What do the puffs of polytene chromosomes represent?
In the regions of puffs, the chromonemata 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.
What is Chromocenter in polytene chromosomes?
polytene chromosome chromocentre. Definition: A region at which the centric regions of polytene chromosomes are joined together.
Where are polytene chromosomes located?
interphase nuclei
Polytene chromosomes are usually found at the interphase nuclei of some tissue of the larvae of flies. Polytene chromosomes are considered to be very useful for the analysis of many facets of eukaryotic interphase chromosome organization and the genome as a whole.
Who described polytene chromosome?
General Description of Polyteny First drawings of polytene chromosome made by Balbiani in (1881) (a) and (1890) (b). (a) Salivary gland cells of Chironomus plumosus and (b) Macronucleus (anlagen?) of Loxophyllum meleagris.
What are polytene chromosomes how are they formed?
Polytene chromosomes develop from the chromosomes of diploid nuclei by successive duplication of each chromosomal element (chromatid) without their segregation. The newly formed chromatids remain associated lengthwise and together form a cable-like structure, referred to as polytene chromosomes.
What is salivary chromosome?
Definition of salivary chromosome : one of the very large polytene chromosomal strands made up of many chromatids that are typical of the salivary gland cells of various insects.
What is the meaning of Chromomere?
Definition of chromomere : one of the small bead-shaped and heavily staining masses of coiled chromatin that are linearly arranged along the chromosome.
When are polytene chromosomes formed?
Polytene chromosomes are formed when the products of multiple rounds of S-phase remain tightly associated to form one supersized chromosome. In particular polytene chromosomes are found in a specific subset of endopolyploid cells, which have undergone a variant cell cycle known as the endocycle.
Do polytene chromosomes show somatic pairing?
In salivary gland chromosomes/polytene chromosomes, pairing is formed between homologous chromosomes. A characteristics feature of these chromosomes is that somatic pairing occurs in them and hence their number appears half of normal somatic cells.
Do humans have polytene chromosomes?
While polytene chromosomes are most frequently found in insects, they are critical in diverse organisms from ciliates to plants to humans, and they play important roles in disease progression.
What is centromere and chromomere?
The key difference between centromere and chromomere is that centromere is a constricted region that joins sister chromatids together in a chromosome while chromomere is a linearly arranged bead-like structure present along the length of the chromosome.
What is the difference between Chromonema and chromomere?
As nouns the difference between chromomere and chromonema is that chromomere is (genetics) any of a group of beadlike granules of chromatin that constitutes a chromosome during cell division while chromonema is (genetics) the coiled central filament of a chromatid upon which the chromomeres lie.
What is the band/interband pattern of polytene chromosomes?
The band/interband pattern of polytene chromosomes is constant. The interband regions that are the transcriptionally active sites on the polytene chromosomes can form an expanded state known as puffs, which are the sites where RNA is being synthesized.
Where are polytene chromosomes found?
Polytene chromosomes are a strongly amplified form of interphase chromosomes, found, for example, in salivary gland cells of Drosophila and Chironomus. From: Fluorescent and Luminescent Probes for Biological Activity (Second Edition), 1999
What do puffs and Balbiani Rings tell us about RNA synthesis?
These puffs and Balbiani rings are sites of active RNA synthesis; therefore, polytene chromosomes and more specifically puffs and Balbiani rings are excellent tools to study the induction and process of transcription.
What is the difference between chromocenter and polytene?
As the polytene chromosomes, the centromeres of all chromosomes normally aggregate to form a chromocenter that consists largely of heterochromatin. The remaining ~ 75% of the genome is organized into alternating bands and interbands in the polytene chromosome.