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GNDU Question Paper-2022

Ba/Bsc 5

Semester

ZOOLOGY : Paper-Zoo-V (A)

(Development Biology)

Time Allowed: Three Hours Maximum 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. Explain oogenesis and highlight role of follicles.

2. Write a note on the following:

(a) Polarity of egg

(b) Fertilization

SECTION-B

3. Describe cleavage and its patterns.

4. (a) Differentiate between determination and differentiation.

(b) What is an organizer ? Highlight its significance in embryonic development.

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SECTION-C

5. What is the fate of three germinal layers in chick?

6. Describe metamorphosis in frog.

SECTION-D

7. What are the types and functions of mammalian placenta ?

8. Write a note on:

(a) Regeneration

(b) Ageing and death.

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GNDU Answer Paper-2022

Ba/Bsc 5

Semester

ZOOLOGY : Paper-Zoo-V (B)

(Genetics)

Time Allowed: Three Hours Maximum 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) Pleiotropic genes

(b) Pseudoallelism.

Ans: (a) Pleiotropic Genes

Pleiotropy occurs when a single gene influences multiple phenotypic traits. This means that

one gene is responsible for affecting more than one aspect of an organism's physical or

physiological characteristics. Pleiotropic genes are crucial in understanding genetic

disorders, evolutionary biology, and the complexity of biological systems.

Types of Pleiotropy

1. Gene Pleiotropy: Refers to how many biochemical or functional traits are impacted

by a single gene. The gene affects various processes within the organism.

2. Developmental Pleiotropy: Involves mutations that impact multiple traits, which

might lead to conditions like deficiencies across different body systems.

3. Selectional Pleiotropy: Focuses on how gene mutations affect multiple aspects of an

organism’s fitness—its ability to survive and reproduce.

4. Antagonistic Pleiotropy: A gene mutation that offers a fitness advantage early in life

but can cause negative effects later, such as aging or disease susceptibility.

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Examples of Pleiotropic Genes:

1. Sickle Cell Anemia: A mutation in the HBB gene, which codes for the beta-globin

protein, causes red blood cells to become sickle-shaped. This gene mutation affects

not only the shape of blood cells but also results in organ damage (like the heart,

brain, and lungs), showing how pleiotropy can lead to complex health problems.

2. Phenylketonuria (PKU): This genetic disorder is caused by a mutation in the PAH

gene, which is responsible for breaking down the amino acid phenylalanine. A lack of

the enzyme leads to multiple issues, such as intellectual disabilities, skin

pigmentation changes, and developmental delays.

3. Frizzle Feather Trait in Chickens: This trait leads to curly feathers but also causes

additional effects like higher metabolism, larger organs, and delayed sexual maturity.

This is another classic example of how pleiotropy affects more than one trait.

Evolutionary Implications:

Pleiotropy is important for evolutionary biology as it shows how genes adapt to perform

multiple roles, contributing to an organism’s ability to survive in different environments. It

also shows how natural selection acts on genes, sometimes favoring mutations that have

both beneficial and harmful effects at different stages of life(

(b) Pseudoallelism

Pseudoallelism refers to a situation where two genes, although located very close to each

other on the same chromosome, appear to be alleles (alternative forms of the same gene)

because they affect the same phenotypic traits. However, these genes are distinct from

each other at the molecular level.

Characteristics of Pseudoalleles:

1. Close Linkage: Pseudoalleles are located so close to each other on the chromosome

that they are often inherited together, giving the appearance that they are alleles of

the same gene.

2. Functional Overlap: Although they are separate genes, pseudoalleles can affect the

same biological pathways or traits, leading to an impression that a single gene is

responsible for these traits.

3. Recombination: During genetic recombination, pseudoalleles can occasionally be

separated, which is how scientists can tell that they are, in fact, different genes,

despite their similar functions.

Example of Pseudoallelism:

An example of pseudoalleles can be found in the Drosophila melanogaster (fruit fly). The

genes responsible for eye color, white and apricot, are located so close to each other on the

X chromosome that they were once thought to be alleles. However, further research

showed that these are separate genes, despite their shared influence on eye pigmentation(

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Importance of Pseudoallelism:

Pseudoallelism has helped scientists understand how genes are organized on chromosomes

and how traits are inherited. It also provides insight into genetic mapping and the

relationships between closely linked genes, particularly in terms of how these genes might

be involved in similar physiological processes.

