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Chapter 5
Principles of Inheritance
and Variation

Chapter 6
Molecular Basis of Inheritance

Chapter 7
Evolution

The work of Mendel and others who followed him gave us an
idea of inheritance patterns. However the nature of those ‘factors’
which determine the phenotype was not very clear. As these
‘factors’ represent the genetic basis of inheritance, understanding
the structure of genetic material and the structural basis of
genotype and phenotype conversion became the focus of
attention in biology for the next century. The entire body of
molecular biology was a consequent development with major
contributions from Watson, Crick, Nirenberg, Khorana, Kornbergs
(father and son), Benzer, Monod, Brenner, etc. A parallel problem
being tackled was the mechanism of evolution. Awareness in the
areas of molecular genetics, structural biology and bio informatics
have enriched our understanding of the molecular basis of
evolution. In this unit the structure and function of DNA and the
story and theory of evolution have been examined and explained.

James Dewey Watson was born in Chicago on 6 April 1928. In 1947, he
received B.Sc. degree in Zoology. During these years his interest in
bird-watching had matured into a serious desire to learn genetics. This
became possible when he received a Fellowship for graduate study in
Zoology at Indiana University, Bloomington, where he received his Ph.D.
degree in 1950 on a study of the effect of hard X-rays on bacteriophage
multiplication.
He met Crick and discovered their common interest in solving the
DNA structure. Their first serious effort, was unsatisfactory. Their second effort
based upon more experimental evidence and better appreciation of
the nucleic acid literature, resulted, early in March 1953, in the proposal
of the complementary double-helical configuration.
Francis Harry Compton Crick was born on 8 June 1916, at Northampton,
England. He studied physics at University College, London and obtained
a B.Sc. in 1937. He completed Ph.D. in 1954 on a thesis entitled “X-ray
Diffraction: Polypeptides and Proteins”.
A critical influence in Crick’s career was his friendship with J. D.
Watson, then a young man of 23, leading in 1953 to the proposal of
the double-helical structure for DNA and the replication scheme. Crick
was made an F.R.S. in 1959.
The honours to Watson with Crick include: the John Collins Warren
Prize of the Massachusetts General Hospital, in 1959; the Lasker Award,
in 1960; the Research Corporation Prize, in 1962 and above all, the
Nobel Prize in 1962.