What causes the swelling of the polytene chromosome?

The bands of Polytene chromosomes become enlarged at certain times to form swellings called puffs or Balbiani rings. The formation of puffs is called puffing. In the regions of puffs the chromonemata uncoil and open out from many loops. Thus puffing is caused by the uncoiling of individual chromomeres in a band.

Where can I find methods for polytene chromosome extraction?

Comprehensive methods for salivary gland and nurse cell polytene chromosome extractions, spreading and staining are also posted online at the MR4 website, in Anopheles protocols chapters 5.6 and 5.7Chapter 5.6Chapter 5.7 ( http://www.mr4.org/Portals/3/Methods_in_Anopheles_Research.pdf ).

Where are polytene chromosomes found in an insect?

Polytene chromosomes are giant chromosomes and are commonly found in the salivary glands of insects. Balbiani discovered polytene chromosomes in 1881. As they were discovered in the salivary glands so they are also known as salivary gland chromosomes.

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.

The bands of polytene chromosomes become enlarged at certain times to form swellings called puffs. The formation of puffs is called puffing. 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.

How are the inter bands of a polytene chromosome stained?

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. The interbands contain more RNA and less DNA. The amount of DNA in interbands ranges from 0.8 – 25%. The bands of polytene chromosomes become enlarged at certain times to form swellings called puffs.

Why are the puffs on a chromosome called Balbiani rings?

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. As these loops appear as rings, they are called Balbiani rings after the name of the researcher who discovered them.

Where are the polytene chromosomes found in the larvae?

When larvae develop under normal conditions, classic polytene chromosomes are seen in their salivary glands; when their food contains little protein and fat, the nuclei become reticular.