Why are polytene chromosomes in fly larvae?

Polytene chromosomes were first reported by E.G.Balbiani in 1881. Polytene chromosomes are found in dipteran flies: the best understood are those of Drosophila, Chironomus and Rhynchosciara. Thus polytene chromosomes form when multiple rounds of replication produce many sister chromatids which stay fused together.

Where are polytene chromosomes found?

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.

What is a polytene chromosome?

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.

Which organ is generally used to find the polytene chromosome in Drosophila?

Polytene chromosomes form in the Drosophila giant salivary gland during development by multiple rounds of genome replication without cell division to generate polytene chromosomes containing up to 1000 copies of DNA per chromosome.

What are Balbiani rings?

Balbiani rings are exceptionally large puffs on the polytene chromosomes in the dipteran Chironomus tentans. These puffs are particularly well suited for studies of the structure of active genes and the synthesis and transport of specific RNA-protein (RNP) particles.

What is the difference between Lampbrush chromosome and polytene chromosome?

The main difference between polytene and lampbrush chromosome is that polytene chromosomes occur in the salivary glands and other tissues of insects whereas lampbrush chromosomes occur in the oocytes of vertebrates except for mammals and some invertebrates.

What is the function of Lampbrush chromosome?

Lampbrush chromosomes are also involved in the production of “masked” mRNAs for early development. The giant granular loops could either be the sites where such mRNAs are packaged or they could be sites where specific alterations of the deoxyribonucleoprotein fiber take place.

What is the significance of Lampbrush chromosome?

Giant chromosomes in the lampbrush form are useful model for studying chromosome organization, genome function and gene expression during meiotic prophase, since they allow the individual transcription units to be visualized.

Which is largest chromosome Polytene or Lampbrush?

[II] Polytene chromosomes: These are also giant chromosomes but relatively smaller than lampbrush chromosomes, found in the larvae of certain dipterans. Because of their large size showing numerous strands these are named as polytene chromosomes (name suggested by Kollar) or commonly salivary gland chromosomes.

What are the 2 main types of chromosomes?

Chromosomes in humans can be divided into two types: autosomes (body chromosome(s)) and allosome (sex chromosome(s)). Certain genetic traits are linked to a person’s sex and are passed on through the sex chromosomes. The autosomes contain the rest of the genetic hereditary information.

What are the two basic types of chromosomes?

Among many organisms that have separate sexes, there are two basic types of chromosomes: sex chromosomes and autosomes. Autosomes control the inheritance of all the characteristics except the sex-linked ones, which are controlled by the sex chromosomes. Humans have 22 pairs of autosomes and one pair of sex chromosomes.

Where are polytene chromosomes found in a larva?

Polytene or Giant chromosomes are over-sized chromosomes commonly found in the salivary glands of larval stages of Drosophila and Chironomus dipteran flies. In those, glandular cells undergo endomitosis without cell division.

Where was polytene chromosome found in chironomous midges?

Balbiani in 1881, first found polytene chromosome in the larval salivary glands of Chironomus midges but the hereditary nature was confirmed by Emil Heitz and Hans Bauer in 1930 in Drosophila melanogaster.

Why are polytene chromosomes found in the salivary glands?

In insects, polytene chromosomes are commonly found in the salivary glands; they are also referred to as “salivary gland chromosomes”. The large size of the chromosome is due to the presence of many longitudinal strands called chromonemata; hence the name polytene (many stranded).

What are the banding patterns on a polytene chromosome?

Polytene chromosomes, at interphase, are seen to have distinct thick and thin banding patterns. These patterns 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.