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GNDU Question Paper-2024
Bachelor of Computer Application (BCA) (Hons.)
5
th
Semester (Batch 2024-28) (CBGS)
ZOOLOGY: Paper-Zoo-V (B)
Time Allowed: Three Hours Max. Marks:35
Note: Attempt Five questions in all, selecting at least One question from each section. The
Fifth question may be attempted from any section. All questions carry equal marks.
SECTION-A
1. Write notes on the following:
(a) Inheritance of skin colour in man.
(b) Lethal Factors.
2. What is crossing over? Explain its cytological basis.
SECTION-B
3. Write a note on the process of transcription of DNA.
4. Explain the following:
(a) Properties of genetic code
(b) Split and overlapping genes.
SECTION-C
5. Describe the regulation of gene expression in Prokaryotes.
6. Write short notes on the following:
(a) Albinism
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(b) Kappa particles in Paramecium.
SECTION-D
7. Write a note on genetic cloning and discuss its application in medicine and agriculture.
8. Explain the following:
(a) Transformation
(b) DNA fingerprinting.
GNDU Question Paper-2024
Bachelor of Computer Application (BCA) (Hons.)
5
th
Semester (Batch 2024-28) (CBGS)
ZOOLOGY: Paper-Zoo-V (B)
Time Allowed: Three Hours Max. Marks:35
Note: Attempt Five questions in all, selecting at least One question from each section. The
Fifth question may be attempted from any section. All questions carry equal marks.
SECTION-A
1. Write notes on the following:
(a) Inheritance of skin colour in man.
(b) Lethal Factors.
Ans: 1(a) Inheritance of Skin Colour in Man
Introduction
The color of human skin is one of the best examples of polygenic inheritance, also known as
quantitative inheritance. Unlike traits such as blood group, which are controlled by a single
gene, skin color is influenced by many genes working together. Because several genes
contribute to the final skin color, there are many shades ranging from very light to very
dark.
The main pigment responsible for skin color is melanin, which is produced by special cells
called melanocytes. The amount of melanin produced depends on the genes inherited from
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both parents. Environmental factors, such as sunlight, can temporarily increase melanin
production (causing tanning), but a person's basic skin color is determined by genetics.
What is Polygenic Inheritance?
Polygenic inheritance means that one characteristic is controlled by two or more pairs of
genes. Each dominant gene contributes a small amount to the trait, while recessive genes
contribute little or nothing.
For skin color, scientists often explain the concept using three pairs of genes:
A/a
B/b
C/c
Each dominant allele (A, B, C) adds more melanin.
Each recessive allele (a, b, c) adds little or no melanin.
The more dominant alleles a person has, the darker the skin.
Example
Suppose:
Very dark parent = AABBCC
Very fair parent = aabbcc
When these two parents have children:
Parents
Dark Parent × Fair Parent
AABBCC aabbcc
F₁ Generation
All Offspring = AaBbCc
These children have a medium (intermediate) skin color because they inherit half dominant
and half recessive genes.
F₂ Generation
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When two F₁ individuals (AaBbCc × AaBbCc) marry, many different gene combinations
appear.
The offspring show seven different shades of skin color, from very fair to very dark.
Very Fair ←──────────────────────────────→ Very Dark
aabbcc
│
Aabbcc
│
AaBbcc
│
AaBbCc (Medium)
│
AABbCc
│
AABBCc
│
AABBCC
This continuous variation explains why brothers and sisters may have different skin tones
even though they have the same parents.
Key Concepts
1. Melanin
Melanin is the natural pigment that gives color to the skin, hair, and eyes. More melanin
means darker skin.
2. Dominant Genes
Dominant genes increase melanin production. Every dominant allele contributes a small
amount of darkness.
3. Recessive Genes
Recessive genes contribute very little or no melanin.
4. Continuous Variation
Since many genes are involved, skin color does not fall into only two categories. Instead, it
forms a continuous range from very fair to very dark.
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Characteristics of Skin Colour Inheritance
Controlled by multiple genes (polygenic inheritance).
Dominant genes have an additive effect.
Produces continuous variation.
Environmental factors like sunlight can influence appearance but do not change
inherited genes.
Children usually have skin color between that of their parents but may resemble
either parent more closely depending on gene combinations.
Conclusion
Inheritance of skin color in humans is a classic example of polygenic inheritance. Multiple
genes together determine how much melanin is produced. Each dominant gene increases
melanin, resulting in darker skin. This is why people show a wide range of natural skin colors
and why siblings can have different shades. Skin color demonstrates how several genes can
work together to produce continuous variation in a population.
1(b) Lethal Factors
Introduction
Lethal factors (or lethal genes) are genes that can cause the death of an organism when
present in a particular genetic combination. The word "lethal" means deadly. These genes
may allow an organism to survive in one form but become fatal in another.
Some lethal genes act before birth, while others may cause death during childhood or later
in life.
What are Lethal Factors?
A lethal factor is a gene that reduces survival or causes death when inherited in a certain
genotype.
Most commonly:
Individuals with heterozygous genotype (Aa) survive.
Individuals with homozygous dominant (AA) or homozygous recessive (aa) may die,
depending on the type of lethal gene.
Thus, lethal genes affect the normal survival of an organism.
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Types of Lethal Factors
1. Recessive Lethal Genes
A recessive lethal gene causes death only when present in the homozygous recessive (aa)
condition.
