What is the structure of a polytene chromosome?
The polytene chromosome contains two types of bands, dark bands and interbands. 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.
What is polytene chromosome explain in detail?
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.
Where is polytene chromosome 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.
Why polytene chromosomes are formed?
As they were discovered in the salivary glands so they are also known as salivary gland chromosomes. They are termed as polytene due to the presence of many chromonemata. They are formed due to repeated duplication of chromosomes without separation. It is known as endomitosis.
Who discovered polytene chromosome?
Balbiani
Polytene chromosomes were first discovered in the 1880s in insects (Balbiani 1881). One of the earliest published examples of polytene chromosomes is of Chironimus salivary gland chromosomes found in Walther Flemming’s 1882 book, Zellsubstanz, Kern, und Zelltheilung (Flemming 1882).
How many arms are in a polytene chromosome?
It is a giant chromosome with 5 long and 2 short arm radiating from a central point called chromocentre. It is 2000 μm in length (7.5 μm in somatic cells).
How many chromosomes are present in a polytene chromosome?
four chromosomes
Polytene homologues are held together by somatic pairing. The centromeres of all four chromosomes aggregate to form a chromocentre that is seen amorphous and consists largely of heterochromatin.
Are polytene chromosomes haploid or diploid?
The end product of the replication cycles is a nucleus with a haploid number of chromosomes, each containing up to 2,000 or more parallel strands. In the Collembola, however, the polytene chromosomes typically remain unpaired and the nuclei contain the diploid number (Fig. 92).