Each Phase of Mitosis has Unique Traits That Can be Identified Under a Microscope Or in a Micrograph
1. Prophase: The Preparation Stage
The first stage of mitosis, during which chromosomes condense and the mitotic spindle begins to form.
- Chromosome Condensation: Chromatin fibers coil tightly, making chromosomes visible as distinct structures.
- Sister Chromatids: Each chromosome consists of two identical sister chromatids joined at a centromere.
- Spindle Formation: Microtubules assemble into a spindle, a structure that will guide chromosome movement.
- Nuclear Envelope Breakdown: The nuclear membrane disintegrates, allowing spindle fibers to attach to chromosomes.
To identify prophase, look for thickened chromosomes and the disappearance of the nuclear envelope.
2. Metaphase: The Alignment Stage
The second stage of mitosis, during which chromosomes align at the cell's equator.
- Chromosome Alignment: Chromosomes line up along the cell’s equator, forming the metaphase plate.
- Spindle Attachment: Spindle fibers attach to the kinetochores, protein structures on the centromeres of each chromatid.
In metaphase, look for chromosomes neatly arranged in a line at the cell’s center.
3. Anaphase: The Separation Stage
The third stage of mitosis, during which sister chromatids are pulled apart to opposite poles of the cell.
- Chromatid Separation: Cohesin proteins holding sister chromatids together are cleaved, allowing them to separate.
- Movement to Poles: Spindle fibers shorten, pulling chromatids (now individual chromosomes) toward opposite poles.
- Don’t confuse anaphase with metaphase.
- In anaphase, the chromatids are clearly moving apart, whereas in metaphase, they are aligned in the center.
4. Telophase: The Reformation Stage
The final stage of mitosis, during which nuclear envelopes reform around the separated chromosomes.
- Nuclear Reformation: Nuclear envelopes reassemble around the two sets of chromosomes at each pole.
- Chromosome Decondensation: Chromosomes uncoil into chromatin, becoming less visible.
- Spindle Disassembly: The mitotic spindle breaks down.
Telophase is often accompanied by cytokinesis, the division of the cytoplasm, which begins to form two separate daughter cells.
Identifying Mitosis Under the Microscope
When observing cells under a microscope or in a micrograph, use these key features to identify each phase:
- Prophase: Thickened chromosomes, no visible nuclear envelope.
- Metaphase: Chromosomes aligned at the cell’s equator.
- Anaphase: Chromatids moving toward opposite poles.
- Telophase: Re-forming nuclear envelopes and decondensing chromosomes.
- How does the ability to identify mitotic phases enhance our understanding of growth and development in living organisms?
- Consider how this knowledge might be applied in fields like medicine or agriculture.
- Can you identify the phase of mitosis in a micrograph?
- What key features would you look for in each phase?