Example:
Tay-Sachs disease in humans.
Some affected babies die in early childhood due to severe nervous system damage.
2. Dominant Lethal Genes
A dominant lethal gene causes death even if only one copy is present.
Example:
Huntington's disease.
Symptoms usually appear after the age of 3540 years, allowing affected individuals
to reproduce before the disease develops.
Classical Example: Yellow Coat Colour in Mice
This is one of the most famous examples of a lethal gene.
Let:
Y = Yellow coat (dominant)
y = Normal coat (recessive)
However,
YY = Lethal (dies before birth)
Yy = Yellow mouse
yy = Normal mouse
Cross
Yellow × Yellow
Yy × Yy
Punnett Square
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Y
y
Y
YY (Dies)
Yy (Yellow)
y
Yy (Yellow)
yy (Normal)
Among living offspring:
2 Yellow
1 Normal
Instead of the usual 3 : 1 ratio, the observed ratio becomes 2 : 1 because the YY offspring
die before birth.
Characteristics of Lethal Factors
Cause death in specific genetic combinations.
Can be dominant or recessive.
Change the expected Mendelian inheritance ratio.
Some lethal genes act before birth, while others act later in life.
They reduce the survival rate of affected individuals.
Importance of Studying Lethal Factors
Understanding lethal genes helps scientists and doctors:
Identify inherited genetic disorders.
Provide genetic counselling to families.
Predict the chances of inherited diseases.
Improve medical diagnosis and treatment.
Understand patterns of inheritance in genetics.
Conclusion
Lethal factors are genes that can cause death when present in certain genetic combinations.
They may be dominant or recessive and often alter the normal Mendelian ratios. The yellow
coat color in mice is a classic example, where the homozygous dominant genotype (YY) is
lethal, resulting in a 2:1 ratio among surviving offspring. Studying lethal factors is important
because it helps explain genetic diseases, improves our understanding of inheritance, and
supports better healthcare through genetic counselling.
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2. What is crossing over? Explain its cytological basis.
Ans: 2. What is Crossing Over? Explain its Cytological Basis.
Introduction
Crossing over is one of the most important events in genetics because it creates genetic
variation (differences among individuals). It occurs during the formation of gametes (sperm
and egg cells) through a special type of cell division called meiosis.
Imagine two students exchanging a few pages from their notebooks before an exam. After
exchanging the pages, both notebooks contain some original pages and some pages from
the other student. Similarly, during crossing over, two homologous chromosomes exchange
corresponding segments of DNA. As a result, new combinations of genes are formed,
making every offspring genetically unique.
What is Crossing Over?
Crossing over is the exchange of corresponding DNA segments between non-sister
chromatids of homologous chromosomes during Prophase I (Pachytene stage) of meiosis.
It occurs only between homologous chromosomes (one chromosome inherited from
the mother and one from the father).
The exchanged parts contain genes.
This exchange creates new gene combinations, increasing genetic diversity.
Simple Example
Suppose:
Mother's chromosome has genes: A B C D
Father's chromosome has genes: a b c d
After crossing over:
Chromosome 1 → A B c d
Chromosome 2 → a b C D
Now both chromosomes carry a mixture of maternal and paternal genes.
Cytological Basis of Crossing Over
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The cytological basis means the cellular events that can be observed under a microscope
during crossing over.
Crossing over takes place during Prophase I of meiosis, especially in the Pachytene stage.
Step 1: Pairing of Homologous Chromosomes (Synapsis)
At the beginning of Prophase I, homologous chromosomes come close together and pair
with each other.
This pairing is called synapsis.
The paired chromosomes form a structure called a bivalent.
Since each chromosome has two chromatids, the bivalent contains four chromatids,
also called a tetrad.
Step 2: Formation of Synaptonemal Complex
A protein structure called the synaptonemal complex forms between homologous
chromosomes.
Its functions are:
Holds homologous chromosomes together.
Aligns corresponding genes accurately.
Makes crossing over possible.
Step 3: Breaking of DNA
Special enzymes make small cuts in the DNA of non-sister chromatids.
These breaks occur at the same position on both homologous chromosomes.
Step 4: Exchange of Chromosome Segments
The broken DNA ends exchange equivalent segments.
The DNA is then joined again by repair enzymes.
This produces recombinant chromatids, which contain genes from both parents.
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Step 5: Formation of Chiasma
After the exchange, homologous chromosomes begin separating but remain attached at the
crossing point.
This visible X-shaped point is called a chiasma (plural: chiasmata).
The chiasma is direct evidence that crossing over has occurred.
Step 6: Separation of Chromosomes
During later stages of meiosis:
Homologous chromosomes separate.
Each gamete receives chromosomes carrying new combinations of genes.
Thus, every gamete becomes genetically different.
Stages of Meiosis Related to Crossing Over
Stage
Event
Leptotene
Chromosomes become visible
Zygotene
Homologous chromosomes pair (Synapsis)
Pachytene
Crossing over occurs
Diplotene
Chiasmata become visible
Diakinesis
Chiasmata move toward chromosome ends
Simple Diagram
Before Crossing Over
Maternal Chromosome
A ─ B ─ C ─ D
│ │
│ │
a ─ b ─ c ─ d
Paternal Chromosome
↓ Crossing Over
After Crossing Over
A ─ B ─ c ─ d
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a ─ b ─ C ─ D
Chiasma Formation
Before
==========
==========
During Crossing Over
====X=====
====X=====
After
===\ /====
====X=====
===/ \====
The X-shaped point is called the Chiasma, where DNA exchange occurs.
