Research Paper On Meiosis

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INTRODUCTION : Meiosis is the second important kind of nuclear division. It resembles mitosis in many ways but the consequences of meiotic divisions are very different from those of mitotic divisions. While mitotic division may occur in almost any living cell of an organism, meiosis occurs only in special cells. In animals, meiosis is restricted to cells that form gametes (eggs and sperm). Each species has a characteristic number of chromosomes per somatic cell. Fruit flies have 8; normal humans have 46. They exist as homologous pairs (partners) that are similar in size and shape and carry the same kinds of genes. Thus humans have 23 homologous pairs. The full complement of 46 chromosomes is referred to as the diploid number (referring to the fact that each kind of chromosome is represented twice). In higher organisms when an egg is fertilized the egg and sperm fuse to form a single cell called a zygote which develops into a new organism. If the egg and sperm were both diploid (46 chromosomes each in the case of humans) then the resulting zygote would be tetraploid. This would be an intolerable situation, so a mechanism has evolved to insure that each gamete (egg or sperm) contains only one representative of each homologous pair (or half the diploid number). This is referred to as the haploid number. In this experiment, the meiotic process is occurs in angiosperm. Pollen mother located in anthers undergo meiosis and form microspores. The haploid nucleus of each microspore subsequently divides mitotically to give rise to a three nucleate male gametophyte. Pollen grains in the anthers are transferred to the stigma of the pistil by insects or wind. There they germinate and begin to grow a pollen tube, which passes down the style and into the ovary of the pistil. The pollen tube carries the sperm nuclei to the ovule. The pollen tube enter the ovule through the ovule through a pore in the integuments called the micropyle; once inside the ovule, the pollen tube burst and frees the sperms nuclei inside the female gametophytes. The pollen tube nucleus then disintegrate. Double fertilization occurs in angiosperms. One of the sperm nuclei carried into the gametophyte unites with the egg to form diploid zygote subsequently divide mitotically to give rise embryo. The second sperm nucleus unites with the two polar nuclei of the female gametophytes.

LEARNING OUTCOMES: 1. Prepare an aceto-orcein squash of anthers from a flower buds. 2. Demonstrate the stage of meiosis in microsporogenesis. 3. Identify the basic features of meiosis

MATERIALS 1. 70% ethyl alcohol 2. Absolute ethyl alcohol 3. Acetocarmine stain in dropping bottle 4. Bunsen burner 5. Cover slip 6. Teasing needles 7. Forceps 8. Compound Microscope 9. Scalpel or razor blade 10. Slides 11. Supply of immature flower buds (chives) 12. Watch glass

METHODS 1. An individual flower bud was remove from the storage container and was placed in a watch glass. A few drops of 70% ethyl alcohols were added to keep the anther moist. 2. Individual flower buds moist in alcohol were continually kept to dissect the anthers from the bud. 3. Some anther was transfer to a clean microscope slide and was placed in a drop of aceto-orcein stain. A teasing needle was use to macerates the anthers, freeing the microsporocytes from the anther walls. 4. A cover slip was applied and was heat over the Bunsen burner. Stain was added to prevent dying. 5. Paper toweling was use to cover the slide after heating and was press down firmly with thumb. This will flatten the microsporocytes and make it possible to observe the chromosome in the various meiotic stages. 6. If anther from more than one flower is crushed, different stages are likely to be observed. The slide was observed by using the compound microscope.

QUESTION AND ANSWER 1. Does crossing over occur before or after chromosome duplication in cells going through meiosis?
Crossing over occurs
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