Question:

Polytene chromosomes are formed due to

Updated On: Jun 21, 2022
  • mitosis
  • meiosis
  • endomitosis
  • endomixis.
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The Correct Option is C

Solution and Explanation

Polytene chromosomes, first reported by Balbiani .in 1881 in salivary glands of Chironomus and other insects, are popularly called salivary chromosomes. They can reach a length of 2000 ?m and may contain 1000- 16000 times DNA, as compared to ordinary somatic -chrornosomes.: They. are formed by. somatic pairing, between homologous chromosomes, ~ and repeated replication or endomitosis of their chromonemata. They bear conspicuous swellings called chromosome puffs, larger swellings are called Balbiani rings. In the puff region, DNA strands uncoil, become active and produce mRNA. For synthesis of mRNA; the puffs are concentrated with RNA polymerases.
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Concepts Used:

Cell Cycle and Cell Division

Cell Cycle:

The sequence of events by which a cell copies itself synthesizes other constituents of the cell and eventually splits into two daughter cells is termed the cell cycle. The cell synthesizes all its constituents in a sequential pattern to make sure the proper division and distribution of components that occurs between the two daughter cells. Therefore, we can say that the cell cycle is the period of time between the development of new daughter cells and their further division.

Stages of Cell Cycle:

The cell cycle can be sub-divided into an additional category of Interphase. Meanwhile, the Interphase can be branched into 3 further stages, such as:

  1. G1 Phase - “Gap 1 Phase”
  2. S Phase - "Synthesis Phase"
  3. G2 Phase - "Gap 2 Phase"

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Cell Division:

The division of the parent cells into two or more cells is called daughter cell, cell division takes place. In general, it occurs as a part of a larger cell cycle. All the cell reproduces by dividing into two, wherein each parental cell produces two daughter cells.

Stages of Cell Division:

Cell division can be widely divided into several sub-segments that result from Mitosis and Meiosis.

  1. Mitosis or (M Phase)
  2. Meiosis