Phases of the cell cycle (article) | Khan Academy
Prophase | Metaphase | Anaphase | Telophase | Cytokinesis | Links They acquire ATP and increase in size during the G1 phase of Interphase. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates. The process begins with interphase and ends with cytokinesis. Mitosis is the phase of the cell cycle where chromosomes in the nucleus are evenly divided between two cells. . In meiosis, four daughter cells are produced. Cytokinesis then occurs, dividing the cytoplasm and cell body into two new cells. Mitosis is divided into four major stages that take place after interphase (Figure.
Homologous chromosomes pair up and exchange fragments in the process of crossing over. Homologue pairs line up at the metaphase plate. Homologues separate to opposite ends of the cell.
Sister chromatids stay together. Each chromosome still has two sister chromatids, but the chromatids of each chromosome are no longer identical to each other.Phases of Mitosis
When the homologous pairs line up at the metaphase plate, the orientation of each pair is random. For instance, in the diagram above, the pink version of the big chromosome and the purple version of the little chromosome happen to be positioned towards the same pole and go into the same cell. But the orientation could have equally well been flipped, so that both purple chromosomes went into the cell together.
This allows for the formation of gametes with different sets of homologues. Can you show me what you mean?
Meiosis | Cell division | Biology (article) | Khan Academy
Here is a diagram that illustrates the point a little more clearly: Diagram showing the relationship between chromosome configuration at meiosis I and homologue segregation to gametes. In this case, four different types of gametes may be produced, depending on whether the maternal homologues are positioned on the same side or on opposite sides of the metaphase plate.
In anaphase I, the homologues are pulled apart and move apart to opposite ends of the cell. The sister chromatids of each chromosome, however, remain attached to one another and don't come apart. Finally, in telophase I, the chromosomes arrive at opposite poles of the cell.
Cytokinesis usually occurs at the same time as telophase I, forming two haploid daughter cells. These cells are haploid—have just one chromosome from each homologue pair—but their chromosomes still consist of two sister chromatids.
The Cell Cycle, Mitosis and Meiosis
In meiosis II, the sister chromatids separate, making haploid cells with non-duplicated chromosomes. Starting cells are the haploid cells made in meiosis I.
Chromosomes line up at the metaphase plate. Sister chromatids separate to opposite ends of the cell. Newly forming gametes are haploid, and each chromosome now has just one chromatid.
During prophase II, chromosomes condense and the nuclear envelope breaks down, if needed. Endoreduplication or endoreplication occurs when chromosomes duplicate but the cell does not subsequently divide. This results in polyploid cells or, if the chromosomes duplicates repeatedly, polytene chromosomes.
Instead of being divided into two new daughter nuclei, the replicated chromosomes are retained within the original nucleus. Platelet -producing megakaryocytes go through endomitosis during cell differentiation.
Karyokinesis without cytokinesis originates multinucleated cells called coenocytes. Related cell processes[ edit ] Cell rounding[ edit ] Cell shape changes through mitosis for a typical animal cell cultured on a flat surface. The cell undergoes mitotic cell rounding during spindle assembly and then divides via cytokinesis. Rounding also occurs in live tissue, as described in the text.
Mitotic cell rounding In animal tissue, most cells round up to a near-spherical shape during mitosis.
Generation of pressure is dependent on formin -mediated F-actin nucleation  and Rho kinase ROCK -mediated myosin II contraction,    both of which are governed upstream by signaling pathways RhoA and ECT2   through the activity of Cdk1. Mitotic recombination[ edit ] Mitotic cells irradiated with X-rays in the G1 phase of the cell cycle repair recombinogenic DNA damages primarily by recombination between homologous chromosomes.
Phases of the cell cycle
Evolution[ edit ] Some types of cell division in prokaryotes and eukaryotes There are prokaryotic homologs of all the key molecules of eukaryotic mitosis e.
Being a universal eukaryotic property, mitosis probably arose at the base of the eukaryotic tree. As mitosis is less complex than meiosismeiosis presumably arose after mitosis. In relation to the forms of mitosis, closed intranuclear pleuromitosis seems to be the most primitive type, as it is the more similar to bacterial division.
Polar microtubules, shown as green strands, have established a matrix around the currently intact nucleus, with the condensing chromosomes in blue.