Lecture 1 - Conjugation | Genetics (Zoology) by ILLL, DU - Biotechnology Engineering (BT) PDF Download

 Page 1


 Conjugation  
1 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
Genetics 
Lesson: Conjugation 
Lesson Name: Dr. Shailly Anand and 
Dr. Jasvinder Kaur 
Lesson Reviewer: Dr. Shashi Chawla 
College/Dept: Molecular Biology Laboratory, Department 
of Zoology, 
University of Delhi 
 
 
 
 
 
 
 
 
 
Page 2


 Conjugation  
1 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
Genetics 
Lesson: Conjugation 
Lesson Name: Dr. Shailly Anand and 
Dr. Jasvinder Kaur 
Lesson Reviewer: Dr. Shashi Chawla 
College/Dept: Molecular Biology Laboratory, Department 
of Zoology, 
University of Delhi 
 
 
 
 
 
 
 
 
 
 Conjugation  
2 
Institute of Lifelong Learning, University of Delhi 
Table of Contents 
? Introduction 
? Historical background 
? Discovery: Joshua Lederberg & Edward Tatum (1946) 
? Conjugation requires physical contact: Bernard Davis  
? Discovery of Fertility factor (F factor): William Hayes (1953) 
? Conjugation: The Process  
? Requirements for the process of conjugation 
? Structure and Function of F plasmid 
? Hfr Strain 
? Hfr/ F
–
 mating: Formation of F
–
 cells 
? Hfr/ F
–
 mating: Formation of F? cells 
? Importance of Conjugation in bacteria 
? Tripartite mating 
? Summary 
? Glossary 
? Practice Questions 
? Answer to the Questions 
? References 
 
 
 
 
 
 
Page 3


 Conjugation  
1 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
Genetics 
Lesson: Conjugation 
Lesson Name: Dr. Shailly Anand and 
Dr. Jasvinder Kaur 
Lesson Reviewer: Dr. Shashi Chawla 
College/Dept: Molecular Biology Laboratory, Department 
of Zoology, 
University of Delhi 
 
 
 
 
 
 
 
 
 
 Conjugation  
2 
Institute of Lifelong Learning, University of Delhi 
Table of Contents 
? Introduction 
? Historical background 
? Discovery: Joshua Lederberg & Edward Tatum (1946) 
? Conjugation requires physical contact: Bernard Davis  
? Discovery of Fertility factor (F factor): William Hayes (1953) 
? Conjugation: The Process  
? Requirements for the process of conjugation 
? Structure and Function of F plasmid 
? Hfr Strain 
? Hfr/ F
–
 mating: Formation of F
–
 cells 
? Hfr/ F
–
 mating: Formation of F? cells 
? Importance of Conjugation in bacteria 
? Tripartite mating 
? Summary 
? Glossary 
? Practice Questions 
? Answer to the Questions 
? References 
 
 
 
 
 
 
 Conjugation  
3 
Institute of Lifelong Learning, University of Delhi 
Introduction 
Genetic recombination in eukaryotes refers to the 
process of crossing over occurring during the 
meiotic phase of cell division. But in context to the 
bacterial population, it commonly denotes the 
replacement or exchange of genes between one cell 
and another. Thus in a sense, both have the same 
effect i.e. transferring of genetic information and 
creation of a cell with an altered genotype. 
This chapter deals with the study of recombination 
events in bacteria which primarily occurs due to any 
of the three ways namely - Conjugation, 
Transformation and Transduction. These form 
the basis of origin of genetic variations that have 
been profoundly studied in the members of the 
same species. Genetic information that is 
transferred between members of the same species 
is known as Vertical Gene Transfer. For example, 
the inheritance of traits/ features from father to son. 
But if the transfer occurs between closely related 
species, it is referred to as the Horizontal Gene 
Transfer. The latter has been commonly observed 
in bacterial species. There are many evidences for 
the acquisition of genes involved in biodegradation 
of many xenobiotics in diverse groups of bacterial 
species. Examples include lindane degradation, 
phenol degradation etc. 
 
