polytene chromosome

Definition

Target type: cellularcomponent

A type of chromosome in a polyploid cell, formed when multiple copies of homologous chromosomes are aligned side by side to give a giant chromosome in which distinct chromosome bands are readily visible. [ISBN:0198506732]

Polytene chromosomes are giant chromosomes found in certain tissues of some insects, primarily in the salivary glands of dipteran flies. They are formed through the repeated replication of DNA without cell division, leading to a highly condensed and banded structure. The cellular component of a polytene chromosome can be described in detail as follows:

* **Chromatin:** Polytene chromosomes are primarily composed of chromatin, the complex of DNA and proteins that make up chromosomes. The chromatin is highly organized into bands, giving the chromosomes their characteristic appearance. These bands represent regions of tightly packed DNA.
* **Interbands:** The regions between the bands are called interbands. Interbands are less densely packed with DNA and represent regions of more loosely organized chromatin.
* **Chromomere:** The bands on polytene chromosomes are further subdivided into smaller units called chromomeres. Chromomeres are compact, tightly packed regions of DNA that correspond to specific genes or gene clusters.
* **Chromatin fibers:** Within the chromomeres and interbands, DNA is organized into chromatin fibers. These fibers are composed of nucleosomes, the basic units of chromatin, which consist of DNA wrapped around histone proteins.
* **Matrix:** The chromatin fibers are embedded in a protein-rich matrix that provides structural support and helps to organize the chromosome.
* **Puffs:** Polytene chromosomes can exhibit localized swellings called puffs. Puffs are regions of active gene expression, where DNA is being transcribed into RNA. These puffs are often associated with specific developmental stages or environmental stimuli.
* **Nuclear envelope:** The polytene chromosomes are enclosed within the nucleus, which is surrounded by a double membrane called the nuclear envelope. The nuclear envelope regulates the passage of molecules between the nucleus and the cytoplasm.
* **Nucleolus:** The nucleolus is a specialized region within the nucleus where ribosomes are assembled. In polytene chromosomes, the nucleolus is often associated with specific chromosomal regions that contain genes involved in ribosome biogenesis.

Overall, the cellular component of a polytene chromosome is a highly complex and organized structure that reflects the intricate interplay of DNA, proteins, and other cellular components involved in gene regulation and expression.'
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Proteins (1)

Compounds (5)