What is Karyokinesis?

Karyokinesis is the process of nuclear division that occurs during cell division mitosis or meiosis, specifically in eukaryotic cells. It is the first step in the M phase of the cell cycle. It is followed by cytokinesis, which is the splitting of the cytoplasm and cell membrane. Karyokinesis is divided into five phases Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis.

The process of karyokinesis allows the growth and expansion of multicellular organisms. It also enables the regeneration of damaged tissues. In this article, we will study Karyokinesis, the stages of karyokinesis, its significance, and the difference between karyokinesis and cytokinesis.

Definition of Karyokinesis

Kayokinesis is a process where the nucleus divides to create two daughter nuclei during cell divison. It is followed by cytokinesis. 

What is Karyokinesis?

Karyokinesis is a process where the nucleus splits into two daughter nuclei during cell division. W. Schleicher coined the term “karyokinesis” in 1878. The term “karyokinesis” is derived from the Greek words “karyon,” meaning “nucleus” and “kinesis,” meaning “movement”. It is the first step of the cell cycle. Karyokinesis occurs only in cells that are in the G0 phase of interphase. During karyokinesis, DNA condenses and chromosomal material splits into two equal halves and line up in the middle of the cell.

The chromosome divide equally between the two new nuclei. The phases of karyokinesis include prophase, metaphase, anaphase, and telophase. Karyokinesis is followed by cytokinesis, which is the splitting of the cytoplasm and cell membrane. The purpose of mitosis is cell growth and to replace or regenerate damaged cells or tissues.

Karyokinesis Diagram

The diagram of karyokinesis showing different stages are as follows:

Karyokinesis Phases

Karyokinesis involves the division of a cell nucleus during mitosis or meiosis. The two main types of karyokinesis are mitosis and meiosis. The stages of Karyokinesis include:

1. Prophase

Prophase is the initial stage of both mitosis and meiosis. It is the longest phase and is divided into two phases:

• Early prophase
• Late prophase

Early Phase

• It is the first stage of mitosis that follows the S and G2 phases of interphase.
• Chromatin fibers begin to condense into visible chromosomes.
• The mitotic spindle starts forming.
• Centrioles duplicate and move to the opposite poles of the cell.

Late Phase

• It is also known as prometaphase.
• The nuclear envelope breaks down completely.
• The spindle fibers attach at the kinetochores of the tetrads.
• Centrosomes are positioned at opposite poles, establishing the bipolar spindle apparatus.

2. Metaphase

It is the second stage of the mitosis that follows prophase. It is also known as metakinesis.

• Chromosomes align at the cell’s equator, forming the metaphase plate.
• The chromosomes are at their second-most condensed and coiled stage during metaphase.
• Spindle fibers from opposite poles attach to the kinetochore of each chromosome.
• Chromosomes are positioned for equal distribution to daughter cells in the upcoming anaphase.

3. Anaphase

Anaphase is the fourth phase of the mitosis. It is characterised by chromosome s moving towards opposite pole of the cell.

• Kinetochore microtubules shorten.
• Non-kinetochore microtubules lengthen.
• Centrosomes are pushed far apart and the cell elongates as spindle fibers continue to separate chromatids.
• This phase ensure that each daughter cell receives a complete set of chromosomes for genetic stability.

4. Telophase

Telophase is the fifth and last stage of karyokinesis. It is usually followed by cytokinesis, in which the cytoplasm is physically divided to form two daughter cells.

• It starts when the replicated, paired chromosomes have been separated and pulled to opposite sides, or poles, of the cell.
• The decondensation of chromosomes starts.
• The spindle starts disappearing.
• The nuclear envelope assembly around each set of chromosomes.
• Telophase is usually followed by cytokinesis.

Karyokinesis Meiosis

Meiosis consists of two successive cell divisions, known as meiosis I and meiosis II:

Meiosis I

• Prophase I: Chromosomes condense, and homologous chromosomes undergo genetic recombination (crossing over).
• Metaphase I: Homologous chromosomes align at the cell’s equator.
• Anaphase I: Homologous chromosomes separate and move to opposite poles.
• Telophase I: Two haploid cells are formed, each with half the chromosome number of the original cell.

Meiosis II: Similar to mitosis, resulting in the formation of four non-identical haploid daughter cells.

Significance of Karyokinesis

Karyokinesis plays an important role in the cell division, in growth, development and reproduction of eukaryotic organisms. Significance of karyokinesis are:

• It ensures the accurate distribution of genetic material including chromosomes to daughter cells during cell division.
• It help in maintaining genetic stability and preserving the species-specific information encoded in the DNA.
• The process is fundamental for growth, tissue repair, and the maintenance of the organism’s overall structure.
• It is important for living organisms because it ensures that cells can regenerate. 
• It ensures that cells and tissues can mature, create, and redevelop within a finite time.

Disturbances of Karyokinesis

Karyokinesis is nuclear division. Disturbances of karyokinesis can include:

• Collapse of prophase
• Failure of cytokinesis
• Alterations of multicentric spindles
• Destruction of the tubulin cytoskeleton
• Alterations of spindle formation
• Inadequate development of the mitotic apparatus.

Difference Between Karyokinesis and Cytokinesis

The difference between Karyokinesis and Cytokinesis are as follows:

Feature	Karyokinesis	Cytokinesis
Definition	Division of the cell nucleus, involving chromosomes.	Division of the entire cell, including the cytoplasm.
Occurs in	Both eukaryotic mitosis and meiosis.	Follows karyokinesis in mitosis and meiosis.
Nature	Nuclear division.	Cytoplasmic division.
Process	Involves the separation of chromosomes into daughter cells.	Involves the division of the cytoplasm and organelles.
Timing	Precedes cytokinesis.	Follows karyokinesis.
Purpose (Mitosis)	Formation of two identical daughter nuclei.	Formation of two identical daughter cells.
Purpose (Meiosis)	Formation of four non-identical haploid daughter cells.	Meiosis involves two rounds of karyokinesis.
Result	Two daughter nuclei with the same genetic material.	Two daughter cells with the same genetic material.
Components Affected	Nucleus and chromosomes.	Cytoplasm, organelles, and cell membrane.
Location in the Cell Cycle	Occurs during the M phase (mitosis and meiosis).	Typically occurs immediately after karyokinesis.
Cellular Outcome	Determines the genetic makeup of daughter cells.	Establishes two separate, fully functional cells

FAQs on Karyokinesis

1. What is Karyokinesis?

Karyokinesis is the process of cell division where the nucleus splits to create two daughter nuclei. It can can occur during mitosis or meiosis.

2. What is the Process of Cytokinesis and Karyokinesis?

Cytokinesis is the process of cell division where the cytoplasm of a parent cell divide into two daughter cells while Karyokinesis is the process of cell divison where nucleus of parent cell divide into two daughter nuclei.

3. What are the 4 stages of Karyokinesis?

Karyokinesis is divided into four stages including prophase, metaphase, anaphase and telophase. The process of karyokinesis is followed by cytokinesis.

4. What is the First Stage of Karyokinesis?

The fisrt stage of the karyokinesis is prophase. It is the longest phase of the cell cycle and is characterised by condensation of chromosome, spindle fibre formation and the nuclear envelope breaks down.

5. What is the Last Stage of Karyokinesis?

Final stage of the karyokinesis is Anaphase. It is the shortest phase and is characterised by separation of sister chromatid that move towards opposite poles of the cell, caused by shortening of spindle fibre.