Mitosis and Meiosis
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There are two types of nuclear division, mitosis and meiosis. Mitosis is usually used for the growth and replacement of somotaic cells, while meiosis produces the gametes or spores used in an organism’s reproduction.
Mitosis occurs in whitefish blastula and onion root tip, and it is easily observable. Meiosis and crossing over occurs in the production of gametes and spores.
This lab required prepared slides of whitefish blastula, onion root tips, ovary, and testis, a microscope, and chromosome kit. The prepared slides of whitefish blastula and onion root tips, ovary, and testis were observed under the 10x and 40x objectives.
Mitosis is easily observed in cells that are growing at a rapid pace such as whitefish blastula or onion root tips, which was used in this lab experiment. The root tips contain and area called the apical meristem that has the highest percentage of cells undergoing mitosis. The whitefish blastula is formed directly after the egg is fertilized. This is a period of rapid growth and numerous cellular divisions where mitosis can be observed. In mitosis the cell is in interphase, and have a distinct nucleus and nucleoli where the thin threads of chromatin thicken into distinct chromosomes and the nuclear evvelope breaks open releasing them into the cytoplasm. The firs signs of the spindle begin to appear, next the cell begins metaphase, where the spindle attaches to the Centromere of each chromosome and moves them to the same level in the middle of the cell. This level position is called the metaphase plate. Anaphase begins when the chromatids are separated and pulled to opposite poles, then the final stage is telophase. The nuclear envelope is reformed and the chromosomes gradually uncoil. Cytokinesis may occur, in which, a cleavage furrow will form and the two daughter cells will separate.
Meiosis is more complex and involves two nuclear divisions. The two divisions are called Meiosis I and Meiosis II and they result in the production of four haploid gametes. This process allows increased genetic variation due to crossing over where genes can be exchanged. This process allows increased genetic variation due to crossing over where genes can be exchanged. The process , like mitosis, depends on interphase to replicate the DNA. Meiosis begins with Prophase I. In this stage, homologous chromosomes move together to form a tetrad and and synapsis begins. This is where crossing over occurs resulting in the recombination of genes. Metaphase I moves the tetrads to the metaphase plate in the middle of the cell, and Anaphase I reduces the tetrads to their original two stranded form and moves them to opposite poles. Telophase I then prepares the cell for its econd division. Meiosis II generally resembles mitosis except that the daughter cells are haploid instead of diploid. DNA replication does not occur in Interphase II, and prophase, metaphase, anaphase, and telophase occur as usual. The only change is the number of chromosomes.
LabPaq, Englewood Co, 2008
Raven, Johnson, Mason, Losos, and Singer. Biology 10th Ed., McGraw-Hill., New York, NY., 2014 http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/bio%