Conclusion

Both pleiotropic genes and pseudoallelism are key concepts in genetics that demonstrate

the complexity of gene functions and inheritance. Pleiotropy illustrates how one gene can

affect multiple traits, while pseudoallelism shows how separate genes located close to one

another can appear to influence the same trait. These mechanisms play vital roles in

understanding genetic disorders, evolutionary adaptations, and the intricacies of gene

regulation and expression

2. (a) What is the difference between linkage and crossing over?

(b) Write short note on sex linked characters.

Ans: (a) Difference Between Linkage and Crossing Over

Linkage:

• Definition: Linkage is the tendency of certain genes to be inherited together because

they are located close to each other on the same chromosome.

• How it Works: When genes are on the same chromosome, they are said to be

“linked.” This means they tend to stick together during the process of inheritance,

and are passed from parent to offspring as a group. Since chromosomes are

inherited as units (we get one set from each parent), linked genes often travel

together.

• Example: Imagine two genes, A and B, are located very close to each other on the

same chromosome. If your parents have these genes close together, there is a high

chance that you will inherit them together, without them getting separated.

• Key Point: Linkage occurs because chromosomes act like bundles of genes. The

closer two genes are to each other on a chromosome, the less likely it is for them to

be separated during reproduction.

Crossing Over:

• Definition: Crossing over is a process that happens during the formation of eggs and

sperm (in a process called meiosis). During this process, segments of homologous

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(similar) chromosomes can exchange pieces with each other. This exchange causes a

reshuffling of genes, which increases genetic diversity.

• How it Works: Crossing over occurs when chromosomes line up and exchange parts

of their genetic material. This mixing of genes can result in new combinations of

traits in offspring that were not present in the parents. Crossing over typically occurs

between genes that are far apart on a chromosome, and it helps break the linkage

between genes.

• Example: Let’s say genes A and B are on the same chromosome, but crossing over

occurs between them. This could result in gene A getting swapped with a gene from

a different chromosome, making gene A and B not be inherited together.

• Key Point: Crossing over happens to break the linkage between genes. It is a

mechanism that allows genes to be shuffled, which increases the variety of genetic

combinations in the offspring.

Differences Between Linkage and Crossing Over:

1. Definition:

o Linkage refers to genes being inherited together because they are on the

same chromosome.

o Crossing Over refers to the exchange of genetic material between

homologous chromosomes during meiosis, which leads to genetic

recombination.

2. Location on Chromosome:

o Linkage is more likely when genes are very close to each other on a

chromosome.

o Crossing Over is more likely to happen between genes that are far apart on

the chromosome.

3. Inheritance:

o Linkage tends to keep genes together, meaning they are inherited as a unit.

o Crossing Over separates linked genes, allowing for new combinations of

traits.

4. Genetic Diversity:

o Linkage reduces genetic diversity since linked genes are passed on together.

o Crossing Over increases genetic diversity by creating new gene combinations.

5. Frequency:

o Linkage is more common when genes are close together on a chromosome.

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o Crossing Over happens more frequently when genes are farther apart on the

chromosome.

(b) Sex-Linked Characters

What are Sex-Linked Characters?

• Definition: Sex-linked characters are traits that are determined by genes located on

the sex chromosomes (X and Y chromosomes). In most species, including humans,

sex is determined by two types of chromosomes: X and Y. Females typically have two

X chromosomes (XX), and males have one X and one Y chromosome (XY).

• How it Works: Since the X chromosome carries many more genes than the Y

chromosome, most sex-linked traits are associated with the X chromosome. A few

traits are carried on the Y chromosome, but these are rare and usually only affect

males.

Examples of Sex-Linked Characters:

1. Color Blindness:

o Color blindness is a common sex-linked trait, particularly the inability to

distinguish between red and green. This trait is carried on the X chromosome.

Since males only have one X chromosome, if they inherit the gene for color

blindness from their mother, they will be color blind. Females, on the other

hand, need to inherit two copies of the color blindness gene (one from each

parent) to express the trait.

2. Hemophilia:

o Hemophilia is a disorder where blood doesn’t clot properly. It is another

example of a sex-linked trait carried on the X chromosome. Similar to color

blindness, males are more likely to express this disorder because they only

have one X chromosome.

