Metaphase
Metaphase is the stage of cell division in which chromosomes reach maximum condensation and align along the cell's equatorial plane, known as the metaphase plate, pulled by spindle fibers attached to each chromosome's centromere. This precise alignment ensures that when sister chromatids separate, each daughter cell receives exactly one copy of every chromosome. Metaphase is used in karyotyping because chromosomes are most visible and identifiable at this stage.
Metaphase Characteristics in Mitosis vs Meiosis
| Characteristic | Metaphase (Mitosis) | Metaphase I (Meiosis) | Metaphase II (Meiosis) |
|---|---|---|---|
| Units at plate | Individual chromosomes | Homologous pairs (bivalents) | Individual chromosomes |
| Spindle attachments | 2 per chromosome (1 each side) | 2 per bivalent | 2 per chromosome |
| Chromosome number | Diploid (2n) | Diploid (2n) | Haploid (n) |
| Outcome | Equal chromatid separation | Homolog separation | Chromatid separation |
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Related Terms
Prophase
Prophase is the first and typically longest stage of mitosis, during which chromatin condenses into distinct, visible chromosomes and the mitotic spindle begins to assemble. The nuclear envelope breaks down toward the end of prophase, and each chromosome is revealed as two sister chromatids joined at the centromere. In meiosis, prophase I is particularly significant because homologous chromosomes pair up (synapsis) and exchange genetic material through crossing over.
Anaphase
Anaphase is the stage of cell division during which sister chromatids are pulled apart by shortening spindle fibers and migrate toward opposite poles of the cell. In mitosis, cohesion proteins between sister chromatids are cleaved, allowing each chromatid (now called a chromosome) to move to a pole. Anaphase is the shortest phase of mitosis and is driven by the depolymerization of spindle microtubules and motor proteins such as dynein.
Spindle Fiber
Spindle fibers are dynamic protein structures made of microtubules that form the mitotic spindle apparatus during cell division, responsible for physically separating chromosomes to opposite poles of the cell. They originate from microtubule-organizing centers (centrosomes in animal cells) and attach to chromosomes at specialized protein complexes called kinetochores located on the centromere. Spindle fibers exert pulling forces by depolymerizing (shortening), generating the mechanical work needed to move chromosomes reliably during mitosis and meiosis.
From Greek "meta" meaning middle or between and "phasis" meaning appearance; named to reflect the middle position of chromosomes at the cell's equator during this stage.