How can the phases of mitosis be identified in cells viewed under a microscope or in a micrograph?

SouravNovember 7, 2024

Answer

Identifying the phases of mitosis in cells viewed under a microscope or in micrographs involves recognizing distinct morphological changes that occur during each phase. Here’s a detailed guide on how to identify these phases:

Phases of Mitosis

1. Prophase

• Characteristics:
  • Chromatin condenses into visible chromosomes, each consisting of two sister chromatids joined at the centromere.
  • The nuclear envelope begins to break down, and the nucleolus disappears.
  • The mitotic spindle starts to form as centrosomes move to opposite poles of the cell.
• Identification: Under the microscope, look for:
  • Thick, distinct chromosomes that are not yet aligned.
  • Disappearance of the nucleolus and signs of the nuclear envelope breaking down.

2. Prometaphase

• Characteristics:
  • The nuclear envelope completely disintegrates, allowing spindle fibers to attach to kinetochores on the chromosomes.
  • Chromosomes continue to condense and become more distinct.
• Identification: This phase is often harder to distinguish but can be identified by:
  • Chromosomes that are still visible but are now clearly interacting with spindle fibers.
  • Movement of chromosomes as they are being positioned for alignment.

3. Metaphase

• Characteristics:
  • Chromosomes align along the metaphase plate (the cell’s equatorial plane).
  • Each chromosome is attached to spindle fibers from opposite poles.
• Identification: Look for:
  • A clear line of chromosomes positioned in the center of the cell, with sister chromatids facing opposite poles.
  • Spindle fibers extending from centrosomes to kinetochores.

4. Anaphase

• Characteristics:
  • Sister chromatids are pulled apart at the centromere and move toward opposite poles of the cell.
  • The cell elongates as non-kinetochore microtubules push against each other.
• Identification: Under the microscope, you will see:
  • Chromatids separating and moving toward opposite ends of the cell, appearing as two distinct groups.
  • The cell shape may start to elongate.

5. Telophase

• Characteristics:
  • Chromosomes arrive at opposite poles and begin to decondense back into chromatin.
  • Nuclear envelopes reform around each set of chromosomes, and nucleoli reappear.
• Identification: Look for:
  • Two distinct nuclei forming within the same cell, with less condensed chromatin compared to prophase.
  • The presence of a reformed nuclear envelope surrounding each nucleus.

Cytokinesis (Not a Phase of Mitosis but Important)

• Following telophase, cytokinesis occurs, which is the physical division of the cytoplasm into two daughter cells.
• In animal cells, this is characterized by the formation of a cleavage furrow; in plant cells, a cell plate forms.

Observational Techniques

1. Staining: Using stains like acetocarmine or DAPI can help visualize chromosomes more clearly by highlighting DNA. This makes it easier to distinguish between different phases based on chromosome visibility and organization.
2. Microscopy: Using a light microscope with appropriate magnification (e.g., 40x) allows for clear observation of cellular structures. Fluorescence microscopy can also be employed for enhanced visualization of specific components like microtubules and chromosomes.
3. Micrographs: Analyzing micrographs can help identify phases based on chromosomal arrangement and cellular morphology. Look for characteristic features such as alignment along the metaphase plate or separation during anaphase.