Write a note on the structure and significance of polytene chromosome zoology
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Polytene chromosome:
Polytene chromosomes are giant chromosomes common to many dipteran (two-winged) flies. They begin as normal chromosomes, but through repeated rounds of DNA replication without any cell division (called endoreplication), they become large, banded chromosomes (see figure). For unknown reasons, the centromeric regions of the chromosomes do not endoreplicate very well. As a result, the centromeres of all the chromosomes bundle together in a mass called the chromocenter.
Polytene chromosomes are usually found in the larvae, where it is believed these many-replicated chromosomes allow for much faster larval growth than if the cells remained diploid. Simply because each cell now has many copies of each gene, it can transcribe at a much higher rate than with only two copies in diploid cells.
The polytene chromosomes at the right are from the salivary glands of the fruit fly Drosophila melanogaster. the bands on each chromosome are like a road map, unique to each chromosome and well defined enough to allow high resolution mapping of each chromosome. The Drosophila Genome Project uses polyene chromosomes as a framework for the map.
hope it helps you!!☺
Here's your answer!!
Polytene chromosome:
Polytene chromosomes are giant chromosomes common to many dipteran (two-winged) flies. They begin as normal chromosomes, but through repeated rounds of DNA replication without any cell division (called endoreplication), they become large, banded chromosomes (see figure). For unknown reasons, the centromeric regions of the chromosomes do not endoreplicate very well. As a result, the centromeres of all the chromosomes bundle together in a mass called the chromocenter.
Polytene chromosomes are usually found in the larvae, where it is believed these many-replicated chromosomes allow for much faster larval growth than if the cells remained diploid. Simply because each cell now has many copies of each gene, it can transcribe at a much higher rate than with only two copies in diploid cells.
The polytene chromosomes at the right are from the salivary glands of the fruit fly Drosophila melanogaster. the bands on each chromosome are like a road map, unique to each chromosome and well defined enough to allow high resolution mapping of each chromosome. The Drosophila Genome Project uses polyene chromosomes as a framework for the map.
hope it helps you!!☺
Answered by
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Hey Dear,
● Polytene chromosomes -
Polytene chromosomes are large chromosomes which have thousands of DNA strands.
# Structure -
- They are found in salivary glands of insects.
- There are many longitudinal strands attributing to long size of chromosome.
- Two types of bands - dark bands & interbands.
- Presencs of puffing & Balbian rings are characteristic findings.
# Significance -
- Causes cell expansion due to increase in volume of cell nuclei.
- High level of gene expression is present.
- Endoreduplication results in production of large mucoproteins.
- Initiate replication & act as binding site for RNA.
Hope this helps you. Keep asking..
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