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Chromosomal puff of Polytene chromosome

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1. Explain why a well-adapted organism synthesizes only the proteins necessary at any particular moment.
2. When radioactive uracil is injected into the developing larvae of Drosophilia, only certain regions of the chromosomes in certain tissues contain radioactive uracil. Explain this observation.

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1. Protein synthesis at any particular moment depends upon the specific cellular conditions. It is a function of gene regulation or operon. Proteins in any cell are synthesized only at the time of its requirement. In ...

Solution Summary

Chromosomal puff is an important feature of salavary gland chromosome of drosophilia. Radioactive uridine is often utilized to study chromosomal puffs.

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Principles of Genetics


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Assessment 2

Part A: Questions from the Drosophila melanogaster cross practical
1) Present the results of the Drosophila cross in a suitable format. Include your results and class results. (5)
2) Explain why a reciprocal cross might be carried out in an experiment like this. (4)
3) Research the genetic basis of vestigial wings in Drosophila melanogaster. (2)
4) Carry out a Chi square test of the class results based on what you found out about the genetics. Write a null hypothesis and show all of the steps clearly. State whether you should accept or reject the null hypothesis and state your conclusion. (10)

Part B: Questions from the polytene chromosomes practical
1) From your own observations in the practical, estimate the width of a polytene chromosome on your slide. (2)
2) What are polytene chromosomes and why do they arise? (10)
3) Research other species and tissues where polytene chromosomes have been found. (10)
4) Discuss the nature of "puffs" that occur in polytene chromosomes during development. (10)

Part C: Questions from the bacterial transformation practical
1) How much DNA in ng was added to each tube of bacteria? If 250pg of DNA was required, how many l would have been needed? Show your workings clearly. (6)
2) In week 1 of the practical, plasmids were introduced into competent bacteria and plated onto selective media. Present the results of your findings in an appropriate way and state which plasmid contains which resistance gene? (10)
3) Calculate the transformation efficiency for each of the transformations you performed. Show your workings clearly. (5)

Transformation efficiency (transformants/g) = Number of colonies on plate
g of DNA per transformation

5l of plasmid at 2ng/l were used per transformation.

4) What factors may affect transformation efficiency and why? (8)
5) Present results of the gel electrophoresis including labels for each lane. (6)
6) Give an estimate for the sizes of the plasmids in base pairs. (2)

Please do not exceed the word count of 1000 words. This word count does not include titles, tables, legends, figures or references.

A further 10 marks are available for references, presentation, clarity, depth of understanding and scientific content.

This assessment is due in Thursday 5th December 5pm.

Helen McRobie 2013

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