3. Duchenne Muscular Dystrophy (DMD):

o DMD is a genetic disorder that leads to muscle weakness and degeneration

over time. It is an X-linked recessive condition, meaning that males are far

more likely to suffer from it than females. Females can be carriers if they

inherit one faulty gene from one of their parents.

Types of Sex-Linked Traits:

• X-Linked Traits: These traits are associated with genes found on the X chromosome.

Since females have two X chromosomes and males have one, X-linked traits often

show different patterns of inheritance in males and females.

o For Males: Because males have only one X chromosome, a single copy of a

gene on the X chromosome can cause the trait to be expressed. This is why

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sex-linked traits like color blindness and hemophilia are more common in

males.

o For Females: Since females have two X chromosomes, they need to inherit

two copies of the gene (one from each parent) to express the trait. If they

only inherit one copy, they are usually carriers, meaning they do not show

symptoms of the trait but can pass it on to their children.

• Y-Linked Traits: These traits are passed from father to son because the Y

chromosome is only inherited by males. Y-linked traits are rare because the Y

chromosome contains fewer genes. An example of a Y-linked trait would be certain

conditions that affect male fertility.

Inheritance Patterns of Sex-Linked Traits:

1. X-Linked Recessive Inheritance:

o For a trait to be expressed in males, they only need to inherit one copy of the

gene from their mother. For females, they need to inherit two copies, one

from each parent. Examples include color blindness, hemophilia, and

Duchenne muscular dystrophy.

2. X-Linked Dominant Inheritance:

o In this case, only one copy of the gene is needed for the trait to be expressed

in both males and females. However, X-linked dominant disorders are much

rarer. An example is a condition called Rett syndrome.

3. Y-Linked Inheritance:

o These traits are passed from father to son through the Y chromosome. Since

females do not have a Y chromosome, they cannot inherit or pass on Y-linked

traits.

Importance of Sex-Linked Traits:

• Medical Importance: Many sex-linked traits, like hemophilia and muscular

dystrophy, have significant medical implications. Understanding how these traits are

passed on helps in genetic counseling and medical diagnosis.

• Evolutionary Significance: Sex-linked traits also play a role in evolution, particularly

in terms of genetic variation between males and females. In some cases, mutations

on the X chromosome can lead to differences in survival and reproduction between

the sexes.

Conclusion:

• Linkage and Crossing Over: These two concepts are crucial in understanding how

genes are inherited. Linkage tends to keep genes together on the same

chromosome, while crossing over separates them, promoting genetic diversity.

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• Sex-Linked Characters: Traits that are associated with the X and Y chromosomes,

particularly X-linked traits, follow unique patterns of inheritance. These traits are

important for understanding genetic diseases and inheritance patterns, especially

those that affect males and females differently.

Together, linkage, crossing over, and sex-linked traits form the foundation of how genetic

traits are passed down from generation to generation, shaping the diversity and inheritance

patterns we observe in living organisms.

SECTION-B

3. Explain the process of protein synthesis in prokaryotic cells.

Ans: Protein synthesis in prokaryotic cells is a complex but well-coordinated process where genetic

information is translated into functional proteins. It occurs in two major steps: transcription and

translation. Here’s a simplified and detailed explanation of the process, breaking down key elements

to make it easy to understand.

1. Transcription: Copying DNA to mRNA

The first step in protein synthesis is transcription, where a segment of DNA is copied into

messenger RNA (mRNA). In prokaryotes, this happens in the cytoplasm, as they do not have

a nucleus.

Steps of Transcription:

• Initiation: RNA polymerase, an enzyme, binds to a specific region of the DNA called

the promoter. This signals the DNA to unwind, and RNA polymerase can read one of

the DNA strands to start producing mRNA.

• Elongation: The RNA polymerase moves along the DNA, adding nucleotides to form a

single strand of mRNA. The nucleotides match the DNA template, but instead of

thymine (T), RNA uses uracil (U).

• Termination: When the RNA polymerase reaches a specific sequence of nucleotides

on the DNA (the terminator), the transcription process stops, and the mRNA strand

is released.

This mRNA strand is now ready to be used as a template for building proteins.

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2. Translation: From mRNA to Protein

Once transcription is complete, the mRNA carries the instructions to the ribosomes, which

are the cellular machinery responsible for synthesizing proteins. Prokaryotic ribosomes

consist of two subunits: 30S (small) and 50S (large), which together form a 70S ribosome.

a. Initiation

Translation begins with initiation, which involves several steps:

• The small ribosomal subunit (30S) binds to the mRNA. This attachment occurs near a

special sequence in the mRNA called the Shine-Dalgarno sequence, which helps align

the ribosome correctly.

