1. Estimate the length of a representative chromosome assuming that it could be

Question

1. Estimate the length of a representative chromosome assuming that it could be linearized. Keep in mind that your photo most illustrates a mass of chromosomes attached at the chromocenter as illustrated in figure 1.

Insert your microscope photo and calculations and explain your reasoning.

2.

Estimate the relative expansion of your prepared polytene chromosomes by comparing its packing ratio to a reference of 2x104 base pairs/nm for an interphase human chromosome (this reference was calculated based on data obtained from Am J Hum Genet, 2002). To estimate this ratio, you will first need to establish the average chromosome length (# DNA base pairs) in Drosophila virilis. This can be done by referring to the 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?

Insert your full calculation details and reasoning.

Explanation / Answer

You have not provided the scale with the diagram which makes it difficult to answer.

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