chromosome segregation

Definition

Target type: biologicalprocess

The process in which genetic material, in the form of chromosomes, is organized into specific structures and then physically separated and apportioned to two or more sets. In eukaryotes, chromosome segregation begins with the condensation of chromosomes, includes chromosome separation, and ends when chromosomes have completed movement to the spindle poles. [GOC:jl, GOC:mah, GOC:mtg_cell_cycle, GOC:vw]

Chromosome segregation is a fundamental process in cell division, ensuring that each daughter cell receives a complete and identical set of chromosomes. This intricate process involves the orchestrated movement of duplicated chromosomes, each comprised of two sister chromatids, to opposite poles of the cell. The accuracy of chromosome segregation is critical for maintaining genome integrity and preventing genetic disorders. The process can be broadly divided into several key stages:

1. **Chromatin Condensation and Sister Chromatid Cohesion:** Prior to segregation, DNA undergoes condensation, packaging the long, linear chromosomes into compact structures. This compaction facilitates efficient chromosome movement. Simultaneously, sister chromatids, the two identical copies of a chromosome produced during replication, remain tightly linked together through cohesion proteins.

2. **Spindle Formation:** The mitotic spindle, a dynamic microtubule-based structure, forms from the centrosomes, microtubule-organizing centers located near the cell's poles. Microtubules emanate from the centrosomes and interact with chromosomes, guiding their movement.

3. **Chromosome Attachment and Alignment:** Microtubules from opposite poles attach to specialized regions on chromosomes called kinetochores, which are assembled at the centromere, the constricted region of the chromosome. Kinetochores act as molecular motors, facilitating the movement of chromosomes towards the poles. During this stage, chromosomes align at the metaphase plate, an imaginary plane equidistant from the two poles of the spindle. This alignment ensures that each daughter cell will inherit a complete set of chromosomes.

4. **Sister Chromatid Separation:** At the onset of anaphase, the cohesion proteins that hold sister chromatids together are cleaved, allowing the chromatids to separate. Simultaneously, the spindle poles move further apart, pulling the chromatids towards opposite poles of the cell. This movement, driven by the dynamic assembly and disassembly of microtubules, is crucial for achieving proper chromosome segregation.

5. **Decondensation and Nuclear Envelope Formation:** Once chromosomes reach the poles, they decondense, returning to their less compact, relaxed state. Nuclear envelopes reform around the chromosomes, creating distinct nuclei within the daughter cells.

6. **Cytokinesis:** As the nuclear division concludes, the cytoplasm divides, separating the two daughter cells. This process is often initiated during anaphase and completes shortly after nuclear division. In animal cells, a contractile ring composed of actin filaments pinches off the cell membrane, creating two separate cells. In plant cells, a cell plate forms from the inside out, eventually creating a new cell wall that divides the cell.

These steps are intricately regulated by a complex interplay of proteins, including motor proteins, microtubule-associated proteins, and signaling molecules. These proteins ensure that chromosomes are correctly attached, aligned, and separated with precision. Errors in chromosome segregation can result in aneuploidy, a condition where cells have an abnormal number of chromosomes, leading to various genetic disorders and diseases.'
"

Proteins (24)

Compounds (460)