• A special initiator tRNA carrying a modified amino acid called N-formylmethionine

(fMet) binds to the start codon (AUG) on the mRNA.

• The large ribosomal subunit (50S) joins the small subunit, forming a complete

ribosome. This creates the P site (where the initiator tRNA binds) and the A site

(where the next amino acid-carrying tRNA will bind).

b. Elongation

Once the initiation complex is formed, the process of elongation begins. This involves the

addition of amino acids to the growing protein chain.

• Aminoacyl-tRNA binding: The next tRNA, carrying the corresponding amino acid,

enters the A site of the ribosome and binds to the mRNA codon.

• Peptide bond formation: The ribosome catalyzes a reaction where the amino acid in

the P site is transferred to the amino acid in the A site, forming a peptide bond.

• Translocation: The ribosome moves along the mRNA, shifting the tRNAs. The tRNA

that was in the A site moves to the P site, and the tRNA in the P site moves to the E

site, where it is released. This movement continues down the mRNA strand.

This elongation process repeats for each codon along the mRNA, adding one amino acid at a

time to the growing polypeptide chain.

c. Termination

The process continues until the ribosome encounters one of the stop codons: UAA, UAG, or

UGA. Stop codons do not code for any amino acid, and no tRNA matches them.

• Release factors (RF-1, RF-2, and RF-3) bind to the stop codon and prompt the

ribosome to release the newly formed protein.

• The ribosome then disassembles, and the mRNA is released.

3. Post-Translation Modifications

In prokaryotes, post-translational modifications are relatively simple compared to

eukaryotes. These include folding the polypeptide chain into its final 3D structure and, in

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some cases, adding other molecules (like sugars or lipids) to the protein to make it

functional.

Key Components Involved

• mRNA (Messenger RNA): Carries the genetic code from DNA and serves as the

template for protein synthesis.

• tRNA (Transfer RNA): Carries specific amino acids to the ribosome. Each tRNA has an

anticodon that pairs with a corresponding codon on the mRNA.

• rRNA (Ribosomal RNA): A part of the ribosome's structure, it helps catalyze the

formation of peptide bonds.

Conclusion

Protein synthesis in prokaryotes is a vital process that enables the cell to translate genetic

information into functional proteins. The simplicity of prokaryotic cells, compared to

eukaryotic cells, allows for this process to occur efficiently, without the need for a nucleus

or complex post-transcriptional modifications. From the transcription of DNA to mRNA,

followed by the translation of mRNA into a polypeptide chain, this process is crucial for cell

function and survival.

4. Explain the following:

(a) Structure of DNA

(b) Wobble hypothesis.

Ans: (a) Structure of DNA (Deoxyribonucleic Acid)

Introduction to DNA

DNA, or deoxyribonucleic acid, is the molecule that carries the genetic instructions for the

growth, development, functioning, and reproduction of all living organisms and many

viruses. It's the blueprint for everything that happens in a cell, making it crucial for life.

Basic Components of DNA

DNA is composed of smaller building blocks known as nucleotides. Each nucleotide has

three parts:

1. Phosphate group: A group of atoms made up of phosphorus and oxygen. This is the

backbone of the DNA molecule.

2. Sugar (Deoxyribose): A five-carbon sugar that gives DNA its name (deoxyribo- refers

to this sugar).

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3. Nitrogenous base: This part varies, and there are four possible bases in DNA:

o Adenine (A)

o Thymine (T)

o Cytosine (C)

o Guanine (G)

The sugar and phosphate groups form the sides of the DNA "ladder," while the nitrogenous

bases pair up to form the rungs of the ladder. These bases pair in a specific way:

• Adenine (A) always pairs with Thymine (T) using two hydrogen bonds.

• Guanine (G) always pairs with Cytosine (C) using three hydrogen bonds.

These bonds between the bases hold the two strands of DNA together in a twisted structure

known as a double helix.

The Double Helix

James Watson and Francis Crick, with help from Rosalind Franklin's X-ray diffraction images,

discovered the double-helix structure of DNA in 1953. In this model, DNA looks like a

twisted ladder:

• The sugar and phosphate molecules form the "backbone" of the ladder.

