PinkMonkey Online Study Guide-Biology
CHAPTER 8:GENES AND MOLECULAR GENETICS
8.0 Introduction
Mendel (1865) was the first to put forward clearly the
idea of hereditary units, and referred to them as ’factors’. These were
later named genes. In 1903, Sutton and Bovery postulated the chromosomal
theory of inheritance and stated that the genes were located in the
chromosomes. This was subsequently confirmed by the works of Morgan and
others and is now accepted universally. Thus, it was established that
the chromosomes are the carriers of the genetic material. The chemical
of which the genes are composed is called the genetic
material.
Quest for the identification of the genetic material
The nucleic acids were discovered by Meischer in 1869. In later
years, it was also established that chromosomes are made up of proteins
(histones and protamines) and nucleic acids (DNA). Now, the question
was, which of these actually represented the genetic material? Was
it the proteins or the DNA? The process of identification of genetic
material began in 1928 and was successfully concluded in 1952. It
was conclusively established that it is the DNA that contains
the genetic material and not the proteins in the chromosomes.
This fact could be established only through some brilliantly conceived
and designed novel experiments. The most notable among these are:
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Experiments of Griffith (1928): Through his experiments, Griffith discovered the phenomenon of transformation (a special type of genetic recombination) in which the non-virulent strain of the bacterium Diplococcus pneumoniae was transformed into the virulent strain. Griffith’s experiments started the process of the identification of the genetic material.
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Avery, Macleod and Mc Carty (1944) : repeated,
elaborated and modified the transformation experiments of Griffith.
They provided the first clear evidence the DNA is the genetic material
and is responsible for the transformation in bacteria. They also gave
evidence of the chemical nature of genes.
-
Lederberg and Zinder (1952) : confirmed the
identity of DNA as the genetic material through a bacteriophage (vector),
and the subsequent incorporation of the segment in the recipient DNA
thereby causing transformation.
Hershey and Chase (1952) : confirmed that at least in the bacterial virus called T2-phage, DNA is the only genetic material. This fact has been universally accepted since then.
- Frankel - Conrai and Singer (1957) : established that in some viruses, RNA functions as the genetic material (and not the DNA).
Table 8.1: Some additional historical events
Year |
Scientists |
Discovery/Event |
1909 |
Johannsen |
Coined the term "gene"
|
1924 |
Feulgen |
Showed that chromosomes contain DNA |
1953 |
Waston and Crick |
Double stranded helical model for structure of DNA molecule |
|
Table of Contents 8.0 Introduction 8.1 Packaging of Hereditary Material 8.2
The Structure of DNA 8.3
Replication Of DNA In Eukaryotes 8.4
Replicatin of Pokaryotic Chromosome 8.5
Plasmids 8.6
RNA: Structure and Types 8.7
The Genetic Code 8.8
The Central Theme of Protein Synthesis
Chapter 9
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