Question

Gunter korge

Map d Gunter Korge examined several proteins that are secreted from the salivary glands of Drosophila melanogaster during larval development. One protein, called protein fraction four, was encoded by a gene found by deletion mapping to be located on the X chromosome at position 3C. (G. Korge. 1975 Proceedings of the National Academy of Sciences of the United States of America 72:45504554) Korge observed that, about five hours before the first synthesis of protein fraction four, an expanded and puffed-out region formed on the X chromosome at position 3C. This chromosome puff disappeared before the end of the third larval instar stage, when the synthesis of protein fraction four ceased. He observed that there was no puff at position 3C in a special strain of flies that lacked secretion of protein fraction four What is the chromosome puff at position 3C? O a region of positive supercoiling O O O a region of DNA replication a region of active transcription a region of heterochromatin Why does the disappearance of the puff at position 3C roughly coincide with lack of the secretion of protein fraction 4? The disappearance of the puff at region 3C indicates decreased protein expression from the entire chromosome The disappearance of the puff at region 3C indicates fewer copies and limited expression of the genes encoding protein fraction 4. The disapperance of the puff at region 3C indicates a lack of transcription from the region with gene for protein fraction 4

Answer 1

A chromosome puff is the site or location of intense transcriptional activity on a chromosome. If any particular protein has to be expressed on a large scale, then the gene that encodes that particular protein will be transcribed more.

During this intense transcriptional activity, the site of that gene which encodes this protein, will appear like a puff on the chromosome.

Hence answer for first question is "the region of active transcription".

Soon after the function of that protein is over, there is no need of that protein to be secreted.

Then, the transcription of its encoding gene will be stopped. Thus, that chromosome puff will disappear. So secretion of protein will be stopped.

The answer for second question is "the disappearance of the puff at region 3C indicates a lack of transcription from the region with gene for protein fraction 4".