• The base pairs (A-T and G-C) form the rungs.

The double helix structure is stabilized by hydrogen bonds between the base pairs. These

two strands of DNA run in opposite directions, which is referred to as antiparallel. One

strand runs from the 5' (five prime) to the 3' (three prime) direction, and the other runs

from 3' to 5'. This directionality is important for processes like DNA replication and protein

synthesis.

Functions of DNA

1. Storage of Genetic Information: DNA holds all the instructions for making the

proteins and molecules that are essential for life.

2. Replication: Before a cell divides, DNA replicates so that each new cell gets an exact

copy of the DNA.

3. Mutation and Evolution: Occasionally, the DNA sequence changes (mutates), which

can introduce new traits. Over time, these mutations are a key driver of evolution.

4. Gene Expression and Protein Synthesis: DNA codes for proteins, which are made

through processes called transcription and translation. These proteins do most of the

work in cells, acting as enzymes, structural components, and signaling molecules.

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DNA Replication

DNA replication is the process by which DNA makes an identical copy of itself during cell

division. The two strands of DNA unwind, and each serves as a template for the formation of

a new complementary strand. This process ensures that genetic information is passed on

accurately from one generation to the next.

1. Unwinding of the Double Helix: The enzyme helicase breaks the hydrogen bonds

between the base pairs, separating the two strands.

2. Complementary Base Pairing: Free nucleotides in the cell match up with their

complementary bases on each strand.

3. Formation of Two New DNA Molecules: The enzyme DNA polymerase helps to form

the new strands by adding nucleotides to the growing DNA chains.

Each new DNA molecule consists of one old strand and one new strand, which is why this

method of replication is called semi-conservative.

Genetic Code

The sequence of bases in DNA represents a code for making proteins. This genetic code is

read in triplets, called codons. Each codon consists of three bases and codes for one specific

amino acid (the building blocks of proteins). For example:

• The codon ATG codes for the amino acid methionine.

• The codon GGA codes for the amino acid glycine.

Proteins are synthesized by stringing together amino acids in the order specified by the

sequence of codons in DNA.

(b) Wobble Hypothesis

Introduction to the Genetic Code

The genetic code is the set of instructions in DNA that tells a cell how to make proteins.

Proteins are made up of long chains of amino acids, and the sequence of these amino acids

is determined by the sequence of codons in the DNA. There are 64 possible codons, but only

20 amino acids, so some amino acids are encoded by more than one codon.

The Role of tRNA in Protein Synthesis

Transfer RNA (tRNA) plays a key role in translating the genetic code from mRNA (messenger

RNA) into proteins. Each tRNA molecule has two important parts:

1. An anticodon: A set of three bases that are complementary to a codon on the mRNA

strand.

2. An amino acid attachment site: The tRNA carries a specific amino acid

corresponding to its anticodon.

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During protein synthesis, tRNA molecules bind to their corresponding codons on the mRNA

strand, bringing the correct amino acids to the growing protein chain.

The Problem: Codon-Anticodon Matching

There are 61 codons that specify amino acids (3 codons are "stop" codons that signal the

end of protein synthesis). Since there are 61 codons, we might expect that there would be

61 different tRNA molecules, one for each codon. However, there are fewer tRNA molecules

than codons, which raises a question: How can fewer tRNAs recognize more codons?

The Wobble Hypothesis: An Explanation

The Wobble Hypothesis, proposed by Francis Crick in 1966, explains how one tRNA can

recognize multiple codons. According to this hypothesis, the base pairing between the

codon and the anticodon follows the normal rules for the first two bases but is more flexible

(or "wobbles") at the third position.

• First two bases: These follow strict base-pairing rules (A pairs with U, and G pairs

with C in RNA).

• Third base: At the third position of the codon, non-standard base pairing can occur.

This flexibility allows one tRNA to pair with more than one codon. For example:

o A tRNA with the anticodon GCI (where "I" is inosine, a modified base) can pair

with three codons: GCA, GCC, and GCU, all of which code for the amino acid

alanine.

Implications of the Wobble Hypothesis

1. Efficiency: The wobble hypothesis allows the cell to use fewer tRNAs to cover all the

codons, making the process of protein synthesis more efficient.

2. Genetic Code Degeneracy: The genetic code is degenerate, meaning that multiple

codons can code for the same amino acid. The wobble hypothesis provides a

molecular explanation for this redundancy.

