Cell Division: Mitosis and Meiosis
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Cell Division

Cell division is one of the most fascinating and dramatic processes in living organisms. From the smallest to the largest, all organisms undergo cell division. In multicellular organisms, it is essential for growth, tissue repair, and cell replacement.

Mitosis

Occurs in somatic cells, driving growth (e.g., a baby developing into a teenager) and healing (e.g., repairing a cut).

Meiosis

Occurs in the ovaries and testes, producing gametes (sperm and egg cells) for reproduction.

Interphase: Preparation for Cell Division

During interphase, chromosomes exist as chromatin—a thin, fibrous form of DNA wound around histone proteins. After interphase, chromatin condenses into compact sister chromatids, facilitated by the condensin protein complex.

Discover the Fascinating Process of Cell Division

From the smallest to largest organisms, all living things undergo cell division. Explore how cells multiply through mitosis and meiosis to enable growth, repair, and reproduction.

Learn About Mitosis Explore Meiosis

Mitosis

The process of cell division that results in two genetically identical daughter cells. Essential for growth and repair in multicellular organisms.

Meiosis

A special type of cell division that produces gametes (sex cells) with half the number of chromosomes, enabling sexual reproduction.

Interphase

The preparatory phase where the cell grows, replicates its DNA, and prepares for division. Includes G1, S, and G2 phases.

Three Phases of Interphase

1

First Gap Phase (G₁ Phase)

The primary growth period following cytokinesis and preceding DNA synthesis. The cell grows, synthesizes proteins, and produces organelles.

2

Synthesis Phase (S Phase)

DNA replication occurs, duplicating chromosomes into sister chromatids. Histones and other materials vital for chromosome replication are synthesized.

3

Second Gap Phase (G₂ Phase)

Bridges DNA synthesis and cell division. Cells synthesize organelles and materials crucial for division.

Mitotic Phase: Cell Division

Cells in the body are constantly replaced through division—bone cells create new bone cells, skin cells generate new skin cells. At this moment, thousands of cells are being renewed.

Rapid Division

Skin cells, red blood cells

Slow Division

Nerve cells, brain cells

Non-Dividing

Muscle cells (grow without dividing)

Somatic Cells

Diploid (2n)

46

46 chromosomes in humans

Germ Cells

Haploid (n)

23

23 chromosomes in gametes

Mitosis

Mitosis is a type of cell division in which two identical daughter cells are produced from a single parent cell. Mitosis involves four phases: prophase, metaphase, anaphase, telophase. At the end of telophase, two diploid cells containing the same set of chromosomes from the parent cell are produced. Cytokinensis is the physical division of the cytoplasm of a parent cell into two. This process occurs concurrently with the latter stages of mitosis. In animal cells, cytokinesis involves the formation of a cleavage furrow , which pinches off or divides the cell into two. In plants, instead of being cleaved, a cell plate forms between the two nuclei. The cell plate enlarges and elongates until it merges with the cell walls, and eventually forms a new cell wall.

Mitosis: Cell Division for Growth and Repair

Mitosis is the process by which somatic (body) cells divide to produce two identical daughter cells. This ensures that each new cell receives an exact copy of the parent cell's genetic material

1Prophase

Chromatin condenses into chromosomes, nuclear membrane breaks down, spindle fibers form.

2Metaphase

Chromosomes align at the cell's equator, attached to spindle fibers at their centromeres.

3Anaphase

Sister chromatids separate and move to opposite poles of the cell.

4Telophase

Nuclear membranes reform, chromosomes decondense, cytokinesis divides the cytoplasm.

Mitosis Visual Guide

1
Prophase
2
Metaphase
3
Anaphase
4
Telophase

Meiosis: Production of Gametes

Meiosis involves two successive cell divisions (Meiosis I and II) that reduce the chromosome number by half, producing four genetically unique haploid cells.

IProphase I

Homologous chromosomes pair up (synapsis) and may exchange genetic material (crossing over).

IMetaphase I

Homologous chromosome pairs align at the metaphase plate as tetrads.

