Direction for: In each of the following questions a statement of Assertion is given followed by a corresponding statement of Reason just below it. Of the statements mark the correct answer as
Assertion: Polytene chromosomes have a high amount of DNA. Reason: Polytene chromosomes are formed by repeated replication of chromosomal DNA without separation of chromatids.A) If both assertion and reason are true and the reason is the correct explanation of the assertion.
B) If both assertion and reason are true but the reason is not the correct explanation of the assertion.
C) If assertion is true statement but reason is false.
D) If both assertion and reason are false.
Correct Answer: A
Solution :
Balbiani first observed these chromosomes in the salivaiy glands of midge Chironomous in 1881. Thats why these are called salivary gland chromosomes. These polytene chromosomes are considered as somatic giant chromosomes and are formed by repeated replication of chromosomal DNA without separation of chromatids. After their discovery in salivary glands of larva, these chromosomes are also reported from gut epithelium, malpighian tubules and fat bodies of some other dipterans also, e.g., Drosophila, Chironomous, Sciara, Rhyncosciara, etc., These chromosomes are very long (up to 200 times their size during mitotic metaphase in Drosophila) and very thick. Thus contain a high amount of DNA.
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