Importance of Crossing Over
Crossing over has several important biological functions:
Creates genetic variation among offspring.
Produces new combinations of genes.
Helps organisms adapt to changing environments.
Increases the chances of evolution through natural selection.
Ensures proper separation of homologous chromosomes during meiosis.
Reduces the chance of inherited genetic abnormalities caused by improper
chromosome segregation.
Key Terms
Homologous chromosomes: Pair of chromosomes with the same genes, one
inherited from each parent.
Chromatid: One of the two identical copies of a replicated chromosome.
Non-sister chromatids: Chromatids belonging to different homologous
chromosomes.
Synapsis: Pairing of homologous chromosomes.
Tetrad: Four chromatids formed when homologous chromosomes pair.
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Synaptonemal complex: Protein structure that holds homologous chromosomes
together.
Chiasma: The visible point where crossing over occurs.
Conclusion
Crossing over is the exchange of genetic material between non-sister chromatids of
homologous chromosomes during the Pachytene stage of Prophase I in meiosis. Its
cytological basis includes synapsis, formation of the synaptonemal complex, DNA breakage
and exchange, and the appearance of chiasmata. This process creates genetic
recombination, making each gamete genetically unique and increasing variation in
offspring. Genetic variation is essential for adaptation, evolution, and the long-term
survival of species, making crossing over one of the most significant events in heredity.
SECTION-B
3. Write a note on the process of transcription of DNA.
Ans: 3. Write a Note on the Process of Transcription of DNA
Introduction
Transcription is the first step of gene expression, where the genetic information stored in
DNA is copied into RNA. Think of DNA as a huge instruction book kept safely inside the
nucleus of a cell. Since the original book cannot leave the nucleus, the cell makes a working
copy of the required information. This copy is called messenger RNA (mRNA). The mRNA
then carries the instructions to ribosomes, where proteins are made.
In simple words, transcription means copying the genetic message from DNA into RNA. It is
an essential process because proteins, which perform most functions in our body, are made
according to the instructions carried by mRNA.
Definition
Transcription is the biological process in which the information present in one strand of
DNA is copied into a complementary RNA molecule by the enzyme RNA polymerase.
Why is Transcription Important?
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It converts DNA information into RNA.
It is the first step in protein synthesis.
It helps cells produce proteins needed for growth, repair, and metabolism.
It allows genes to be expressed only when required.
Main Components Involved
1. DNA (Template Strand)
DNA contains the genetic code. During transcription, only one strand of DNA acts as the
template strand, while the other is called the coding strand.
2. RNA Polymerase
RNA polymerase is the main enzyme responsible for transcription. It reads the DNA
template and joins RNA nucleotides together to form an RNA strand.
3. RNA Nucleotides
RNA is made of four nitrogen bases:
Adenine (A)
Uracil (U) (instead of Thymine)
Cytosine (C)
Guanine (G)
The base-pairing rules are:
DNA A → RNA U
DNA T → RNA A
DNA G → RNA C
DNA C → RNA G
Steps of DNA Transcription
1. Initiation (Starting the Process)
RNA polymerase attaches to a specific DNA sequence called the promoter.
The DNA double helix unwinds and opens.
One DNA strand becomes the template strand.
This step marks the beginning of transcription.
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2. Elongation (Building the RNA Strand)
RNA polymerase moves along the DNA template strand.
It reads the DNA bases one by one.
Complementary RNA nucleotides are added.
For example:
DNA Template : A T G C C A
RNA Produced : U A C G G U
The RNA strand becomes longer as more nucleotides are added.
3. Termination (Stopping the Process)
RNA polymerase reaches a termination sequence on DNA.
The enzyme stops working.
The completed RNA molecule is released.
DNA closes back into its double-helix structure.
The newly formed RNA then leaves for further processing (in eukaryotic cells) or directly
participates in protein synthesis (in prokaryotic cells).
Simple Diagram of Transcription
DNA Double Strand
---------------------------------
Coding Strand: A T G C C A G T
| | | | | | |
Template Strand: T A C G G T C A
↑
RNA Polymerase
│
▼
mRNA: A U G C C A G U
Stages at a Glance
DNA
│
▼
Initiation
(RNA Polymerase binds promoter)
│
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▼
Elongation
(RNA strand is synthesized)
│
▼
Termination
(RNA released)
│
▼
mRNA
│
▼
Protein Synthesis
Transcription in Eukaryotes
In plants and animals (eukaryotes), the newly formed RNA is called pre-mRNA. Before it is
ready for protein synthesis, it undergoes three important modifications:
5 Cap is added to protect the RNA.
Poly-A Tail is added at the end to increase stability.
Splicing removes non-coding regions (introns) and joins coding regions (exons).
After these changes, the mature mRNA leaves the nucleus and reaches the ribosome.
Difference Between DNA and RNA
DNA
RNA
Double-stranded
Single-stranded
Contains Thymine (T)
Contains Uracil (U)
Stores genetic information
Carries genetic message
Remains in the nucleus
Travels to ribosomes
Key Points to Remember
Transcription is the first step of gene expression.
It copies information from DNA to mRNA.
The enzyme responsible is RNA polymerase.
It occurs in three stages: Initiation, Elongation, and Termination.
RNA uses Uracil (U) instead of Thymine (T).
