Introduction to Mitosis Biology 12 S.Dosman Fertilization • The union of male and female sex cells. Asexual Reproduction • The production of offspring from a single parent; offspring inherit the genes of that parent only. Sexual Reproduction • The production of offspring from the union of two sex cells, one from each different parent. The genetic makeup of the offspring is different from that of either parent. Mitosis • A type of cell division in which a daughter cell receives the same number of chromosomes as the parent cell. Cytokinesis • The division of the cytoplasm. Interphase • The time interval between nuclear divisions. During this phase, a cell increases in mass, roughly doubles the cytoplasmic components, and duplicates its chromosomes. Chromatin • The tangled fibrous complex of DNA and protein within a eukaryotic nucleus. Centromere • The structure that holds chromatids together. Sister Chromatids • A chromosome and its duplicate, attached to one another by a centromere. The pair remains attached until separated during mitosis. Centrioles • Small protein bodies that are found in the cytoplasm of animal cells. Spindle Fibres • Protein structures that guide chromosomes during cell division. Spermatocytes • Sperm producing sex cells in males; these cells can divide continuously. Blastula • An embryonic stage consisting of a ball of cells produced by cell division following the fertilization of an egg. Genetic engineering • Intentional production of new genetic material by substituting or altering existing materials. Enucleated • The condition where a cell does not contain a nucleus. Totipotent • Having the ability to support the development of an egg to an adult. Biotechnology • The use of living things in industrial or manufacturing applications. 1. List the stages of mitosis. Briefly describe that occurs in each stage. To help in your description, sketch the sequence of events that occurs in an animal cell. Include labels for different structures. • Prophase—chromosomes condense and become shorter and thicker; centrioles move to opposite poles of the cell; spindle fibers attach to the centromeres of the chromosomes; the nuclear membrane starts to dissolve. • Metaphase—chromosomes line up at the equatorial plate; the nuclear membrane completely dissolves. • Anaphase—centromeres divide and the resulting chromosomes (formerly chromatids) move to opposite poles of the cell; an identical set of chromosomes moves to each pole. • Telophase—chromosomes lengthen again; the spindle fibers dissolve; nuclear membrane forms around the chromosomes. 2. A cell with 10 chromosomes undergoes mitosis. Indicate how many chromosomes would be expected in each daughter cell. • Each of the daughter cells contains ten chromosomes. • The daughter cells should each contain the same total number as that of the parent cell. 3. During interphase, what event must occur for the cell to be capable of undergoing future divisions? • The genetic material needs to replicate. The chromosomes must once again become double-stranded. 4. Using a dictionary, look up the meaning of the prefixes used in the stages of mitosis: (pro, meta, ana, telo). Why would they be used in the naming of the phases of mitosis? • Some common answers might be the following: • “pro” — prior to • “meta” — occurring later than • “ana” — upward, backward, again • “telo” — end • Each prefix matches the events occurring during each stage of mitosis. 5. Compare and contrast the structure of the daughter cells with that of the original parent cell. • Daughter cells are genetically identical to each other and to the parent cell. • However, the daughter cells will be smaller and have fewer organelles than the parent cell. 6. Describe the structure and explain the function of the spindle fibres. • Spindle fibers are composed of microtubules. • The function of the spindle fibers is to align and direct chromosomes during cell division. 7. What is the significance of cytokinesis? Speculate what would happen if cytokinesis did not occur. • Cytokinesis produces two distinct and separate cells. It involves the division of the cytoplasm and organelles. • If cytokinesis did not occur, mitosis would result in a single cell with two nuclei. 8. When a cell has reached its maximum size, what two alternatives does it have? When does the cell carry out one alternative over the other? • When a cell reaches its maximum size, it can divide or die (death does not necessarily occur immediately; some cells specialize). • Cell division permits the survival of the organism or tissue. 9. What would happen if you ingested a drug that prevented mitosis? What if it only prevented spindle fibre formation? • Without mitosis there would be no new cells produced which means no new growth or replacement of dead cells. • No spindle fibers means that chromosomes would not be separated and there would not be an even division of the DNA. • Under both circumstances dead cells could not be replaced and the organism would die. 10. A cell from a tissue culture has 38 chromosomes. After mitosis and cytokinesis, one daughter cell has 39 chromosomes and the other has 37. What might have occurred to cause the abnormal chromosome numbers? • Both sister chromatids for one of the chromosomes moved to the same pole. • The spindle fibers failed to separate them. • Each sister chromatid duplicated its genetic information and became a separate, doublestranded chromosome. 11. Suppose that during mitosis, both sister chromatids moved to the same pole, resulting in daughter cells with a different number of chromosomes than the parent cell. How might this abnormality affect cell structure, cell function, or both? • Students may have difficulty explaining why cells with too much genetic information have difficulties. The reason will become clearer once they have examined nondisjunction; some of the duplicate information may be contradictory. • However, one cell would have too much genetic information, the other cell too little. Chemical directions carried in the chromosomes are necessary for the proper functioning of a cell, and, thus, a cell that had too little genetic information would likely not survive. • A cell with too much genetic information would also experience difficulties