3. Flexibility in Mutation: The flexibility at the wobble position makes the genetic code

more robust to mutations. If a mutation changes the third base of a codon, it's more

likely that the codon will still code for the same amino acid, minimizing the impact of

the mutation.

Conclusion

In summary, DNA is the fundamental molecule that carries genetic information in all living

organisms. Its structure, the double helix, enables it to replicate and pass on genetic

information accurately. The wobble hypothesis provides a critical insight into how the

genetic code is read efficiently during protein synthesis, explaining why fewer tRNAs are

needed to recognize all possible codons. Both DNA structure and the wobble hypothesis

highlight the precision and flexibility of genetic processes that sustain life.

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SECTION-C

5. Write notes on the following:

(a) Detection of mutation in Drosophila

(b) Alaptonuria.

Ans: (a) Detection of Mutation in Drosophila

Drosophila melanogaster (fruit fly) has been a model organism in genetics due to its simple

genome and rapid reproduction. Detecting mutations in Drosophila involves several

methods, allowing geneticists to observe changes in physical traits or alterations in genetic

markers.

1. Phenotypic Observation: Mutations in Drosophila are often detected by observing

visible changes in traits such as eye color, wing shape, or body size. For example, a

change in eye color from red (wild type) to white indicates a mutation in the genes

responsible for pigment production.

2. Genetic Crosses: Another common method for mutation detection is through

controlled breeding experiments. By crossing Drosophila with known genotypes,

researchers can track how mutations are passed down through generations. If a

mutation is recessive, it may not be visible until crossed with another fly carrying the

same mutation.

3. Chromosomal Analysis: Researchers can also identify mutations by studying the

chromosomes of Drosophila under a microscope. Chromosomal rearrangements,

deletions, or duplications can be detected, often by using staining techniques that

highlight changes in chromosomal structure.

4. Molecular Techniques: Advanced methods, such as Polymerase Chain Reaction (PCR)

and DNA sequencing, are now used to detect mutations at the molecular level.

These techniques help identify point mutations (single nucleotide changes) or larger

structural changes within specific genes.

By using these techniques, scientists can study how mutations affect gene function, how

they are inherited, and their impact on Drosophila's phenotype. The ease of breeding and

observing fruit flies has made them invaluable for understanding the fundamentals of

genetics and mutation

(b) Alkaptonuria

Alkaptonuria is a rare genetic disorder caused by mutations in the HGD gene, which is

responsible for producing the enzyme homogentisate oxidase. This enzyme plays a key role

in breaking down certain amino acids, namely phenylalanine and tyrosine. When this

enzyme is defective or absent, a substance called homogentisic acid builds up in the body.

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1. Causes: Alkaptonuria results from mutations in both copies of the HGD gene,

inherited in an autosomal recessive manner. This means that both parents must

carry one copy of the mutated gene, though they typically do not show any

symptoms. The excess homogentisic acid is not properly processed and is instead

deposited in tissues like cartilage and skin.

2. Symptoms:

o Darkened Urine: One of the hallmark signs of alkaptonuria is that urine turns

dark when exposed to air. This is because the homogentisic acid in the urine

oxidizes and changes color.

o Ochronosis: Over time, the buildup of homogentisic acid leads to a condition

called ochronosis, where connective tissues darken. This affects the skin,

cartilage, and even ear and nose tips.

o Joint Problems: Individuals with alkaptonuria often develop arthritis,

particularly in the spine and large joints. This occurs because homogentisic

acid damages the cartilage, leading to degeneration over time.

3. Diagnosis: Diagnosis is typically made by observing the clinical symptoms and

confirming the presence of homogentisic acid in the urine. Genetic testing can also

be done to identify mutations in the HGD gene, providing a definitive diagnosis.

4. Treatment: There is no cure for alkaptonuria, but treatments aim to manage

symptoms. Patients are often advised to limit their intake of protein-rich foods, as

these contain phenylalanine and tyrosine. In severe cases, joint replacement

surgeries may be required due to arthritis. Researchers are exploring new

treatments, such as enzyme replacement therapy, which may help break down

homogentisic acid more effectively

In summary, both topics highlight important concepts in genetics. Detecting mutations in

Drosophila helps scientists understand genetic inheritance, while studying rare genetic

disorders like alkaptonuria offers insight into how genetic mutations impact human health.

