Salivary Gland Chromosome Preparation

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Experiment 1
Salivary Gland Chromosome Preparation

Introduction: Microscopic, threadlike part of the cell and a structured DNA which carries hereditary information in the form of genes is a chromosome. Endomitosis is mitosis without nuclear or cellular division. This produces many copies of the same chromosome in a single nucleus (Kim 2004). For this experiment, I hypothesize that D. melanogaster undergoes endomitosis meaning without cellular mitotic division. If it undergoes endomitosis, then testable predicting result is polytene chromosomes. Material & Method: Refer it to a lab manual, Experiment 1. Salivary Gland Chromosome Preparation. I failed to obtain desirable data of chromosome out of internal larval structures of third instar D. melanogaster so I used given slide from lab co-coordinator. Results: Refer it to figure 1 and figure 2. In figure 1, salivary gland is very fragile and transparent. Discussion: As I expected, not like human chromosome, D. melanogaster undergoes endomitosis. My hypothesis was correct. In my observation, the chromosome turned out to be polytene. According to Sorsa, V. 1983, D. melanogaster’s salivary gland should have polytene chromosome. Polytene results from endomitosis, repeated replication during synapses without separation into daughter nuclei (Kim, 2004). It was very hard for me identify the chromosome, but factors of polytene chromosome was found; big, light and dark banding patterns, and all of homologous pair of chromosomes is all connected to chromocentres (Baudisch, W. 1977). When D. melanogaste chromosome and human female chromosome were compared at a stage of metaphase, human had a much smaller chromosome then fruit fly. However, human is considered “normal” then fruit fly. I believe that better microscope will definitely improve the vision of the chromosome, which will lead us better observation and results. Reference

Baudisch W (1977). "Balbiani ring pattern and biochemical activities in the salivary...
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