In eukaryotes, pre-mRNA is modified before becoming mature mRNA.
The produced mRNA carries genetic instructions for protein synthesis.
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Conclusion
Transcription is one of the most important biological processes because it allows the genetic
information stored safely in DNA to be used without altering the original DNA molecule.
During transcription, RNA polymerase copies the genetic code from the DNA template into
messenger RNA (mRNA) through the three stages of initiation, elongation, and
termination. In eukaryotic cells, the RNA is further processed before leaving the nucleus.
The final mRNA carries the instructions to ribosomes, where proteins are produced. Thus,
transcription acts as the essential link between DNA and protein synthesis, making it
fundamental for cell growth, repair, development, and the normal functioning of all living
organisms.
4. Explain the following:
(a) Properties of genetic code
(b) Split and overlapping genes.
Ans: 4. Explain the following:
(a) Properties of Genetic Code
The genetic code is like the language of life. Imagine that DNA is a huge instruction book for
building and running the human body. However, the body cannot read DNA directly.
Instead, the information is copied into mRNA, and the cell reads this message in groups of
three letters, called codons. Each codon tells the cell which amino acid should be added to
build a protein. Since proteins control almost every function in the body, the genetic code is
extremely important.
Simple Diagram
DNA
│
▼
mRNA: AUG | GCU | UUU | GGA
│ │ │ │
▼ ▼ ▼ ▼
Methionine Alanine Phenylalanine Glycine
↓
Protein Formation
Properties of the Genetic Code
1. Triplet Code
Each codon is made of three nucleotides (bases).
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Example:
AUG → Methionine
GCU → Alanine
Since there are four bases (A, U, G, C) and each codon contains three bases, there are 64
possible codons (4³ = 64).
2. Unambiguous (Specific)
Each codon specifies only one amino acid.
Example:
UUU always codes for Phenylalanine.
It never codes for any other amino acid.
This prevents confusion during protein synthesis.
3. Degenerate (Redundant)
Many amino acids are coded by more than one codon.
Example:
Leucine is coded by:
UUA
UUG
CUU
CUC
CUA
CUG
This provides protection because a small mutation may not change the amino acid.
4. Universal
Almost all living organismsfrom bacteria to humansuse the same genetic code.
For example:
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AUG means Methionine in humans, plants, and bacteria.
This similarity is strong evidence that all organisms evolved from a common ancestor.
5. Non-Overlapping
Each nucleotide belongs to only one codon.
Example:
AUG GCU UUU
Correct Reading:
AUG | GCU | UUU
Not:
AUG
UGG
GGC
Every codon is read separately.
6. Commaless (Continuous)
There are no commas or spaces between codons.
Example:
AUGGCUUUUGGA
Read as:
AUG | GCU | UUU | GGA
The ribosome reads continuously without stopping.
7. Start Codon
Protein synthesis begins with a start codon.
AUG
AUG codes for Methionine and signals the ribosome to begin protein synthesis.
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8. Stop Codons
Three codons signal the end of protein synthesis.
They are:
UAA
UAG
UGA
These do not code for any amino acid.
9. Colinear
The sequence of codons in mRNA is the same order in which amino acids appear in the
protein.
Example:
Codons:
AUG → GCU → UUU
Protein:
Methionine → Alanine → Phenylalanine
The order remains unchanged.
Summary
The genetic code is a universal, triplet, non-overlapping, commaless, degenerate, and
unambiguous system that ensures proteins are produced accurately. Because of these
properties, cells can faithfully convert genetic information into functional proteins.
(b) Split Genes and Overlapping Genes
Genes are DNA segments that contain instructions for making proteins. Scientists
discovered that not all genes have the same structure. Some genes are interrupted by non-
coding regions, while others share parts of their DNA sequence. These are known as split
genes and overlapping genes.
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1. Split Genes
A split gene is a gene whose coding sequence is interrupted by non-coding regions called
introns.
The useful coding portions are called exons.
During protein synthesis:
1. DNA is copied into pre-mRNA.
2. Both exons and introns are present.
3. Introns are removed by RNA splicing.
4. Exons join together to form mature mRNA.
5. The mature mRNA is translated into protein.
Diagram
DNA Gene
Exon1 -- Intron -- Exon2 -- Intron -- Exon3
│
▼
pre-mRNA
│
RNA Splicing
(Removes Introns)
▼
Exon1 -------- Exon2 -------- Exon3
▼
Mature mRNA
▼
Protein
Key Points
Found mainly in eukaryotes (humans, plants, animals).
Introns do not code for proteins.
Exons contain the actual genetic information.
RNA splicing removes introns before translation.
Split genes allow alternative splicing, enabling one gene to produce different
proteins.
Importance
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Increases protein diversity.
Helps regulate gene expression.
Plays an important role in evolution.
2. Overlapping Genes
Overlapping genes are genes in which one region of DNA is shared by two different genes.
The same DNA sequence can produce different proteins because the genes are read in
different reading frames or from different starting points.
Diagram
DNA Sequence
ATGAAACCCGGGTTT
Gene A:
ATG | AAA | CCC | GGG
Gene B:
TGA | AAC | CCG | GGT
Same DNA
Different Reading Frames
Different Proteins
Key Points
Common in viruses and some bacteria.
Rare in humans.
Saves DNA space by storing more information in a small genome.
One DNA segment can contribute to multiple proteins.
Importance
Makes the genome compact and efficient.