6. Describe extranuclear inheritance with special reference to Mirabilis jalapa.

Ans: Extranuclear inheritance, also known as cytoplasmic inheritance, refers to the

transmission of genetic information through structures located outside the nucleus of a cell.

Unlike typical inheritance patterns that involve genes found on chromosomes within the

nucleus, extranuclear inheritance involves genes located in other parts of the cell, such as

the mitochondria and chloroplasts. These genes play a crucial role in various cellular

processes, but they follow a different pattern of inheritance compared to nuclear genes.

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One classic example of extranuclear inheritance is seen in the plant Mirabilis jalapa, also

known as the four o'clock plant.

Understanding the Basics of Extranuclear Inheritance

Before diving into the specific case of Mirabilis jalapa, it's important to understand the

foundational concepts of extranuclear inheritance:

1. Nuclear vs. Extranuclear Genes: In most organisms, the majority of genetic material

is housed in the nucleus. These genes follow the laws of Mendelian inheritance,

where traits are passed down through alleles on chromosomes from both parents.

Extranuclear genes, on the other hand, are found in the cytoplasmic organelles, such

as mitochondria (in both animals and plants) and chloroplasts (in plants). These

genes are inherited independently of the nuclear genes.

2. Mitochondrial DNA: Mitochondria are known as the powerhouses of the cell

because they produce energy. They have their own small set of DNA, separate from

the nuclear DNA. In most organisms, mitochondrial DNA is inherited maternally,

meaning it is passed down from the mother to her offspring.

3. Chloroplast DNA: Chloroplasts are the organelles responsible for photosynthesis in

plants. Like mitochondria, chloroplasts have their own DNA, which is also inherited in

a non-Mendelian fashion. Chloroplast inheritance can be either maternal, paternal,

or biparental, depending on the species.

4. Non-Mendelian Inheritance: Since extranuclear genes are not located on

chromosomes in the nucleus, they do not follow Mendel's laws of segregation and

independent assortment. Instead, their inheritance is often uniparental, meaning

they are passed down from only one parent, usually the mother.

Extranuclear Inheritance in Mirabilis jalapa

One of the most well-known examples of extranuclear inheritance is found in Mirabilis

jalapa, a flowering plant commonly known as the four o'clock plant. This plant is famous for

its unique inheritance pattern of leaf color, which does not follow the traditional Mendelian

rules of inheritance.

Observations in Mirabilis jalapa Leaf Color

In Mirabilis jalapa, the leaves can exhibit different colors, typically green, white, or

variegated (a mixture of green and white). This color variation is determined by the

chloroplasts, which are the organelles responsible for photosynthesis in plant cells.

The three common phenotypes of Mirabilis jalapa leaves are:

• Green leaves: These contain normal, functioning chloroplasts that produce

chlorophyll, the green pigment necessary for photosynthesis.

• White leaves: These lack functional chloroplasts and therefore do not produce

chlorophyll, giving the leaves a white appearance.

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• Variegated leaves: These have a mix of green and white sectors, indicating a mixture

of normal and defective chloroplasts within the same plant.

The Experiment

The key experiment that revealed the extranuclear inheritance of leaf color in Mirabilis

jalapa was conducted by Carl Correns in 1909. He crossed plants with different leaf colors

and observed the inheritance patterns of the offspring. Unlike Mendelian traits, where the

offspring's traits are determined by the combination of alleles inherited from both parents,

Correns found that the leaf color in Mirabilis jalapa was determined solely by the maternal

parent.

For example:

• When a plant with green leaves (maternal parent) was crossed with a plant with

white leaves (paternal parent), all the offspring had green leaves.

• When a plant with white leaves (maternal parent) was crossed with a plant with

green leaves (paternal parent), all the offspring had white leaves.

• When a variegated plant was used as the maternal parent, the offspring exhibited a

variety of leaf colors: green, white, or variegated.

These results clearly showed that the inheritance of leaf color in Mirabilis jalapa was

determined by the chloroplasts, which are passed down through the cytoplasm of the egg

cell (the maternal parent). Since the egg cell contributes most of the cytoplasm to the

offspring, it also determines the type of chloroplasts that the offspring will inherit.

The Role of Chloroplasts

Chloroplasts are organelles in plant cells that contain their own DNA. This DNA is separate

from the DNA found in the nucleus and is responsible for encoding proteins necessary for

photosynthesis and other functions within the chloroplast.