IAnaphase I

Homologous chromosomes separate and move to opposite poles (sister chromatids remain attached).

ITelophase I

Two haploid cells form, each with duplicated chromosomes (sister chromatids).

IIProphase II

Spindle apparatus forms in each haploid cell from Meiosis I.

IIMetaphase II

Chromosomes align at the equator in each haploid cell.

IIAnaphase II

Sister chromatids separate and move to opposite poles.

IITelophase II

Nuclear membranes reform, resulting in four genetically unique haploid gametes.

Meiosis Phases: Detailed Visual Guide

Click on any image to view it larger with detailed description

Interphase: Preparation for Meiosis

Interphase in Meiosis

Before entering meiosis, cells undergo interphase with three distinct phases:

G₁ Phase

Cell growth, synthesis of RNA and proteins

S Phase

DNA replication, chromosome duplication

G₂ Phase

Final preparation, synthesis of proteins needed for division

Meiosis I: Reduction Division

1
Prophase I

Prophase I

  • Chromosomes condense and pair up (synapsis)
  • Crossing over occurs at chiasmata
  • Nuclear envelope breaks down
2
Metaphase I

Metaphase I

  • Homologous pairs align at metaphase plate
  • Independent assortment occurs
  • Spindle fibers attach to centromeres
3
Anaphase I

Anaphase I

  • Homologous chromosomes separate
  • Sister chromatids remain attached
  • Chromosomes move to opposite poles
4-5
Telophase I and Cytokinesis

Telophase I & Cytokinesis

  • Nuclear envelopes reform
  • Chromosomes decondense
  • Cytoplasm divides forming two haploid cells

Meiosis II: Equational Division

1
Prophase II

Prophase II

  • Chromosomes recondense
  • Nuclear envelope breaks down
  • Spindle apparatus forms
2
Metaphase II

Metaphase II

  • Chromosomes align single file at equator
  • Centromeres divide
  • Spindle fibers attach to each chromosome
3
Anaphase II

Anaphase II

  • Sister chromatids separate
  • Chromatids (now chromosomes) move to poles
  • Complete set of chromosomes at each pole
4-5
Telophase II and Cytokinesis

Telophase II & Cytokinesis

  • Nuclear envelopes reform
  • Chromosomes decondense
  • Cytoplasm divides forming four haploid gametes

Final Result of Meiosis

Thus at the end of meiosis II, four non-identical, haploid daughter cells are formed, each having half chromosome number as the original parent cell.

Mitosis vs. Meiosis

Feature Mitosis Meiosis
Cell Type Somatic cells (body cells) Reproductive cells (gametes)
Number of Divisions One Two (Meiosis I and II)
Daughter Cells Produced Two diploid cells Four haploid cells
Chromosome Alignment Single file at metaphase Homologous pairs (tetrads) in Meiosis I
Genetic Variation None (identical to parent) Yes (crossing over and independent assortment)
Purpose Growth, repair, asexual reproduction Sexual reproduction (gamete formation)

The Stages of Mitosis

1

Interphase

Cell prepares for division, DNA replicates

2

Prophase

Chromatin condenses into chromosomes

3

In Late Prophase

Starts to Catch and put Together the Chromosomes

4

Metaphase

Chromosomes align at cell equator

5

Anaphase

Sister chromatids separate to poles

6

Telophase

Nuclear membranes reform

7

Cytokinesis

Cytoplasm divides into two cells

References

Textbooks

  • RBS Science and Technology Series Science Links 8 Lesson 13.1: The Cell cycle and Stages of Mitosis p.420 Lesson 13.2: Meiosis- Reproduction Of Gametes p.426 Revised Edition ISBN 978-621-04-4673-9 Classification: Worktext (03-SB-00133-0) Reprinted: February 2023
  • Science in Today's World Updated and Revised Edition 8 Chapter 14 Cellular Reproduction p.184-191 Copyright 2022 By Sibs Publishing House, Inc. Eden Vela-Evangelista, et al.

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