Mitosis Cytokinesis The stage of mitosis division
Cellular metabolic activity is high, chromosomes and organelles are duplicated, and cell size may increase. Interphase accounts for 90% of the time of each cell cycle. G1 phaseS phaseG2 phase
G1 Phase: Growth--the cell grows in size. S Phase : Prior to mitosis, the cell readies itself by duplicating its chromosomes and other cellular contents. - Before DNA synthesis, the cell’s chromosomes consist of one chromatid. - After DNA synthesis, the cell’s chromosomes consist of dyads with 2 identical sister chromatids attached at the centromere. G2 Phase : The cell prepares the enzymes and machinery for mitosis
- Chromatin Chromosome (two sister chromatids) - Nuclear envelope breaks into fragments. - Microtublues Mitotic spindle. - Some of the spindle fibers reach the chromosomes and attachit. - Nonkinetochore microtubules overlap with those coming from the opposite pole Mitosis
The chromosomes align at the equitorial plate and are held in place by microtubules attached to the mitotic spindle and to part of the centromere.
During anaphase the mitotic spindle apparatus pulls the chromatids of each chromosome apart by attaching to each centromere. Note that the telomeres of each chromosome point toward the cell’s equator.
Chromosomes begin to disperse. Spindle fibers disperse. The nuclear envelope forms again around the nuclei.
Cytokinesis begins-- formation of daughter cells. In animals, like the whitefish, a cleavage furrow, a contractile ring of muscle like fibers, pinches the cell into two.
Meiosis is a cell division process in organisms that sexually reproduce. Meiosis Sexual reproduction occurs only in eukaryotes. During the formation of gametes, the number of chromosomes is reduced by half, and returned to the full amount when the two gametes fuse during fertilization.
Human Life Cycle
Phases of Meiosis meiosis I meiosis II
Phases of Meiosis Prophase I Interphase Metaphase I Anaphase I Telophase I Meiosis I Prophase II Metaphase II Anaphase II Telophase II Meiosis II
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Crossing Over
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies