiosis occurs in two cycles which involve meiosis I and meiosis II. The cell division starts with interphase. Meiosis I and meiosis II each cycle involve Prophase, metaphase, anaphase, telophase, and cytokinesis.
Why Meiosis Occurs only in Sexually Reproducing Animals?
The main function of meiosis is gamete or sex cell production. Hence, meiosis occurs only in sexually reproducing animals.
What is Meiosis with a Diagram?
Meiosis is a type of cell division that creates reproductive cells with half the number of chromosomes, ensuring genetic diversity. A diagram illustrates the process, showing how one cell divides twice to produce four haploid cells.
What is the Structure of Meiosis?
Meiosis consists of two main stages: Meiosis I and Meiosis II. During Meiosis I, homologous chromosomes pair up and exchange genetic material, resulting in genetic diversity. In Meiosis II, sister chromatids separate, producing four haploid cells.