BIO2133-Worksheet_1 (1).docx

# Genome data viewer database of drosophila

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Genome Data Viewer database of Drosophila melanogaster to calculate the mean length of its chromosomes – one can reasonably assume that both ‘sister’ fruit fly species have chromosomes of comparable sizes. You can then estimate the ratio of DNA base pairs/nm in your preparation of polytene chromosomes by dividing the mean number of base pairs per chromosomes over the linear chromosomal length measured in the previous question. Finally compare the ratio value of your preparation of polytene chromosomes to the one of interphase human chromosomes to deduce the fold expansion of chromosomes in the salivary glands of D. virilis. Can you now explain why one can directly observe polytene chromosomes under a conventional light microscope? Chromosome X = 23 542 271 Chromosome 2L = 23 513 712 Chromosome 2R = 25 286 936 Chromosome 3L = 28 110 227 Chromosome 3R = 32 079 331 Chromosome 4 = 1 348 131

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mean = x + 2 L + 2 R + 3 L + 3 R + 4 6 mean = 133352095 6 mean = 22225349 base pairs ratio = mean / R ratio = 22225349 base pairs 35000 nm ratio = 635 base pairs nm Polytene chromosomes are more visible under a conventional compound microscope since their DNA are much larger. The average ratio of the polytene chromosomes was 635 base pairs/nm, while the average human chromosome is of length 2 000 base pairs/nm. Since the polytene chromosome has fewer chromosomes, this demonstrates that the base pairs are more spread out and are more clearly visible under a compound light microscope.
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• Winter '09
• MONTPETIT
• DNA, polytene chromosomes, Drosophilia virilius

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