Frequent question: Do polytene chromosomes occur due to extra rounds of DNA replication cell division or both?

How polytene chromosomes are 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 happens to the chromosome after DNA replication?

After DNA replication, each chromosome now consists of two physically attached sister chromatids. After chromosome condensation, the chromosomes condense to form compact structures (still made up of two chromatids). As a cell prepares to divide, it must make a copy of each of its chromosomes.

In which of the following ways do polytene chromosomes differ from other chromosomes?

In which of the following ways do polytene chromosomes differ from other chromosomes? Polytene chromosomes are replicated but not separated. … In the formation of nucleosomes, one histone class, H1, is not directly involved, yet it does associate with DNA to form higher level chromosomal structures.

How does a polytene chromosome differ from a typical eukaryotic chromosome?

How does a polytene chromosome differ from a typical eukaryotic chromosome? … A polytene chromosome contains banding patterns and is large because of repeated replications of DNA without nuclear division. Although mutations have been observed in many different genes, they have not been isolated in histones.

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Which chromosome is Telocentric within a polytene chromosome?

They show somatic synapsis. The centromeres of all 8 chromosomes (2n=8) are together in a structure called the chromocenter, therefore they appear to have 5 long arms and one short one (chromosome 1 is the X and is telocentric, chromosome 2 and 3 are metacentric, and chromosome 4 is tiny and is telocentric).

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.

What does polytene mean?

: relating to, being, or having chromosomes each of which consists of many strands with the corresponding chromomeres in contact.

When was the polytene chromosome first discovered and in which species?

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).