Allows viruses to carry more genetic information despite having very small genomes.
Increases coding efficiency.
Difference Between Split Genes and Overlapping Genes
Split Genes
Overlapping Genes
Contain introns and exons
Two genes share the same DNA sequence
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Introns are removed by RNA splicing
Shared DNA is read in different reading frames
Common in eukaryotes
Common in viruses and some bacteria
Increase protein diversity through
splicing
Save genome space by encoding multiple
proteins
Conclusion
The genetic code is the precise language through which cells convert DNA information into
proteins. Its propertiessuch as being triplet, universal, unambiguous, degenerate, non-
overlapping, and commalessensure accurate protein synthesis in all living organisms.
Split genes demonstrate how eukaryotic organisms organize genes into exons and introns,
with RNA splicing producing mature messenger RNA before protein synthesis. In contrast,
overlapping genes maximize the use of limited DNA by allowing two different genes to
share the same nucleotide sequence, a feature commonly seen in viruses. Together, these
concepts highlight the remarkable efficiency and complexity of genetic organization and
explain how living organisms store, regulate, and express genetic information.
SECTION-C
5. Describe the regulation of gene expression in Prokaryotes.
Ans: 5. Describe the Regulation of Gene Expression in Prokaryotes
Gene expression is the process by which the information stored in a gene is used to make
proteins. Proteins are essential because they perform almost every function in a cell.
However, a cell does not need to produce every protein all the time. Instead, it makes only
the proteins that are needed at a particular moment. This control of turning genes ON or
OFF is called regulation of gene expression.
In prokaryotes (such as bacteria), gene regulation is simple, fast, and efficient. Since
bacteria live in changing environments, they must quickly adjust to the availability of food,
temperature, or other conditions. Therefore, they regulate gene expression mainly at the
transcription stage (the process of making RNA from DNA).
What is Gene Expression?
Gene expression is the process through which the information in DNA is converted into a
functional product, usually a protein.
The steps are:
DNA → mRNA → Protein
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DNA stores genetic information.
mRNA (Messenger RNA) carries the instructions.
Ribosomes read the mRNA and produce proteins.
If a gene is ON, the protein is produced.
If a gene is OFF, no protein is produced.
Why is Gene Regulation Important?
Gene regulation helps bacteria to:
Save energy by producing only necessary proteins.
Respond quickly to environmental changes.
Adapt to the availability or absence of nutrients.
Ensure proper growth and survival.
For example, if lactose (milk sugar) is not present, bacteria do not waste energy making
enzymes to digest it.
Operon Model The Main Mechanism of Gene Regulation
The regulation of gene expression in prokaryotes is best explained by the Operon Model,
proposed by François Jacob and Jacques Monod.
An operon is a group of related genes that are controlled together by a single promoter and
operator.
Components of an Operon
Regulator Gene
│
▼
Produces Repressor Protein
│
▼
Promoter → Operator → Structural Genes
│
▼
RNA Polymerase
1. Regulator Gene
Produces a repressor protein.
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The repressor controls whether the operon is active or inactive.
2. Promoter
The site where RNA polymerase binds.
RNA polymerase starts transcription from here.
3. Operator
Acts like a switch.
The repressor protein binds here to stop transcription.
4. Structural Genes
These genes contain instructions for making proteins or enzymes.
The Lac Operon (Inducible Operon)
The Lac Operon controls the digestion of lactose in bacteria such as E. coli.
It contains three structural genes:
lacZ → Produces β-galactosidase
lacY → Produces permease
lacA → Produces transacetylase
These enzymes help bacteria use lactose as food.
Case 1: Lactose is Absent
When lactose is not available:
No Lactose
Repressor Protein
│
▼
[Operator]
│
Stops RNA Polymerase
No Transcription
No Enzyme Production
What happens?
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The regulator gene produces a repressor protein.
The repressor binds to the operator.
RNA polymerase cannot move forward.
Structural genes remain OFF.
No enzymes are produced.
This saves energy.
Case 2: Lactose is Present
When lactose enters the bacterial cell:
Lactose Present
Lactose + Repressor
│
▼
Inactive Repressor
Operator is Free
│
RNA Polymerase Moves
│
Transcription Starts
│
Enzymes Produced
What happens?
Lactose acts as an inducer.
It binds to the repressor protein.
The repressor changes shape and leaves the operator.
RNA polymerase can now transcribe the genes.
Enzymes needed to digest lactose are produced.
Thus, the genes are switched ON only when lactose is available.
The Trp Operon (Repressible Operon)
The Trp Operon controls the production of the amino acid tryptophan.
Unlike the lac operon, this operon is normally ON.
When Tryptophan is Low
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Low Tryptophan
Repressor Inactive
│
Operator Free
│
Genes ON
│
Tryptophan Produced
The cell makes tryptophan because it is needed.
When Tryptophan is High
High Tryptophan
Tryptophan + Repressor
│
Active Repressor
│
Operator Blocked
│
Genes OFF
When enough tryptophan is already present, it acts as a co-repressor by activating the
repressor protein. The activated repressor blocks transcription, preventing unnecessary
production of more tryptophan.
Difference Between Lac Operon and Trp Operon
Feature
Lac Operon
Trp Operon
Type
Inducible Operon
Repressible Operon
Normally
OFF
ON
Activated by
Lactose
Low tryptophan levels
Repressed by
Absence of lactose
High tryptophan levels
Function
Breaks down lactose
Produces tryptophan
Key Points to Remember
Gene expression means converting DNA information into proteins.
