Biology – Chromosome behaviour in mitosis | e-Consult
Chromosome behaviour in mitosis (1 questions)
The spindle apparatus is a crucial structure in mitosis, responsible for the accurate segregation of chromosomes into daughter cells. It is composed of microtubules, which are protein filaments that polymerize and depolymerize to form the spindle. The spindle originates from the centrosomes, which are microtubule-organizing centers located near the poles of the cell.
Structure of the Spindle: The spindle consists of several types of microtubules:
- Kinetochore microtubules: These microtubules attach to the kinetochores of the chromosomes.
- Polar microtubules: These microtubules overlap in the middle of the cell and help to maintain cell polarity.
- Astral microtubules: These microtubules radiate outwards from the centrosomes and attach to the cell cortex.
Chromosome Segregation: The spindle ensures accurate chromosome segregation through a complex interplay of forces. Kinetochore microtubules exert pulling forces on the chromosomes, moving them towards the poles. Polar microtubules push the poles apart, elongating the cell. Astral microtubules help to position the spindle correctly and maintain cell stability. The spindle checkpoint ensures that all chromosomes are correctly attached to the spindle before anaphase begins, preventing errors in chromosome segregation.
Differences between Animal and Plant Spindles:
| Feature | Animal Cell | Plant Cell |
| Centrosomes | Two centrosomes, located near the poles. | No centrosomes; spindle forms within the nucleus. |
| Astral microtubules | Absent. | Present; attach to the cell cortex. |
| Cytokinesis | Cleavage furrow formation. | Formation of a phragmoplast to build a new cell wall. |