Giant Chromosomes: Lampbrush and Polytene Chromosomes

 
Giant Chromosomes
Giant Chromosomes
 
The giant chromosomes are the chromosomes which
are very large in size as compared to normal
chromosomes.
They are also called as mega chromosomes.
These chromosomes are very long and thick in
appearance during metaphase than normal
chromosomes.
Hence they are called as Giant chromosomes.
The Giant chromosomes are of two types-
1. Lampbrush chromosome.
2. Polytene chromosome.
 
1. Lampbrush chromosome
1. Lampbrush chromosome
 
    Lampbrush chromosomes were first observed
by Walther Flemming in 1882 in the oocytes of
Salamander and described by Ruckert in shark oocytes in
1892.
   This is a giant chromosome which is found in the
oocytes or immature egg of most of the vertebrates such as
fishes, amphibians, reptiles and birds also in some insects.
   They are generally found in oocytes as the DNA content
is very high in these cells. They are formed in response to
the active synthesis of mRNA molecules for egg cells.
   These chromosomes are not found in mammals.
 
 
   The characteristic features of Lampbrush
chromosomes is that it include fine lateral loops that
originate from the chromomeres in the diplotene stage of
prophase first of meiosis.
    These chromosomes are found in both animal species,
vertebrates and invertebrates. So, they can be seen only
in the prophase first's diplotene stage of meiosis.
    They are generally smaller in size in case of
invertebrates than vertebrates. Its lateral loops give it its
characteristic lamp brush like appearance.
 
Structure of Lampbrush Chromosomes
Structure of Lampbrush Chromosomes
 
 
    The longitudinal axis of chromosome from which
loops are arises that are made of a single DNA molecule
each. Numerous bead-like structures called chromomeres
are arranged in a linear fashion along this axis.
   Two symmetrical lateral loops in opposite direction
emerge from each chromomere that may expand or
contract in response to different environmental
conditions.
 Biological significance
   The loops present in case of lampbrush chromosomes
are used in chromosome mapping, particularly those
loops that appear at a constant location in the
chromosome.
    It provides evidence for eukaryotic gene amplification
that is needed in the growth phase of oocytes.
    This can be used for the  analysis in hybridization
processes.
 
Polytene Chromosome
Polytene Chromosome
 
Polytene chromosomes are large chromosomes which
have thousands of DNA strands.
Polytene chromosomes were first reported
by E.G.Balbiani in 1881.
 Polytene chromosomes are found in dipteran flies, for
eg. Drosophila.
In insects, they are commonly found in the salivary
glands when the cells are not dividing.
Polytene chromosomes are produced when repeated
rounds of DNA replication without cell division forms a
giant chromosome.
Polytene chromosomes, at interphase, are seen to have
distinct thick and thin banding patterns which are called as
dark and light bands respectively.
 
Structure of Polytene Chromosome
Structure of Polytene Chromosome
 
Structure of Polytene Chromosome
Structure of Polytene Chromosome
 
In insects, polytene chromosomes are commonly found in
the salivary glands.
As their presence in salivary gland, they are also called  as
"salivary gland chromosomes".
The polytene chromosome contains two types of bands
namely-
 Dark bands and Interbands (light bands).
The dark bands are darkly stained and the inter bands are
lightly stained with nuclear stains.
The dark bands contain more DNA and less RNA and
interbands contain more RNA and less DNA. The bands of
on chromosomes become enlarged at certain times to form
swellings called puffs.
 
 
The formation of puffs in case of polytene chomosomes  is
called puffing.
In the regions of puffs, the chromonemata get uncoil and
open out to form many loops. The puffing is caused by the
uncoiling of individual chromomeres in a band.
The puffs indicate the site of active genes where mRNA
synthesis takes place. The chromonemata of puffs give out
a series of many loops laterally.
The chromonematal loops appear as rings, they are called
Balbiani rings
 
Biological significance
Biological significance
 
The banding patterns in polytene chromosomes were
originally used to help map chromosomes, identify
small chromosome mutations, and
in 
taxonomic
 identification.
They are now used to study the function of genes
in transcription.
The interbands in these chromosomes are involved in the
interaction with the active chromatin
proteins, nucleosome remodeling, and origin recognition
complexes.
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Giant chromosomes, such as lampbrush and polytene chromosomes, are significantly larger in size compared to normal chromosomes. Lampbrush chromosomes are found in oocytes of various vertebrates, while polytene chromosomes are common in dipteran flies like Drosophila. These specialized chromosomes play crucial roles in processes like gene mapping and eukaryotic gene amplification.