 
 
 
Food for Bacteria: Culture 
Medium 
Bacteria grow either in liquid media or 
on solid media containing agar in 
petridish. The culture media 
containing simple organic source of 
carbon along with inorganic ions is 
commonly termed as the minimal 
medium. Based on the ability of 
bacteria to survive on such a medium, 
they can either be prototrophs or 
auxotrophs. The wild type bacterial 
strain that grows on minimal media 
and is capable of synthesizing all the 
essential compounds is called as the 
prototrophs. On the other hand, 
bacteria that are unable to synthesize 
one or many of such organic 
compounds making them incapable of 
growing on minimal media unless the 
specific compound is supplemented 
are termed as auxotrophs. Contrary 
to the minimal medium is the 
complete medium that contains all 
the components in extensive 
quantities for a flourishing growth. 
Page 4


 Conjugation  
1 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
Genetics 
Lesson: Conjugation 
Lesson Name: Dr. Shailly Anand and 
Dr. Jasvinder Kaur 
Lesson Reviewer: Dr. Shashi Chawla 
College/Dept: Molecular Biology Laboratory, Department 
of Zoology, 
University of Delhi 
 
 
 
 
 
 
 
 
 
 Conjugation  
2 
Institute of Lifelong Learning, University of Delhi 
Table of Contents 
? Introduction 
? Historical background 
? Discovery: Joshua Lederberg & Edward Tatum (1946) 
? Conjugation requires physical contact: Bernard Davis  
? Discovery of Fertility factor (F factor): William Hayes (1953) 
? Conjugation: The Process  
? Requirements for the process of conjugation 
? Structure and Function of F plasmid 
? Hfr Strain 
? Hfr/ F
–
 mating: Formation of F
–
 cells 
? Hfr/ F
–
 mating: Formation of F? cells 
? Importance of Conjugation in bacteria 
? Tripartite mating 
? Summary 
? Glossary 
? Practice Questions 
? Answer to the Questions 
? References 
 
 
 
 
 
 
 Conjugation  
3 
Institute of Lifelong Learning, University of Delhi 
Introduction 
Genetic recombination in eukaryotes refers to the 
process of crossing over occurring during the 
meiotic phase of cell division. But in context to the 
bacterial population, it commonly denotes the 
replacement or exchange of genes between one cell 
and another. Thus in a sense, both have the same 
effect i.e. transferring of genetic information and 
creation of a cell with an altered genotype. 
This chapter deals with the study of recombination 
events in bacteria which primarily occurs due to any 
of the three ways namely - Conjugation, 
Transformation and Transduction. These form 
the basis of origin of genetic variations that have 
been profoundly studied in the members of the 
same species. Genetic information that is 
transferred between members of the same species 
is known as Vertical Gene Transfer. For example, 
the inheritance of traits/ features from father to son. 
But if the transfer occurs between closely related 
species, it is referred to as the Horizontal Gene 
Transfer. The latter has been commonly observed 
in bacterial species. There are many evidences for 
the acquisition of genes involved in biodegradation 
of many xenobiotics in diverse groups of bacterial 
species. Examples include lindane degradation, 
phenol degradation etc. 
 
 
 
