BIO 101 – Lab
31 October 2014
Cell Division Mitosis
Mitosis and Meiosis: Cells can be divided in unicellular organisms or in multi-cellular organisms. DNA controls the cell division. Bacteria reproduce by a process called binary fission. Bacteria have one chromosome that's attached to the cell membrane. The chromosome replicates and the two copies separate as the cell grows. Over a period of time this one cell makes two cells. Eukaryotes do the process of mitosis. In mitosis, each daughter cell gets about half of the cytoplasm from the mother cell and one copy of the DNA. Cells have to replicate the chromosomes so each daughter cell can have a set before cell division can occur. When the chromosomes have replicated and are ready to divide they consist of two identical halves called sister chromatids. A central region called the centromere joins the sister cromatids. Each individual chromosome is a long molecule of DNA and proteins. DNA makes up the genes and chromosomes that are made up of genes. Introduction
All new cells come from previously existing cells. New cells are formed by karyokinesis- the process in cell division which involves replication of the cell’s nucleus and cytokinesis-the process in cell division which involves division of the cytoplasm. Two types of nuclear division include mitosis and meiosis. Mitosis typically results in new somatic, or body, cells. Mitotic cell division is involved in the formation of an adult organism from a fertilized egg, asexual reproduction, regeneration, and maintenance or repair of body parts. Meiosis results in the formation of either gametes in animals or spores in plants. The cells formed have half the chromosome number of the parent cell. Mitosis is best observed in cells that are growing at a rapid pace, such as in the whitefish blastula or onion root cell tips. The root tips contain a special growth region called the apical meristem where the highest percentage of cells is undergoing mitosis. The whitefish blastula is formed immediately after the egg is fertilized, a period of rapid growth and numerous cell divisions where mitosis can be observed. There are several stages included in before, during, and following mitosis. Interphase occurs right before a cell enters mitosis. During interphase, the cell will have a distinct nucleus with one or more nucleoli, which is filled with a fine network of threads of chromatin. During interphase, DNA replication occurs. After duplication the cell is ready to begin mitosis. Prophase is when the chromatin thickens until condensed into distinct chromosomes. The nuclear envelope dissolves and chromosomes are in the cytoplasm. The first signs of the microtubule-containing spindle also begin to appear. Next the cell begins metaphase. During this phase, the centromere of each chromosome attaches to the spindle and are moved to the center of the cell. This level position is called the metaphase plate. The chromatids separate and pull to opposite poles during the start of anaphase. Once the two chromatids are separate, each is called a chromosome. The last stage of mitosis is telophase. At this time, a new nuclear envelope is formed and the chromosomes gradually uncoil, forming the fine chromatin network seen in interphase. Cytokinesis may occur forming a cleavage furrow that will form two daughter cells when separated. Meiosis is more complex than mitotic stages and involves two nuclear divisions called Meiosis I and Meiosis II. They result in the production of four haploid gametes and allow genetic variation because of crossing over of genetic material. Prior the process, interphase replicates the DNA. During prophase I, the first meiotic stage, homologous chromosomes move together to form a tetrad and synapsis also begins. This is where crossing over occurs, resulting in the recombination of genes. In Metaphase I, the tetrads move to the metaphase plate in the middle of the cell as...
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