Question

Which of the following animals possess a giant chromosome?
A. Drosophila
B. Mouse
C. Pigeon
D. Elephant

Answer 1

Hint: Giant Chromosomes such as Polytene chromosomes are large chromosomes which have thousands of DNA strands. They provide a high level of function in certain tissues such as salivary glands of insects.

Complete Answer:
- Giant chromosomes are the chromosomes which has many strands of the DNA. Such chromosomes are formed due to multiple rounds of replication but without cell division. This results in formation of many sister chromatid attached to each other forming a giant chromosome. These types of chromosomes provide an ideal situation when any cell wants to produce a particular product in very excess quantity.
- Giant chromosomes are found in salivary glands of insects such as Drosophila, Chironomus larvae.
- The advantage of the giant chromosome in the salivary gland is over gene expression leading to the production of excess mucous. Such a high quantity of mucous forms adhesive glue during the pupal stage of the development.
- The polytene chromosomes appear to contain five long and one short arm radiating from a central point called chromocenter. It is formed by the fusion of centromeres of all the eight chromosomes found in the cell.
- Giant chromosomes are many times larger than the normal chromosomes reaching a length of 2000 and are visible even under a compound microscope. Polytene Chromosome was first discovered by E.G.Balbiani in 1881].

Additional Information: Apart from the Polytene chromosome there is another giant chromosome called Lamp brush chromosome. This chromosome is found in the egg of most of the mammals.

Thus the correct answer is Option A: drosophila.

Note: Apart from insect Polytene chromosome is also found in a protozoan group Ciliophora, mammalian trophoblasts cells and antipodal, and suspensor cells in plants.