The key difference between polytene and lampbrush chromosome is that the polytene chromosome is a giant, six armed and banded chromosome present in many dipteron fly species while lampbrush chromosome is a giant chromosome present in oocytes of vertebrates that have an appearance of a lampbrush.
A chromosome refers to a thread like structure composed of tightly packaged DNA molecule and histone proteins. It also has a typical shape and an average size. However, there are extremely large sized chromosomes present in some animal cells. Structurally, they are giant chromosomes. Among these giant chromosomes, polytene and lampbrush chromosome are two examples.
CONTENTS
1. Overview and Key Difference
2. What is Polytene Chromosome
3. What is Lampbrush Chromosome
4. Similarities Between Polytene and Lampbrush Chromosome
5. Side by Side Comparison – Polytene vs Lampbrush Chromosome in Tabular Form
6. Summary
What is Polytene Chromosome?
Polytene chromosome is a giant chromosome discovered by E. G. Balbiani for the first time in 1881. Usually, they are present in dipteron fly species, especially in their salivary gland cells. Hence, initially, they were referred to as salivary gland chromosomes. According to the estimates, polytene chromosomes are many times larger and thicker than the normal chromosomes.
Figure 01: Polytene Chromosome
Unlike the normal chromosomes, they have many longitudinal strands and 1000 times more DNA. Furthermore, polytene chromosome strands have two types of bands namely dark bands and interbands. Comparatively, dark bands contain more DNA than the interbands. Hence, when we apply a nuclear stain, dark bands stain darkly in comparison to the interband as indicated above in figure 1.
What is Lampbrush Chromosome?
Lampbrush chromosome is another giant chromosome present commonly in oocytes of amphibians and in some insects. In 1882, Walther Flemming observed and recorded this giant chromosome for the first time when he analyzed the sections of salamander oocytes. Structurally this chromosome appears as a lampbrush. This appearance is due to the presence of a main chromosomal axis and throughout the axis, pairs of loops emerging in the opposite directions vertical to the main chromosomal axis. The special thing about the lampbrush chromosome is that it is not present in mammals although it is present in the growing oocytes of most animals.
Figure 02: Lampbrush Chromosome
Lampbrush chromosome is very useful as a model chromosome when studying the organization of the chromosomes, the function of the genome and expression of genes in meiotic division etc. It is due to the presence of individual transcription units in each individual loop of the lampbrush chromosome, which is easily visible. Furthermore, lampbrush chromosome is important in high-resolution mapping of DNA sequences and construction of detail cytological maps of individual chromosomes.
What are the Similarities Between Polytene and Lampbrush Chromosome?
- Both polytene and lampbrush chromosome are giant chromosomes.
- Hence, they are extremely large compared to normal chromosomes.
- Furthermore, they occur in some animal cells.
- These chromosomes can be seen under the light microscope.
What is the Difference Between Polytene and Lampbrush Chromosome?
In comparison to the normal chromosomes, some chromosomes are thicker and larger. Furthermore, they have more DNA than the normal chromosomes hence they are visible even under the light microscope. Polytene and lampbrush are two such giant chromosomes present in salivary gland cells of dipteron fly species and growing oocytes of vertebrates respectively. The key difference between polytene and lampbrush chromosome is that the polytene chromosome has many strands while the lampbrush chromosome has a lampbrush appearance. Another difference between polytene and lampbrush chromosome is that the polytene chromosome consists of two types of bands on the DNA strands while the lampbrush chromosome does not have a banding pattern. Furthermore, we can identify a difference between polytene and lampbrush chromosome based on the size too. The lampbrush chromosome is that largest chromosome recorded so far while the polytene chromosome is relatively smaller than the lampbrush chromosome.
The infographic of the difference between polytene and lampbrush chromosome below shows more details in tabular form.
Summary – Polytene vs Lampbrush Chromosome
Polytene and lampbrush chromosome are two giant chromosomes. As the name implies, they are chromosomes that are very large in size. They appear in certain stages of the life cycles of some animal cells. Accordingly, polytene chromosome is present in salivary glands of dipteron flies while lampbrush chromosome is present in growing oocytes of vertebrates. Furthermore, the polytene chromosome has many DNA strands consisting of dark bands and interbands. On the other hand, lampbrush chromosome has a main chromosomal axis and along that axis, there are vertically running pairs of loops. Thus, this summarizes the difference between polytene and lampbrush chromosome.
Reference:
1.“Kinds of Chromosomes: Lampbrush, Polytene and Supernumerary.” Biology Discussion, 27 Aug. 2015. Available here
2.“Polytene Chromosome.” Wikipedia, Wikimedia Foundation, 4 Aug. 2018. Available here
Image Courtesy:
1.”Polyten chromosome”By LPLT – Own work, (Public Domain) via Commons Wikimedia
2.”O.Hertwig1906Fig5″By Dr. Oskar Hertwig (Public Domain) via Commons Wikimedia
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