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Chapter 8: Problem 28

Explain how polytene chromosomes of Drosophila are produced and how they form a six-armed structure.

Short Answer

Expert verified
Polytene chromosomes in Drosophila are a result of multiple rounds of DNA replication without cell division, leading to numerous chromatids within one cell. These chromatids align closely forming a bundle, visible as a six-armed structure under the microscope. This structure offers unique advantages in genetic studies.

Step by step solution

01

Explain the Production of Polytene Chromosomes

Polytene chromosomes are produced through a process known as endoreduplication, where the DNA is replicated without the cell dividing. This process begins when the chromosomes duplicate by replicating their DNA. However, unlike the regular cell division or mitosis, the cell does not undergo cytokinesis, therefore remaining as one cell. This replication takes place multiple times leading to numerous copies of DNA within a single cell. These multiple copies, or sister chromatids, stay closely associated forming a bundle, which is referred to as the polytene chromosome.
02

Describe the Formation of the Six-Armed Structure

The six-armed structure of the polytene chromosomes is formed through a process of chromosomal alignment. Each polytene chromosome consists of several parallel chromatids which align side by side. It is important to understand that the formation of the six-armed structure is dependent on the number of DNA replications that have occurred. In Drosophila, after 9 rounds of replication without cell division, each cell contains 512 (2^9) copies of each chromatid, making visible under the microscope the classic 'six-armed' structure of the polytene chromosomes.
03

Significance of Polytene Chromosomes

Polytene chromosomes offer a unique advantage for the study of genetics, particularly Drosophila. The precise alignment and banding patterns of the chromatids provide an excellent tool for gene mapping and studying chromosome structure and function.

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Most popular questions from this chapter

A diploid fruit fly has eight chromosomes. Which of the following terms should not be used to describe a fruit fly with four sets of chromosomes? A. Polyploid B. Aneuploid C. Euploid D. Tetraploid E. \(4 n\)

Two phenotypically normal parents produce a phenotypically abnormal child in which chromosome 5 is missing part of its long arm but has a piece of chromosome 7 attached to it. The child also has one normal copy of chromosome 5 and two normal copies of chromosome 7. With regard to chromosomes 5 and 7 , what do you think are the chromosomal compositions of the parents?

Describe some of the advantages of polyploid plants. What are the consequences of having an odd number of chromosome sets?

Which changes in chromosome structure cause a change in the total amount of genetic material, and which do not?

An inversion heterozygote has the following inverted chromosome: What would be the products if a crossover occurred between genes \(H\) and \(I\) on the inverted chromosome and a normal chromosome?
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