 
Food for Bacteria: Culture 
Medium 
Bacteria grow either in liquid media or 
on solid media containing agar in 
petridish. The culture media 
containing simple organic source of 
carbon along with inorganic ions is 
commonly termed as the minimal 
medium. Based on the ability of 
bacteria to survive on such a medium, 
they can either be prototrophs or 
auxotrophs. The wild type bacterial 
strain that grows on minimal media 
and is capable of synthesizing all the 
essential compounds is called as the 
prototrophs. On the other hand, 
bacteria that are unable to synthesize 
one or many of such organic 
compounds making them incapable of 
growing on minimal media unless the 
specific compound is supplemented 
are termed as auxotrophs. Contrary 
to the minimal medium is the 
complete medium that contains all 
the components in extensive 
quantities for a flourishing growth. 
 Conjugation  
4 
Institute of Lifelong Learning, University of Delhi 
Historical background 
Discovery: Joshua Lederberg & Edward Tatum (1946) 
They pioneered the study on genetic recombination in bacteria and concluded that bacteria 
undergo the process of gene transfer by way of conjugation. They experimentally 
demonstrated the process using two auxotroph strains of Escherichia coli K12 denoted by 
Strain A and Strain B. Strain A could synthesize Threonine (thr), Leucine (leu) and Thiamine 
(thi) but not Methionine (met) and Biotin (bio). Therefore, Strain A was grown in a minimal 
media supplemented with methionine and biotin and were designated as met
- 
bio
- 
thr
+ 
leu
+ 
thi
+
. Strain B could synthesize methionine and biotin but not others and therefore was 
grown in minimal media containing thr, leu and thi. Hence, Strain B was designated as met
+ 
bio
+ 
thr
- 
leu
- 
thi
-
. These (met 
 
bio
  
thr
  
leu 
 
thi) are called genetic markers and help in 
distinguishing one bacterial strain from another. 
Three experimental set ups were prepared as under: 
Experiment 1: (Control) Culture of Strain A was plated on minimal medium. 
Experiment 2: (Control) Culture of Strain B was plated on minimal medium. 
Experiment 3: Culture of Strain A and B was mixed together and incubated at optimum 
condition. It was then plated on minimal medium. 
Upon incubation it was observed that in case of experiment 1 and 2, no growth was seen on 
the plates while in case of experiment 3, a few colonies appeared (1 in every 10
7
 cells). 
These prototrophs could thus synthesize all the components required for the growth and 
survival and represented met
+ 
bio
+ 
thr
+ 
leu
+ 
thi
+
. (Fig. 1) 
Conclusion: This can be attributed to the ability of a few cells to exchange genetic 
material. This must have led to the ability of the transformed cell to synthesize all 
components. Some form of recombination of genes took place between the two strains. 
 
Did you know? 
Joshua Lederberg was only 20 years old when he proposed this experiment. In the initial 
experiments, he was successful and within a short time of just six months he proved the 
process of bacterial mating (conjugation). 
Page 5


 Conjugation  
1 
Institute of Lifelong Learning, University of Delhi 
 
 
 
 
 
 
Genetics 
Lesson: Conjugation 
Lesson Name: Dr. Shailly Anand and 
Dr. Jasvinder Kaur 
Lesson Reviewer: Dr. Shashi Chawla 
College/Dept: Molecular Biology Laboratory, Department 
of Zoology, 
University of Delhi 
 
 
 
 
 
 
 
 
 
 Conjugation  
2 
Institute of Lifelong Learning, University of Delhi 
Table of Contents 
? Introduction 
? Historical background 
? Discovery: Joshua Lederberg & Edward Tatum (1946) 
? Conjugation requires physical contact: Bernard Davis  
? Discovery of Fertility factor (F factor): William Hayes (1953) 
? Conjugation: The Process  
? Requirements for the process of conjugation 
? Structure and Function of F plasmid 
? Hfr Strain 
? Hfr/ F
–
 mating: Formation of F
–
 cells 
? Hfr/ F
–
 mating: Formation of F? cells 
? Importance of Conjugation in bacteria 
? Tripartite mating 
? Summary 
? Glossary 
? Practice Questions 
? Answer to the Questions 
? References 
 
 
 
 
 
 
 Conjugation  
3 
Institute of Lifelong Learning, University of Delhi 
Introduction 
Genetic recombination in eukaryotes refers to the 
process of crossing over occurring during the 
meiotic phase of cell division. But in context to the 
bacterial population, it commonly denotes the 
replacement or exchange of genes between one cell 
and another. Thus in a sense, both have the same 
effect i.e. transferring of genetic information and 
creation of a cell with an altered genotype. 
This chapter deals with the study of recombination 
events in bacteria which primarily occurs due to any 
of the three ways namely - Conjugation, 
Transformation and Transduction. These form 
the basis of origin of genetic variations that have 
been profoundly studied in the members of the 
same species. Genetic information that is 
transferred between members of the same species 
is known as Vertical Gene Transfer. For example, 
the inheritance of traits/ features from father to son. 
But if the transfer occurs between closely related 
species, it is referred to as the Horizontal Gene 
Transfer. The latter has been commonly observed 
in bacterial species. There are many evidences for 
the acquisition of genes involved in biodegradation 
of many xenobiotics in diverse groups of bacterial 
species. Examples include lindane degradation, 
phenol degradation etc. 
 
