Metaphase I and Metaphase II

The Cell cycle can be defined as the duplication and division of contents into two parts. It is an essential mode by which organisms can reproduce. Though the cell cycle is the basic mechanism to divide, it possesses the characteristic of passing on the hereditary characters to the progeny in an ordered sequence. For the production of identical daughter cells genetically, it must follow the process of replication. Replication is an errorless procedure to pass the genetic information to the coming generation. It is completed in two phases Interphase and Metaphase. In this article, we will mainly focus on the subdivisions of Metaphase, including Metaphase I and Metaphase II, which is called the division phase. The chromosomes which have been replicated go for segregation in two daughter cells, where they get the copies of the genome. Apart from this receiving of the genome, duplication of various organelles and macromolecules takes place by increasing their cell mass. 

Note: 

  1. Just after birth, neural cells stop their division. 
  2. In 1953 Howard and Pele described The Cell cycle. 
  3. In 1841 Remak said the term Amitosis- a can be defined as the process of division that occurs directly means no spindle formation nor the chromosome’s appearance takes place. It is a rare process. Example: division in Paramecium 
  4. In 1975 Eduard Strasburger described the process of mitosis in plant cells.
  5. In 1882 Walther Flemming described the term mitosis in animal cells.
  6. Karyokinesis: The term karyokinesis can be defined as the division of a nucleus.
  7. Cytokinesis: The term cytokinesis can be defined as the division of cytoplasm.
  8. The other name of Kinetochores is tractile fibres. 
  9. In 1887 Schneider introduced the term karyokinesis. 
  10.  In 1887 Whiteman introduced the term cytokinesis. 
  11. Other names for The Cell equator include the Metaphase plate and the Equatorial plate. It is a region present equidistant from the two poles in a cell, the division phase.

Interphase: 

Interphase,/ is a phase that is considered the resting phase.

Resting cells cannot be considered as in the cell cycle. No resting phase occurs. When a cell is not dividing, it is regarded as a powerhouse as it remains active metabolically throughout. It is considered to be the longest phase. In this phase, the synthesis of mRNA and rRNA takes place. 

Sub stages of Interphase include: 

  • G1 Phase (Post Mitotic Phase)
  • S Phase (Synthesis Phase)
  • G2 Phase (Pre Mitotic Gap Phase)

Metaphase:

Metaphase is a subdivision of the mitotic phase or equatorial division where karyokinesis and cytokinesis occur, respectively, so that the exact genome of the parent can be transferred to the Filial generations and so on. It is a phase in which a condensed form of DNA is visible in the form of chromosomes. M stage of the cell cycle can occur in both somatic and germinal cells. Metaphase occurs in eukaryotes. 

 Characteristics of Metaphase:

  • Simple and short
  • It takes 10 minutes to complete and minimally takes 2 minutes to complete.

Events of Metaphase:

  • The Movement of spindle fibre takes place in the nucleus. 
  • Movement of chromosomes shifts towards the equatorial plane of the spindle fibres.
  • Extension of spindle fibres occurs in the form of chromosomes by attaching themselves to the kinetochores.
  • From each pole of the spindle fibres, there is a joining of two fibres of chromosomes.
  • Extension of spindle fibres takes place from the pole by detaching themselves to the chromosomes and is considered as. Non-kinetochores. Overlapping can occur in some of them at the equator. 
  • Arrangement of chromosomes in the form of a plate at the equator called the metaphase plate.
  • Congression: The phenomenon of architecting chromosomes on the spindle of the equator is termed congression. 

Prometaphase: 

Events or processes of connecting the chromosomes to the spindle fibres by bringing them to the metaphase plate are termed prometaphase. 

Metaphase I:

Characteristics of metaphase I:

  • Shifting of spindle fibres takes place. 
  • The Shifting of tetrads takes place from the equator to in mid of the metaphase plates, which carry n chromosomes in the form homologous of each other.
  • Homologous chromosomes have kinetochores by which spindle fibres are attached. 
  • The main events of Metaphase I occur in Meiosis I.

Metaphase II: 

Characteristics of Metaphase II:

  • Chromosomes shift to the equator of spindle fibres.
  • One plate of metaphase is formed.
  • Like mitosis, an extension of chromatids with their respective chromosomes occurs.
  • The main event of Metaphase II occurs in meiosis II.

Other substages of the M phase include:

  • Prophase
  • Anaphase 
  • telophase

Conclusion: 

The Cell cycle can be defined as the duplication and division of contents into two parts. Though the cell cycle is the basic mechanism to divide, it possesses the characteristic of passing on the hereditary characters to the progeny. Cell division and Cell Regulation is the basic process for the multiplication and design of the cell to increase their size. The process of cell division leads to the development of the embryo, growth, reproduction, maintenance, and repair by carrying out the proper functioning of central dogma. Anyone’s improper functioning can lead to cancer. 

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