Question

Polytene chromosome was first observed by
A. Setevens and Wilson
B. Heitz and Bauer
C. Balbiani
D. Khorana

Answer 1

Polytene chromosomes are large chromosomes having thousand of DNA strands. They are present in the salivary glands of insects, so this chromosome is widely known as the salivary glands chromosome. They are found in dipteran flies such as Drosophila. They are produced when repeated rounds of DNA replication without cell division which form a giant chromosome. Polytene chromosomes are having distinct patterns of thick and thin bands. These chromosomes are now used to study the function of genes in transcription.

Complete Answer:
- The polytene chromosome was observed in the salivary glands of the larva of Chironomus midges (non biting insects) by Balbiani in 1881.
- He described the chromosomal puffs among the tangled thread inside the nucleus and had given the name of “permanent spireme”. This was later observed in the salivary glands of Drosophila melanogaster or fruitfly by Emil Heitz and Hans Bauer But in the 1930s that helped to study the hereditary nature of these structures.
- They are formed from the chromosome of diploid nuclei by the successive duplication of each chromosomal element (chromatid) without their segregation. Newly formed chromatids remain associated lengthwise and together form a cable-like structure i.e. polytene chromosome.

Hence the correct answer is Balbiani.

Note: This chromosome was first seen by Balbiani in the salivary glands of the larva of non-biting insects (Chironomus midges). These chromosomes are found during the cell division in the nuclei of the cells of the salivary glands of the larvae of Diptera (fruit fly or Drosophila melanogaster).