Giant Chromosomes
Giant Chromosomes - Related Videos
10:07
Isolation of Giant Lampbrush Chromosomes from Living Oocytes of Frogs and Salamanders
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Cited by 12 •
2016
We present simple techniques for isolating giant transcriptionally active lampbrush chromosomes from living oocytes of frogs and salamanders. We describe how to observe these chromosomes "alive" by phase contrast or differential interference contrast, and how to fix them for fluorescent in situ hybridization or immunofluorescent staining.
02:04
Polytene Chromosomes
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2020
Polytene chromosomes are giant interphase chromosomes with several DNA strands placed side by side. They were discovered in the year 1881 by Balbiani in salivary glands, intestine, muscles, malpighian tubules, and hypoderm of larvae Chironomus plumosus. Hence, these are also called "Salivary gland chromosomes." These are found in insects of the order Diptera and Collembola; in certain organs of mammals; and synergids, antipodes of flowering plants. Polytene chromosomes are also regularly...
01:51
Lampbrush Chromosomes
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2020
In 1882, Flemming observed lampbrush chromosomes (LBC) in salamander eggs. Later in 1892, Rückert observed LBCs in shark egg cells and coined the term "lampbrush chromosomes" because they looked like brushes used to clean kerosene lamps. LBCs are made up of two pairs of conjugating homologous chromatids. Each chromatid consists of alternatively positioned regions of condensed-inactive chromatin and loosely placed-active side loops, which can be contracted and extended. The loops resemble the...
02:40
Chromosome Structure
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2020
A functional eukaryotic chromosome must contain three elements: a centromere, telomeres, and numerous origins of replication. The centromere is a DNA sequence that links sister chromatids. This is also where kinetochores, protein complexes to which spindle microtubules attach, are constructed after the chromosome is replicated. The kinetochores allow the spindle microtubules to move the chromosomes within the cell during cell division. Telomeres consist of non-coding repetitive nucleotide...
02:31
Chromosome Replication
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2020
Before a cell can divide, it must accurately replicate all of its chromosomes, including the DNA and its associated histone and non-histone proteins. This process begins at numerous origins of replication during the S phase of the cell cycle in each of a cell’s chromosomes simultaneously. Certain nucleotides can act as origins of replication, but these sequences are not well defined - especially in complex, multi-cellular, eukaryotic species. The length of DNA that spans an origin of...
FAQs
Polytene chromosomes arise when DNA replicates repeatedly without the cell dividing. The replicated DNA copies remain aligned, producing an extended chromosome in which structural features become large enough to observe. This mechanism links chromosome size to a specific cell-cycle history: replication continues, whereas segregation and division do not. Consequently, polytene structure provides a visible record of repeated genome duplication.
Lampbrush chromosomes emphasize a different route to visible chromosome enlargement. Extensive RNA transcription produces characteristic loops, making active transcriptional regions apparent along the chromosome. In this case, the prominent structures reflect RNA-producing activity rather than repeated DNA replication without division. The contrast helps biologists distinguish chromosome architecture associated with genome copying from architecture associated with intense gene expression.
Banding patterns provide landmarks for relating visible chromosome regions to genome organization. Replication regions indicate areas associated with DNA duplication, while transcriptional features identify regions linked to gene activity. Examining these signals together allows researchers to compare chromosome architecture with molecular processes, rather than treating chromosome appearance as a purely structural observation.
Light microscopy makes unusually extended chromosome structures accessible for direct observation. Researchers can examine banding patterns, replication regions, and transcriptional loops as visible features rather than relying only on molecular measurements. These observations provide a cytological view of how chromosome organization changes alongside DNA replication and RNA transcription, supporting comparisons between structure and activity.
Their visible transcriptional features help connect gene activity with chromosome architecture. By examining regions associated with RNA production, biologists can study how expression relates to the organization of chromatin, the chromosome material that packages genetic information. These observations also support investigations of developmental regulation, where changes in gene activity must be related to biological progression.
The enlarged, visually accessible structure makes chromosome organization available for direct comparison under light microscopy. Banding patterns and other architectural features can provide visible reference points when researchers examine changes in chromosome arrangement. This supports studies of chromosome rearrangements and helps connect large-scale structural changes with broader questions about genome organization and activity.