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  1. Giant Chromosomes The giant chromosomes are the chromosomes which are very large in size as compared to normal chromosomes. They are also called as mega chromosomes. These chromosomes are very long and thick in appearance during metaphase chromosomes. Hence they are called as Giant chromosomes. The Giant chromosomes are of two types- 1. Lampbrush chromosome. 2. Polytene chromosome. than normal

  2. 1. Lampbrush chromosome Lampbrush by Walther Flemming in 1882 in the oocytes of Salamander and described by Ruckert in shark oocytes in 1892. This is a giant chromosome which is found in the oocytes or immature egg of most of the vertebrates such as fishes, amphibians, reptiles and birds also in some insects. They are generally found in oocytes as the DNA content is very high in these cells. They are formed in response to the active synthesis of mRNA molecules for egg cells. These chromosomes are not found in mammals. chromosomes were first observed

  3. The chromosomes is that it include fine lateral loops that originate from the chromomeres in the diplotene stage of prophase first of meiosis. These chromosomes are found in both animal species, vertebrates and invertebrates. So, they can be seen only in the prophase first's diplotene stage of meiosis. They are generally smaller in size in case of invertebrates than vertebrates. Its lateral loops give it its characteristic lamp brush like appearance. characteristic features of Lampbrush

  4. Structure of Lampbrush Chromosomes

  5. The longitudinal axis of chromosome from which loops are arises that are made of a single DNA molecule each. Numerous bead-like structures called chromomeres are arranged in a linear fashion along this axis. Two symmetrical lateral loops in opposite direction emerge from each chromomere that may expand or contract in response to conditions. Biological significance The loops present in case of lampbrush chromosomes are used in chromosome mapping, particularly those loops that appear at a constant location in the chromosome. It provides evidence for eukaryotic gene amplification that is needed in the growth phase of oocytes. This can be used for the processes. different environmental analysis in hybridization

  6. Polytene Chromosome Polytene chromosomes are large chromosomes which have thousands of DNA strands. Polytene chromosomes by E.G.Balbiani in 1881. Polytene chromosomes are found in dipteran flies, for eg. Drosophila. In insects, they are commonly found in the salivary glands when the cells are not dividing. Polytene chromosomes are produced when repeated rounds of DNA replication without cell division forms a giant chromosome. Polytene chromosomes, at interphase, are seen to have distinct thick and thin banding patterns which are called as dark and light bands respectively. were first reported

  7. Structure of Polytene Chromosome

  8. Structure of Polytene Chromosome In insects, polytene chromosomes are commonly found in the salivary glands. As their presence in salivary gland, they are also called as "salivary gland chromosomes". The polytene chromosome contains two types of bands namely- Dark bands and Interbands (light bands). The dark bands are darkly stained and the inter bands are lightly stained with nuclear stains. The dark bands contain more DNA and less RNA and interbands contain more RNA and less DNA. The bands of on chromosomes become enlarged at certain times to form swellings called puffs.

  9. The formation of puffs in case of polytene chomosomes is called puffing. In the regions of puffs, the chromonemata get uncoil and open out to form many loops. The puffing is caused by the uncoiling of individual chromomeres in a band. The puffs indicate the site of active genes where mRNA synthesis takes place. The chromonemata of puffs give out a series of many loops laterally. The chromonematal loops appear as rings, they are called Balbiani rings

  10. Biological significance The banding patterns in polytene chromosomes were originally used to help map chromosomes, identify small chromosome in taxonomic identification. They are now used to study the function of genes in transcription. The interbands in these chromosomes are involved in the interaction with the proteins, nucleosome remodeling, and origin recognition complexes. mutations, and active chromatin

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