Concept of gene

Presented By:
Devendra Kumar
M.Sc. (Biotechnology)
Enrolment No: B1386/14

 Gene was coined by W
Johansen in 1909
 E R Garrod (1908) proposed
One gene – one product
hypothesis
 Gene theory was proposed by
T H Morgan in 1911
 L Pauling and Ingram(1949)
established the role of genes in
protein synthesis

 G W Beadle and E L Tatum (1948)
proposed One gene – one enzyme
hypothesis
 The fine structure of gene was
proposed by Seymour Benzere(1962)
 Yanofsky (1965) proposed One gene
(cistron) – one polypeptide hypothesis
 Gene Concept was given by SUTTON

YEAR SCIENTIST GENE CONCEPT
1866 G.J. MENDEL A UNIT FACTOR THAT
CONTROLS SPECIFIC
PHENOTYPIC TRAIT
1902 SIR A.E.GARROD ONE GENE –ONE
METABOLIC BLOCK
THEORY
1940 BEADLE & TATUM ONE GENE-ONE
ENZYME THEORY
1957 U.M.INGRAM ONE GENE-ONE
POLYPEPTIDE THEORY
1960s C.YANOFSKY &
CO-WORKERS
GENE IS A UNIT OF
RECOMBINATION

 The gene is to genetics what the atom is to
chemistry.
 The gene is the unit of genetic information that
controls a specific aspect of the phenotype.
 The gene is the unit of genetic information that
specifies the synthesis of one polypeptide.

 genes are the fractions or part of DNA molecule
which regarded as the genetic material.
 T.M Morgan proposed the gene theory which
state that:
 i) Chromosomes are bearers of hereditary
units and each chromosome carries hundreds
or thousands of genes.
 ii) The genes are arranged on the
chromosomes in the linear order and on the
special regions or locus.

 Until 1940, the gene was considered as the basic unit
of genetic information as defined by following
criteria.
The unit of function, controlling the inheritance of
one “character” or phenotypic attribute.
The unit of structure, operationally defined by
recombination and by mutation.

 RECON - It is the smallest unit of
DNA capable of undergoing
Crossing Over and Recombination.
 MUTON - It is the smallest unit of DNA which
can undergo Mutation.
 CISTRON - It is the unit of Function. It is the
Gene in real sense capable of synthesizing a
Polypeptide chain of an Enzyme.
 COMPLON - It is the unit of
Complementation.

 Gene is the Unit of
Function (one gene
specifies one
character),
Recombination, and
Mutation.

 introduced by Sutton (1902) and
was elaborated by Morgan (1913).
Bidge (1923), Muller (1927) and
others which outlined as follows:
Genes are discrete particles
inherited in mendelian fashion
that occupies a definite locus in
the chromosome and responsible
for expression of specific
phenotypic character.

 Number of genes in each organism is more
than the number of chromosomes; hence
several genes are located on each chromosome.
 The genes are arranged in a single linear order
like beads on a string.
 Each gene occupies specific position called
locus.
 If the position of gene changes, character
changes.

 Genes can be transmitted from parent to off
springs.
 Genes may exist in several alternate formed
called alleles.
 Genes are capable of combined together or can be
replicated during a cell division.
 Genes may under for sudden changes in position
and composition called mutation.
 Genes are capable of self duplication producing
their own exact copies.

 Gene is the Unit of
Genetic Information,
i.e., the sequence of
DNA that specifies one
polypeptide.
 Includes coding as well
as non-coding
regulatory sequences.

 S. Benzer (1957) coined
different terms for different
nature of gene and genetic
material in relation to the
chromosome on the basis of
genetic phenomena to which
they involve.
 i) Genes as unit of transmission
or cistron
 ii) Genes as unit of
recombination or recon
 iii) Gene as unit of mutation or
muton

 The part of DNA specifying a single
polypeptide chain is termed as cistron.
 A cistron can have 100 nucleotide pairs in
length to 30,000nucleotide pairs.
 It transmits characters from one generation to
other as unit of transmission.

 The smallest segment of DNA capable of being
separated and exchange with other
chromosome is called recon.
 A recon consists of not more than two pairs of
nucleotides.

 Muton is the smallest unit of genetic material
which when changed or mutated produce a
phenotypic trait.
 muton is delimited to a singlenucleotide.

 On the basis of their behaviour
the genes may be categorized
into the following types:
 i) Basic genes: These are the
fundamental genes that bring
about expression of particular
character.
 ii) Lethal genes: These bring
about the death their possessor.

 iii) Multiple gene: When two or
more pairs of independent genes act
together to produce a single phenotypic
trait.
 iv) Cumulative gene: Some genes
have additive effects on the action of
other genes. These are called
cumulative genes.
 v) Pleiotropic genes: The genes
which produce changes in more than
one character is called pleiotropic gene.

 vi) Modifying gene: The gene which cannot
produce a character by itself but interacts with
other to produce a modified effect is called
modifier gene.
 vii) Inhibitory gene: The gene which
suppresses or inhibits the expression of another
gene is called inhibitory gene

 the influence of gene resulting in the expression
of a genetic character is called gene action.
 The genes are generally associated with the
production of enzymes, which they synthesize
from chemical substance available in the body
cells through a process of autocatalysis.

 As a rule one gene affects one enzyme. The
various actions of genes are expressed in their
development of
pigments
Colours
hormones
size and form
production of proteins
antigen and antibody
 production decisive effect on human disease
like
albinism,
 tyrosinosis etc.

 Jacob and monad
proposed “Operon
model” To explain the
mechanism of gene action
 protein synthesis is
regulated by three
specific genes located on
chromosomes
i) Structural genes
ii) Operator genes
iii)Regulator genes

Structural genes:
It regulates to produce specific mRNA
determine the kind of protein to be synthesized.
Operator genes:
These genes act as switches to turn on or turn
off the activities of structural genes
 regulating the elongation and termination of
polypeptide chain.
Regulator genes:
These genes produce certain proteinacous
substance called repressures, which prevent the
operator genes from their action.

o Determines the physical as well as
physiological characters.
o Situated in the chromosome.
o Occupies a specific position known as Locus.
o Arranged in single linear order.
o Occur in functional states called Alleles.
o Some have more than 2 alleles known as
Multiple Alleles.

o Some may undergo sudden change in
expression called as Mutant Gene (Mutation).
o May be transferred to its homologous (Cross-
over) or non-homologous counterpart
(Translocation).
o Can duplicate themselves very accurately
(Replication).
o Synthesizes a particular Protein.
o Determines the sequence of amino acid in the
polypeptide chain (The Genetic Code).

 Gupta P.K.(2009); “Genetics”; “Recombination and Resolution of
Gene”; Edition IV; Rastogi Publications; Page no:142-153
 Singh B.D.(2009); “Genetics”; “Multiple Alleles”; Edition II;
Kalyani Publishers; Page no:274-284
 Gupta P.K.(2004-05); “Fine Structure of Gene at Genetic Level”;
Edition III; Rastogi Publications; Page no:141-150
 Jain H.K.; “Gene Structure & Concept”; Edition V; Page no:192-
200
 Lewin Benjamin; “What is a Gene? A Genetic View”; Wiley
Eastern Publications; Page no:3-20
 Verma P.S. and Agarwal V.K.(2006); “Fine Structure of Gene”;
S.Chand Publication; Page no:127-133
 www.wikipedia.com
 http://www.preservearticles.com/201012251618/geneconcept.

Concept of gene

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