How did Meselson and Stahl experimentally prove that DNA replication is semiconservative? Explain.

5

(a)

Who proposed that DNA replication is semicoservative? How did Meselson and Stahl prove it experimentally?

5

(a)

Name the scientists who proved experimentally that DNA is the genetic material. Describe their experiment.

5

(a)

How did Hershey and Chase prove that DNA is the heredity material? Explain their experiment with suitable diagrams.

5

(a)

Answer the following questions based on Meselson and Stahl's experiment.
(a)Why did the scientists use ¹⁵NH₄Cl and ¹⁴NH₄Cl as source of nitrogen in the culture medium for growing E.Coli?
(b)Name the molecule(s) that ¹⁵N got incorporated into.
(c)How did they distinguish between ¹⁵N labelled molecules from ¹⁴N ones?
(d)Mention the significance of taking the E.coli samples at definite time intervals for observations.
(e)Write the observations made by them from the samples taken at the end of 20 minutes and 40 minutes respectively.
(f)Write the conclusion drawn by them at the end of their experiment.

5

(a)

(i) DNA polymorphism is the basis of DNA fingerprinting technique. Explain
(ii)Mention the causes of DNA polymorphism.

5

(a)

Explain the steps to DNA-fingerprinting that will help in processing of the two blood samples A and B picked up from the crime scene.

5

(a)

(a)Who proposed the concept of lac operon?
(b)Draw a labelled schematic representation of a lac operon.
(c)Explain how this operon gets switched 'on' and 'off'

5

(a)