This presentation includes introduction of gene, gene concept, chemical composition and ultra structure of prokaryotic and eukaryotic gene for B.Sc students.

1. CONCEPT OF GENE & ULTRA
STRUCTURE OF GENE
Jigar V. Patel
Lecturer
Department of Zoology
Government Science Collage, Vankal
Ta. Mangrol, Di. Surat-394430
Email. pateljigar1818@gmail.com
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2. HISTORY
 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.
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3.  G W Beadle & 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-one polypeptide
hypothesis.
 Gene Concept was given by SUTTON.
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5. What is gene?
 A gene is the basic physical and functional unit of heredity.
It controls a character. It transmits the character from
parents to their off springs.
 A gene is a segment of DNA that specifies the sequence of
amino acids in polypeptide chain.
 Chemically Genes are made up of DNA and it is the unit of
genetic information that controls a specific aspect of the
phenotype (the set of observable characteristics of an individual
resulting from the interaction of its genotype with the environment)
by synthesizing specific polypeptide.
 Gene is present in the chromosomes of the nucleus or extra
chromosomal DNA.
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6. Location of Gene
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7.  Some genes acts as instructions to make molecules
called proteins. However, many genes do not code for
proteins.
 In humans, genes vary in size from a few hundred
DNA bases.
 The human Genome Project estimated that humans
have between 20,000 to 25,000 genes.
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8.  Every person has two copies of each gene, one
inherited from each parent.
 Most gene are same in all people, but a small number
of genes (< 1% of the total) are slightly different
between people.
 Alleles are forms of the same genes with small
differences in their sequence of DNA bases. These
small differences contribute to each person’s unique
physical features & Appearance.
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9.  Genes are the fractions or part or fragments of DNA
molecule which regarded as the genetic material.
 T.M Morgan proposed the gene theory which state
that:
1. Chromosomes are bearers of hereditary units and
each chromosome carries hundreds or thousands of
genes.
2. The genes are arranged on the chromosomes in a
linear order and on the specific region called Locus.
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10. TERMS RELATED TO GENE
• RECON- It is 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
capable of synthesizing a Polypeptide chain of an
enzyme.
• COMPLON- It is the unit of Complementation. 10

11. Classical Concept of Gene
 Introduced by sutton (1902) and was eloborate by
Morgan (1913). Bidge (1923), Muller (1927) and
others which outlined as follow:
 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. 11

12.  The genes are arranged in a single linear order like
beads on strings.
 Each gene occupies specific position called Locus.
 If the position of gene changes, character changes.
 Genes can be transmitted from parents to off springs.
 Genes may exists several alternate formed called
alleles.
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13.  Genes are capable of combined together or can be
replicated during a cell division.
 Genes may undergo sudden changes in position and
composition called Mutation.
 Genes are capable of self duplication producing their
own exact copies.
 Genes included coding as well as non-coding regions
called as axons and introns respectively.
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14. Modern concept of Gene
 Gene is a unit of genetic information or 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.
 Gene as unit of transmission or cistron.
 Gene as a unit of Recombintion or Recon.
 Gene as a unit of Mutation or Muton.
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15. Cistron- Transmission
 Benzer coined the terms cistron.
 He called cistron as a unit of Function.
 Cistron defined as a unit, alleles of which exibits cis-
trans phenomenon.
 The part of DNA specifying a single polypeptide chain
is termed as CISTRON.
 A cistron can have 100 nucleotide pairs in length to
30,000 pairs.
 It transmits characters from one generation to other
as a unit of transmission.
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16. Recon-Recombination
 The smallest segment of DNA capable of being separated
and exchange with other chromosome called Recon.
 A recon is further sub divided into units of mutation
called mutons, and several mutons in a recon will not be
separable due to recombination.
 Thus gene can consists of several cisrons, a cistron of
several recons and recons of several mutons.
 A recon and muton may be of the same size, recon may
not consists of several mutons in such cases.
 A recon consists of not more than 2 pairs of nucleotides.
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17. Muton - Mutation
 There are many position or sites within a cistron
where mutations can occur.
 Therefore, the gene as a unit of mutation is smaller.
 Muton can be defined as a unit of mutation; the
smallest unit of a gene capale of undergoing
mutation; represented by one nucleotide.
 Muton is smallest unit of genetic material which
when changed or mutated produce a phenotypic trait.
 Muton is delimited to a single nucleotide.
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27. Gene – Chemical composition
 A Gene is a segment of DNA that specifies the
sequence of amino acids in a polypeptide chain.
 Gene is present in the chromosomes of the nucleus.
 Gene is the hereditary unit. It controls a character. It
transmits the character from presents to offspring.
 Chemically gene is made up of DNA. It is located
inside the chromosomes or extra chromosomal DNA.
 The DNA is made up of two polynucleotide chains.
The two chains are helically coiled.
 Each polynucleotide chain consists of a series of units
called nucleotides.
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28. • In a DNA, there are 4 types of nucleotides, namely
1. Adenylic acid (A)
2. Guanylic acid (G)
3. Thymidylic acid (T)
4. Cytidylic acid (C)
 The four nucleotides are repeatedly arranged in a
polynucleotide chain in a linear fashion.
 The nucleotides of the two chains of a DNA are
linked by hydrogen bonds.
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29.  One chain is complementary to the other chain.
 The adenine of one chain is linked to thymine of the
second chain. Similarly, the guanine of one chain is
linked to the cytosine of the second chain. So if the
sequence of one chain is known , the sequence of the
second chain can be identified.
 One end of the polynucleotide chain is called 3prime
end (3’) and the other end is called 5 prime(5’) end.
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30.  The two chains are arranged in anti parallel manner.
That is, the 5’end of one chain lies close to the 3’end
of the other chain.
 A gene represents a segment of one polynucleotide
chain in the duplex DNA. It is transcribed into an
mRNA that is in turn translated into a protein. This
protein is the product of expression of the gene.
 The gene contain information for a polypeptide chain
(protein). The polypeptide chain consists of sequence
of amino acids.
 The sequence of amino acids in a polypeptide chain is
specified by the sequence of nucleotide in the gene.
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31.  Each amino acids is specified by 3 nucleotides of the
gene. These three nucleotides of a gene are called a
codon or triplet.
 The number of codons in a gene depends on the
number of amino acids in a polypeptide chain.
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32.  If the polypeptide chain contains 100 amino acids, the
gene has 100 codons made up of 300 nucleotides.
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33. Ultra Structure of Gene
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51. Thank
You
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