In prokaryotes, regulation mainly occurs during transcription.
The operon model is the basic mechanism of gene regulation.
An operon contains a promoter, operator, and structural genes.
The lac operon is an inducible operon that turns ON only when lactose is present.
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The trp operon is a repressible operon that turns OFF when tryptophan is abundant.
This regulation allows bacteria to save energy and adapt quickly to changing
environmental conditions.
Conclusion
Regulation of gene expression in prokaryotes is a highly efficient system that ensures
bacteria produce proteins only when they are needed. The operon model, especially the lac
operon and trp operon, demonstrates how genes can be switched ON or OFF in response to
environmental conditions. This ability to regulate gene activity helps bacteria conserve
energy, respond rapidly to nutrient availability, and survive in changing environments.
Understanding gene regulation is fundamental to genetics, microbiology, and biotechnology
because it explains how even simple organisms precisely control their cellular activities.
6. Write short notes on the following:
(a) Albinism
(b) Kappa particles in Paramecium.
Ans: 6. Write Short Notes on:
(a) Albinism
Introduction
Albinism is a genetic (hereditary) condition in which a person or an animal is born with little
or no melanin pigment in the skin, hair, and eyes. Melanin is the natural pigment
responsible for giving color to our body. It also protects the skin from the harmful ultraviolet
(UV) rays of the sun.
Think of melanin as the "natural color paint" of the body. In people with albinism, the body
cannot make enough of this paint because of a mutation (change) in certain genes involved
in melanin production.
What Causes Albinism?
Albinism is caused by an inherited mutation in genes that control the production of
melanin. It is usually passed from parents to children.
The most common reason is a defect in the tyrosinase enzyme, which is needed to convert
the amino acid tyrosine into melanin. Without this enzyme, melanin cannot be produced
properly.
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Simple Flow:
Gene Mutation
↓
Tyrosinase enzyme absent or defective
↓
Melanin production decreases
↓
Skin, Hair and Eyes become very light
Characteristics (Symptoms)
A person with albinism usually has:
Very fair or white skin.
White, pale yellow or light-colored hair.
Blue, gray or pinkish eyes.
Poor eyesight or reduced vision.
Sensitivity to bright light (photophobia).
Rapid eye movements (nystagmus) in many cases.
Higher risk of sunburn and skin cancer because of lack of melanin.
Types of Albinism
There are mainly two important types:
1. Oculocutaneous Albinism (OCA)
Affects the skin, hair, and eyes.
Most common type.
2. Ocular Albinism (OA)
Mainly affects the eyes.
Skin and hair may appear nearly normal.
Can Albinism be Cured?
There is no permanent cure because it is a genetic condition.
However, people with albinism can live healthy lives by:
Wearing sunglasses.
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Using sunscreen.
Protecting themselves from excessive sunlight.
Having regular eye check-ups.
Using corrective glasses if needed.
Importance of Melanin
Melanin is important because it:
Gives color to the body.
Protects the skin from UV radiation.
Helps in normal eye development.
Reduces the risk of skin damage.
Without enough melanin, these protective functions become weaker.
Simple Diagram
Normal Person
Genes
↓
Tyrosinase Enzyme
↓
Melanin Produced
↓
Normal Skin Hair Eyes
Person with Albinism
Gene Mutation
↓
Tyrosinase Defect
↓
Little or No Melanin
↓
White Skin Light Hair Vision Problems
Conclusion
Albinism is an inherited genetic disorder caused by the absence or reduction of melanin
pigment. Although it changes a person's appearance and may cause vision problems and
sensitivity to sunlight, it is not an infectious disease. With proper care, protection from
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sunlight, and regular medical check-ups, individuals with albinism can lead normal and
productive lives.
(b) Kappa Particles in Paramecium
Introduction
Kappa particles are tiny protein-producing symbiotic bacteria found in the cytoplasm of
certain strains of the single-celled organism Paramecium aurelia.
They are famous because they make some Paramecium capable of killing other
Paramecium that do not possess these particles.
For this reason, such Paramecium are called "killer Paramecia."
What is Paramecium?
Paramecium is a microscopic, slipper-shaped unicellular protozoan found in freshwater
ponds and lakes.
It moves with the help of tiny hair-like structures called cilia.
What are Kappa Particles?
Kappa particles are:
Tiny rod-shaped symbiotic bacteria.
Present in the cytoplasm of certain strains of Paramecium aurelia.
Responsible for producing a poisonous protein called Paramecin.
Paramecin is harmless to the Paramecium carrying kappa particles but is deadly to
Paramecia that lack them.
How Do They Work?
The process is very simple.
Paramecium with Kappa Particles
↓
Produces Paramecin (Toxin)
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↓
Toxin Released into Water
↓
Nearby Sensitive Paramecium Die
↓
Killer Paramecium Survives
Why are They Called Killer Paramecia?
A Paramecium containing kappa particles releases paramecin, which kills nearby sensitive
Paramecia.
This provides several advantages:
Less competition for food.
More space for growth.
Better survival.
Therefore, these strains are called killer strains.
Genetic Control
The presence of kappa particles depends upon:
1. A dominant nuclear gene called K.
2. The actual kappa particles present in the cytoplasm.
Both are necessary.
If the K gene is absent, kappa particles cannot survive.
