Division of Cells

The Division of cells 1. What is specifically accomplished in mitosis? In meiosis? a. Mitosis is when a single nucleus becomes two nuclie that are genetically identical to each other and to the parent nucleus. It begins with a phase know as prophase. In this phase, the nucleolar material seperates. The centrosomes move away from each othe and twards opposite ends of the cell. These centrosomes organise microtubules and serve as their mitotic center. Polar microtubules run between the mitotic centers and make up the devloping spindle. The spindle is actually made up of two half spindles. The polar microtubule runs from one mitotic center to the middle of the spindle. Here it overlaps with polar microtubules of the othe half spindle. These polar microtubules are constantly forming and falling apart. The only time they become stable is when they contact the polar microtubules from other half spindle. The cromatin also changes during prophase. The extremely long, thin fibers coil, twist and compact making them appear more orderly. Within in the tight binding of the chromatids lies the centromere, this must be present in order for the chromatids to become associated with the microtubules. een interpase and prophase the cromatin begin to coil together. The next phase is prophase. The intermediate phase is called Prometaphase. In prometaphase, teh nuclear envelope breaks down. The kinetichore microtubules appear and interact with the olar microtubules of the spindle. This resultes in movement of the chromosomes. The nexxt phase is metaphase. In metaphase the duplicated centromere regions connect paired chromatids become aligned in a plane at the cell's equator. In anaphase, each centromere divides and the new chromosomes begin to move tward the poles. The telophase consists of the seperating of the chromosomes reaching the poles. Telophase passes into the next interphase as the nuclear envelopes and nucleoli re-form and the chromatin becomes diffuse. Interphase is when the nucleus replicates its DNA and centrosomes. b. In meoisis I prophase once again starts the cicle. In prophase the chromatin begin to condense following interphase, and the snapsis aligns homologs. Chromosomes also shorten. The chiasmata thenbecomes evident. The coiling and shortening of the chromosomes continue. Then in metophase the chromosomes line up on the equatoial. Anaphase then starts. The homologous chtomosomes move to opposite poles of the cell. In telophase the chromosomes gather into nuclei and the origonal cell divides. Then meosis II starts. In prophase the chromosomes condence again following a brief interphase in which DNA does not replicate. Metaphase constists of the kinetochores of the paired chromatids line up across the equator of each cell. In anaphase, the chromatids of the chromosomes finally seperate becoming chromosemes in their own right. They are then pulled to opposite poles. In telophase the chromosomes gather into nucleu and the cells divide.each of the four cells has a nucleus with a haploid number of chromosomes. 2. How does the first meiotic division differ from the second meiotic division? In the first meiotic division the DNA replicates forming two identical pairs ready for seperation. In the second, the DNA is not replicated. This couses the final four cells that form to only have a haploid number of chromosomes. 3. Which organs in both higher plants (gymnosperms and angiosperms) and animals are associated with meiosis? The places meiosis take place in the higher plants in the emryo sacs and in the pallen grains. In animals it takes place in the ovaries and the testes. 4. What would happen if a cell underwent mitosis but not cytokineses? Give an example of on organism that does not follow mitosis with cytokinesis. If a cell under went mitosis but not cykinesis, there would be two nucleuses in one cell. An organism that does not follow mitosis with cytokinesis is bacteria. The reason for this is that bacteria do not have nucleuses, so therfore they do not perform mitosis. Since mitosis is not performed and cytokineses still is cytoinesis can not folow mitosis.