Understanding Key Biological Discoveries and Scientists

This question asks us to match significant discoveries and concepts in the field of biology, particularly genetics and molecular biology, with the scientists who are credited with them. To answer this, we need to recall the key contributions of each scientist listed.

Matching List I (Discoveries/Concepts) with List II (Scientists)

Let's analyze each item in List I and find its corresponding match in List II:

• (A) Transforming principle: This concept came from experiments by Frederick Griffith in 1928. He showed that something from heat-killed smooth bacteria could transform rough bacteria into smooth bacteria. This 'something' was later identified as DNA. Therefore, (A) matches with (II) Frederick Griffith.
• (B) Replication of DNA: While the exact mechanism of semi-conservative replication was proven by Meselson and Stahl, the double helix structure of DNA proposed by James Watson and Francis Crick (with contributions from Rosalind Franklin and Maurice Wilkins) in 1953 provided the crucial insight into how DNA could replicate. Their model immediately suggested a mechanism for replication. Therefore, (B) matches with (IV) Watson and Crick.
• (C) Lac operon concept: The operon model, which explains gene regulation in bacteria (specifically the regulation of genes involved in lactose metabolism), was proposed by François Jacob and Jacques Monod in 1961. Therefore, (C) matches with (I) Jacob and Monod.
• (D) DNA Fingerprinting: This revolutionary technique, used for identification based on variations in DNA sequences, was developed by Alec Jeffreys in 1984. Therefore, (D) matches with (III) Alec Jeffreys.

Summary of Matches

Based on the analysis, the correct matches are:

• (A) Transforming principle → (II) Frederick Griffith
• (B) Replication of DNA → (IV) Watson and Crick
• (C) Lac operon concept → (I) Jacob and Monod
• (D) DNA Fingerprinting → (III) Alec Jeffreys

This gives us the sequence A-II, B-IV, C-I, D-III.

Revision Table: Key Biology Discoveries and Scientists

Additional Information on Genetics and Molecular Biology

The topics covered in this question are fundamental to genetics and molecular biology. Let's delve a little deeper into some related concepts:

The Transforming Principle Explained Further

Frederick Griffith's experiment involved injecting mice with different strains of *Streptococcus pneumoniae*. The 'S' strain (smooth) was virulent, while the 'R' strain (rough) was non-virulent. Heat-killed S strain was also non-virulent. However, when a mixture of heat-killed S strain and live R strain was injected, the mice died, and live S strain bacteria were recovered. This showed that some substance from the heat-killed S strain had 'transformed' the live R strain into the virulent S strain. Oswald Avery, Colin MacLeod, and Maclyn McCarty later identified DNA as this transforming principle in 1944.

DNA Replication Details

The Watson and Crick model of the DNA double helix suggested that each strand could serve as a template for synthesizing a new complementary strand. This semi-conservative model was experimentally proven by Meselson and Stahl in 1958 using isotopes of nitrogen. DNA replication is a complex process involving many enzymes like DNA polymerase, helicase, ligase, etc.

Understanding Operons

An operon is a functional unit of DNA that contains a cluster of genes under the control of a single promoter. It includes structural genes (coding for proteins), a promoter (where RNA polymerase binds), an operator (a regulatory region), and sometimes a regulator gene (coding for a repressor or activator protein). The lac operon is an inducible operon, meaning it is typically off but can be turned on in the presence of lactose. This is a key example of how gene expression is regulated in prokaryotes.

Applications of DNA Fingerprinting

DNA fingerprinting (also known as DNA profiling) exploits variations in repetitive DNA sequences, such as Variable Number Tandem Repeats (VNTRs) or Short Tandem Repeats (STRs), between individuals. Since these patterns are highly variable, they can be used for identification. Applications include forensic science (identifying suspects or victims), paternity testing, identifying remains, and studying genetic diversity.