If kappa particles are missing, the Paramecium cannot become a killer even if it has
the K gene.
This is an example of the interaction between nuclear genes and cytoplasmic inheritance.
Biological Importance
Kappa particles are important because they help scientists understand:
Cytoplasmic inheritance.
Symbiosis.
Genecytoplasm interaction.
Microbial competition.
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Evolution of microorganisms.
They are widely studied in genetics because they demonstrate that some inherited
characteristics depend on both nuclear genes and cytoplasmic factors.
Simple Diagram
Killer Paramecium
____________
/ \
| Kappa |
| Particles |
| (Cytoplasm) |
\______________/
↓
Produces Paramecin
↓
Sensitive Paramecium Dies
Key Features of Kappa Particles
Feature
Description
Organism
Paramecium aurelia
Nature
Symbiotic bacteria
Location
Cytoplasm
Product
Paramecin (toxin)
Function
Kills sensitive Paramecia
Genetic Requirement
Dominant K gene and kappa particles
Importance
Example of cytoplasmic inheritance and symbiosis
Conclusion
Kappa particles are microscopic symbiotic bacteria found in the cytoplasm of certain strains
of Paramecium aurelia. They produce the toxin paramecin, allowing these organisms to kill
sensitive Paramecia and reduce competition. Their existence demonstrates the combined
role of nuclear genes and cytoplasmic factors in inheritance, making them an important
topic in genetics and cell biology.
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SECTION-D
7. Write a note on genetic cloning and discuss its application in medicine and agriculture.
Ans: Genetic Cloning: Meaning, Process, and Its Applications in Medicine and Agriculture
Introduction
Genetic cloning is one of the most important achievements of modern biotechnology. The
word "clone" means an exact genetic copy of a living organism, cell, or gene. In simple
words, genetic cloning is the process of creating an identical copy of DNA, cells, or even a
complete organism. Every clone has the same genetic information (DNA) as the original.
Scientists use cloning to study genes, produce medicines, improve crops, and help conserve
endangered animals. It is a powerful technology that has many benefits, but it also raises
ethical and social concerns.
What is Genetic Cloning?
Genetic cloning is the process of making an exact copy of a gene, a cell, or an entire
organism using biotechnology.
There are three main types of cloning:
1. Gene Cloning (DNA Cloning)
Copies a specific gene or DNA segment.
Used in laboratories to study genes and produce useful proteins like insulin.
2. Reproductive Cloning
Produces a complete organism that is genetically identical to another.
Example: Dolly the Sheep, the first cloned mammal (1996).
3. Therapeutic Cloning
Produces stem cells instead of a whole organism.
These stem cells are used to repair damaged tissues and organs.
How Does Genetic Cloning Work?
The basic steps of reproductive cloning are:
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Donor Animal
│
▼
Take Body Cell (contains DNA)
│
▼
Remove Nucleus from Egg Cell
│
▼
Insert Donor DNA into Egg Cell
│
▼
Stimulate Cell Division
│
▼
Embryo Formation
│
▼
Embryo Placed in Surrogate Mother
│
▼
Birth of a Clone
The new organism has almost the same DNA as the donor organism.
Applications of Genetic Cloning in Medicine
Genetic cloning has greatly improved healthcare and medical research.
1. Production of Medicines
Scientists clone useful genes into bacteria or yeast so they can produce important medicines
such as:
Human insulin for diabetes
Human growth hormone
Blood clotting factors
Vaccines
This method produces medicines safely, quickly, and in large quantities.
2. Stem Cell Therapy
Therapeutic cloning creates stem cells that can replace damaged tissues.
It may help treat:
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Parkinson's disease
Alzheimer's disease
Diabetes
Spinal cord injuries
Heart diseases
3. Organ and Tissue Regeneration
Scientists hope cloning can help grow healthy tissues or even organs for transplantation,
reducing organ shortages.
4. Medical Research
Cloned cells allow scientists to study:
Genetic disorders
Cancer
Rare diseases
Drug testing
This helps develop better treatments and medicines.
5. Personalized Medicine
Because cloned tissues match a patient's DNA, there is a lower chance of organ rejection
after transplantation.
Applications of Genetic Cloning in Agriculture
Cloning is also transforming agriculture by improving crop and animal production.
1. Improved Livestock
Healthy animals with desirable traits can be cloned.
Benefits include:
Higher milk production
Better meat quality
Faster growth
Disease resistance
2. Preservation of Valuable Animals
Rare breeds and highly productive animals can be preserved through cloning.
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3. Better Crop Improvement
Gene cloning helps develop crops that:
Resist insects and pests
Tolerate drought
Grow faster
Produce higher yields
Have better nutritional value
4. Disease-Resistant Plants
Scientists clone useful genes to create plants that naturally resist diseases, reducing the
need for chemical pesticides.
5. Conservation of Endangered Species
Cloning technology may help protect endangered animals by increasing their population.
Advantages of Genetic Cloning
Produces genetically identical organisms.
Helps manufacture life-saving medicines.
Improves crop quality and agricultural production.
Supports treatment of many diseases.
Conserves endangered species.
Advances scientific research.
Disadvantages and Ethical Concerns
Although cloning has many benefits, it also has limitations.
Very expensive technology.
High failure rate in cloning experiments.
Some cloned animals suffer health problems.
Ethical and religious concerns about cloning humans.
Reduced genetic diversity may increase disease risk.
