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Chapter 11: Problem 5

What genetic process is occurring in a puff of a polytene chromosome?

Short Answer

Expert verified
Answer: The genetic process that occurs in a puff of a polytene chromosome is gene transcription.

Step by step solution

01

Understand Polytene Chromosomes

Polytene chromosomes are large, multiple copies of DNA that are bundled together within a single chromosome. These bundles are known as chromonemata and are most commonly observed in the salivary glands of Drosophila (fruit flies) during the interphase stage of the cell cycle. Polytene chromosomes have uniquely identifiable banding patterns in which some regions are denser and others are thinner. The thin regions, called "puffs," play a crucial role in the genetic process.
02

Identify the Role of Puffs

Puffs are regions of the polytene chromosome where the chromosomal material has "puffed-up" or decondensed, allowing the DNA within them to be more accessible. Puffs are generally associated with active gene transcription, which is the genetic process by which a segment of DNA is used as a template to create a molecule of RNA that will later be translated into a protein.
03

Understanding Gene Transcription

Gene transcription is the first step in gene expression and occurs when RNA polymerase, an enzyme, binds to a specific region of the DNA, called the promoter. This promoter region signals the beginning of the gene to be transcribed. Once RNA polymerase binds to the promoter, it begins to unwind the DNA, separating the two strands, and starts to synthesize RNA using one strand of DNA as a template. As the RNA strand grows, it follows the so-called genetic code that ultimately determines which protein will be produced.
04

Identify the Genetic Process in a Puff

Since puffs are regions of the polytene chromosome where gene transcription takes place, the genetic process that occurs in a puff of a polytene chromosome is gene transcription. This process is crucial for the production of proteins, which are essential for the growth, development, and proper functioning of an organism.

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Most popular questions from this chapter

In this chapter, we focused on how DNA is organized at the chromosomal level. Along the way, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, propose answers to the following fundamental questions: (a) How do we know that viral and bacterial chromosomes most often consist of circular DNA molecules devoid of protein? (b) What is the experimental basis for concluding that puffs in polytene chromosomes and loops in lampbrush chromosomes are areas of intense transcription of RNA? (c) How did we learn that eukaryotic chromatin exists in the form of repeating nucleosomes, each consisting of about 200 base pairs and an octamer of histones? (d) How do we know that satellite DNA consists of repetitive sequences and has been derived from regions of the centromere?

Provide a comprehensive definition of heterochromatin, and list as many examples as you can.

Mammals contain a diploid genome consisting of at least \(10^{9}\) bp. If this amount of DNA is present as chromatin fibers, where each group of 200 bp of DNA is combined with nine histones into a nucleosome and each group of six nucleosomes is combined into a solenoid, achieving a final packing ratio of \(50,\) determine: (a) the total number of nucleosomes in all fibers. (b) the total number of histone molecules combined with DNA in the diploid genome. (c) the combined length of all fibers.

Contrast the structure of SINE and LINE DNA sequences. Why are LINEs referred to as retrotransposons?

The human genome contains approximately \(10^{6}\) copies of an \(A l u\) sequence, one of the best-studied classes of short interspersed elements (SINEs), per haploid genome. Individual Alus share a 282 -nucleotide consensus sequence followed by a 3 '-adeninerich tail region. Given that there are approximately \(3 \times 10^{9}\) bp per human haploid genome, about how many base pairs are spaced between each Alu sequence?
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