 
 
 
Food for Bacteria: Culture 
Medium 
Bacteria grow either in liquid media or 
on solid media containing agar in 
petridish. The culture media 
containing simple organic source of 
carbon along with inorganic ions is 
commonly termed as the minimal 
medium. Based on the ability of 
bacteria to survive on such a medium, 
they can either be prototrophs or 
auxotrophs. The wild type bacterial 
strain that grows on minimal media 
and is capable of synthesizing all the 
essential compounds is called as the 
prototrophs. On the other hand, 
bacteria that are unable to synthesize 
one or many of such organic 
compounds making them incapable of 
growing on minimal media unless the 
specific compound is supplemented 
are termed as auxotrophs. Contrary 
to the minimal medium is the 
complete medium that contains all 
the components in extensive 
quantities for a flourishing growth. 
 Conjugation  
4 
Institute of Lifelong Learning, University of Delhi 
Historical background 
Discovery: Joshua Lederberg & Edward Tatum (1946) 
They pioneered the study on genetic recombination in bacteria and concluded that bacteria 
undergo the process of gene transfer by way of conjugation. They experimentally 
demonstrated the process using two auxotroph strains of Escherichia coli K12 denoted by 
Strain A and Strain B. Strain A could synthesize Threonine (thr), Leucine (leu) and Thiamine 
(thi) but not Methionine (met) and Biotin (bio). Therefore, Strain A was grown in a minimal 
media supplemented with methionine and biotin and were designated as met
- 
bio
- 
thr
+ 
leu
+ 
thi
+
. Strain B could synthesize methionine and biotin but not others and therefore was 
grown in minimal media containing thr, leu and thi. Hence, Strain B was designated as met
+ 
bio
+ 
thr
- 
leu
- 
thi
-
. These (met 
 
bio
  
thr
  
leu 
 
thi) are called genetic markers and help in 
distinguishing one bacterial strain from another. 
Three experimental set ups were prepared as under: 
Experiment 1: (Control) Culture of Strain A was plated on minimal medium. 
Experiment 2: (Control) Culture of Strain B was plated on minimal medium. 
Experiment 3: Culture of Strain A and B was mixed together and incubated at optimum 
condition. It was then plated on minimal medium. 
Upon incubation it was observed that in case of experiment 1 and 2, no growth was seen on 
the plates while in case of experiment 3, a few colonies appeared (1 in every 10
7
 cells). 
These prototrophs could thus synthesize all the components required for the growth and 
survival and represented met
+ 
bio
+ 
thr
+ 
leu
+ 
thi
+
. (Fig. 1) 
Conclusion: This can be attributed to the ability of a few cells to exchange genetic 
material. This must have led to the ability of the transformed cell to synthesize all 
components. Some form of recombination of genes took place between the two strains. 
 
Did you know? 
Joshua Lederberg was only 20 years old when he proposed this experiment. In the initial 
experiments, he was successful and within a short time of just six months he proved the 
process of bacterial mating (conjugation). 
 Conjugation  
5 
Institute of Lifelong Learning, University of Delhi 
 
Figure 1: Discovery of Conjugation by Joshua Lederberg and Edward Tatum (1946) – 
Escherichia coli K12 auxotrophic STRAIN A (met
-
 bio
-
 thr
+
 leu
+
 thi
+
) and STRAIN B (met
+
 
bio
+
 thr
-
 leu
-
 thi
-
) were plated on minimal medium and incubated overnight (CONTROL). 
Also STRAIN A and B were mixed together and when plated on minimal medium resulted in 
prototrophs.  
Source: Author