Therefore, cloning should be used responsibly and under strict scientific and ethical
guidelines.
Conclusion
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Genetic cloning is a revolutionary biotechnology that allows scientists to create identical
copies of genes, cells, or organisms. It has transformed medicine by enabling the production
of medicines, stem cell therapies, disease research, and the possibility of organ
regeneration. In agriculture, cloning improves livestock, increases crop productivity,
develops disease-resistant plants, and helps conserve endangered species. Despite its
enormous potential, cloning must be used carefully because of ethical issues, high costs,
and biological risks. With responsible use, genetic cloning has the potential to improve
human health, food security, and scientific progress in the future.
8. Explain the following:
(a) Transformation
(b) DNA fingerprinting.
Ans: 8. Explain the following:
(a) Transformation
Transformation is a natural process in which a living cell (usually a bacterium) takes up
foreign DNA from its surroundings and incorporates it into its own genetic material. This
process changes the characteristics of the cell because it receives new genetic information.
In simple words, transformation is like installing new software into a computer, where the
new software gives the computer additional features. Similarly, when a bacterium takes in
DNA from another organism, it may gain new abilities such as resistance to antibiotics or the
ability to produce a new protein.
The phenomenon of transformation was first discovered by the British scientist Frederick
Griffith in 1928 while studying the bacterium Streptococcus pneumoniae, which causes
pneumonia.
Griffith worked with two types of bacteria:
S strain (Smooth strain): Has a protective capsule and causes disease.
R strain (Rough strain): Does not have a capsule and is harmless.
During his experiment:
1. Living S bacteria killed mice.
2. Living R bacteria did not kill mice.
3. Heat-killed S bacteria also did not kill mice.
4. But when heat-killed S bacteria were mixed with living R bacteria, the mice died.
Griffith concluded that some "transforming principle" from the dead S bacteria had entered
the living R bacteria and changed them into harmful S bacteria. Later, scientists Oswald
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Avery, Colin MacLeod, and Maclyn McCarty proved that this transforming principle was
DNA.
Importance of Transformation
Helps bacteria acquire new traits.
Plays an important role in genetic variation.
Widely used in genetic engineering to introduce useful genes into bacteria.
Helps in producing medicines like human insulin, vaccines, and enzymes.
Simple Diagram of Transformation
Dead S Bacteria
│
│ DNA released
▼
Living R Bacteria
│
│ DNA enters cell
▼
Transformed S Bacteria
(Becomes disease-causing)
Easy Example
Imagine your mobile phone receives a software update. Before the update, it could not
perform certain tasks. After installing the update, it gains new features. Similarly, during
transformation, a bacterium receives new DNA and gains new characteristics.
(b) DNA Fingerprinting
DNA fingerprinting is a scientific technique used to identify a person by studying their
unique DNA pattern. Just as every person's fingerprints are unique, the DNA pattern of
every individual (except identical twins) is also unique.
DNA contains the complete genetic information of an organism. Certain regions of DNA
contain repeated sequences called Variable Number Tandem Repeats (VNTRs) or Short
Tandem Repeats (STRs). These repeated sequences vary from one person to another,
making each person's DNA pattern unique.
DNA fingerprinting was developed by Sir Alec Jeffreys in 1984.
Steps of DNA Fingerprinting
1. Collection of Sample
o Blood
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o Hair root
o Saliva
o Skin cells
o Semen
2. DNA Extraction
o DNA is isolated from the collected sample.
3. DNA Amplification
o PCR (Polymerase Chain Reaction) is used to make millions of copies of DNA.
4. Separation of DNA Fragments
o DNA fragments are separated according to size using gel electrophoresis.
5. Analysis
o The banding pattern is examined and compared with another DNA sample.
If the DNA banding patterns match, both samples belong to the same individual or a close
biological relative.
Applications of DNA Fingerprinting
Identification of criminals in forensic science.
Solving murder and theft cases.
Establishing paternity and maternity.
Identifying missing persons.
Identifying disaster victims.
Wildlife conservation and animal breeding.
Medical research and genetic disease studies.
Advantages
Extremely accurate and reliable.
Requires only a very small biological sample.
Can identify individuals even after many years.
Accepted as strong evidence in courts.
Limitations
Expensive equipment is required.
DNA samples may become contaminated.
Identical twins have almost identical DNA profiles, making differentiation difficult.
Simple Diagram of DNA Fingerprinting
Blood / Hair / Saliva
│
▼
DNA Extraction
│
▼
PCR Amplification
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│
▼
Gel Electrophoresis
│
▼
DNA Band Pattern (Fingerprint)
│
▼
Comparison with Another Sample
Easy Example
Think of a barcode on products in a supermarket. Every product has its own barcode that
identifies it. In the same way, every person has a unique DNA pattern that identifies them.
Conclusion
Both Transformation and DNA Fingerprinting are important concepts in genetics and
biotechnology.
Transformation is the process by which bacteria take up foreign DNA and acquire
new characteristics. It is a key tool in genetic engineering and biotechnology.
DNA Fingerprinting is a method used to identify individuals based on their unique
DNA patterns. It has become an essential tool in forensic science, medicine,
paternity testing, and biological research.
Understanding these concepts helps us appreciate how DNA influences heredity, scientific
discoveries, crime investigation, and the development of modern medical technologies.
This paper has been carefully prepared for educational purposes. If you notice any mistakes or
have suggestions, feel free to share your feedback.