In the case of Mirabilis jalapa, the color of the leaves is determined by the functionality of

the chloroplasts:

• Green leaves contain functional chloroplasts that produce chlorophyll, allowing the

plant to perform photosynthesis and appear green.

• White leaves contain defective chloroplasts that cannot produce chlorophyll,

resulting in the absence of green pigment and giving the leaves a white appearance.

• Variegated leaves have a mixture of both functional and defective chloroplasts,

leading to a combination of green and white sectors on the same leaf.

Since chloroplasts are inherited maternally in Mirabilis jalapa, the leaf color of the offspring

is determined solely by the type of chloroplasts present in the egg cell of the mother.

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Non-Mendelian Inheritance in Mirabilis jalapa

The inheritance pattern observed in Mirabilis jalapa does not follow Mendel's laws of

inheritance because it is controlled by genes located in the chloroplasts rather than in the

nucleus. Mendelian inheritance involves the segregation of alleles during the formation of

gametes, with each parent contributing one allele for each trait. In the case of extranuclear

inheritance, however, the traits are determined by the genes in the cytoplasmic organelles,

which are typically inherited from only one parent.

In Mirabilis jalapa, the leaf color is inherited maternally because the egg cell provides most

of the cytoplasm (and therefore the chloroplasts) to the offspring. The pollen (sperm cell)

contributes very little cytoplasm, so the chloroplasts from the paternal parent do not

influence the leaf color of the offspring.

Significance of Extranuclear Inheritance

Extranuclear inheritance plays a crucial role in the evolution and development of many

organisms. While nuclear genes control the majority of traits, extranuclear genes, such as

those found in mitochondria and chloroplasts, are essential for certain cellular functions.

Understanding extranuclear inheritance is important for several reasons:

1. Cellular Function: Mitochondria and chloroplasts are essential for energy production

in cells. Mitochondria generate ATP through cellular respiration, while chloroplasts

perform photosynthesis in plants. Defects in the DNA of these organelles can lead to

diseases or abnormal traits, as seen in Mirabilis jalapa.

2. Maternal Inheritance: Many traits controlled by extranuclear genes are inherited

maternally. This is because the egg cell contributes most of the cytoplasm to the

offspring, including the mitochondria and chloroplasts. This pattern of inheritance is

observed not only in plants like Mirabilis jalapa but also in animals, where

mitochondrial DNA is passed down from the mother.

3. Evolutionary Implications: Extranuclear inheritance adds another layer of

complexity to the study of genetics and evolution. Since extranuclear genes are

inherited independently of nuclear genes, they can evolve and change in different

ways. This can lead to unique evolutionary adaptations, particularly in energy-

producing organelles like mitochondria and chloroplasts.

4. Genetic Disorders: In humans and other animals, mutations in mitochondrial DNA

can lead to a variety of genetic disorders, including mitochondrial myopathy, Leber's

hereditary optic neuropathy, and others. These disorders are inherited maternally,

similar to the way leaf color is inherited in Mirabilis jalapa.

5. Plant Breeding: Understanding extranuclear inheritance is important in plant

breeding, especially when it comes to traits related to photosynthesis and

chloroplast function. By studying the inheritance patterns of chloroplast genes, plant

breeders can develop new varieties with improved traits, such as better

photosynthetic efficiency or resistance to environmental stress.

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Conclusion

Extranuclear inheritance, as demonstrated by the classic example of Mirabilis jalapa,

highlights the complexity of genetic inheritance beyond the nuclear genome. In the case of

Mirabilis jalapa, the maternal inheritance of chloroplasts determines the leaf color of the

offspring, following a pattern of inheritance that deviates from Mendel's laws. The study of

extranuclear inheritance is essential for understanding the role of cytoplasmic organelles in

cellular function, evolution, and genetic disorders. This concept is not only important in

plants like Mirabilis jalapa but also in animals and humans, where extranuclear genes play a

crucial role in energy production and disease inheritance.

SECTION-D

7. Discuss in detail about Hardy-Weinberg Law.

Ans: The Hardy-Weinberg Law is a fundamental principle in genetics that explains how allele

and genotype frequencies in a population remain constant from generation to generation,

provided that certain assumptions are met. This is referred to as genetic equilibrium. The

law was independently formulated by mathematician Godfrey Harold Hardy and physician

Wilhelm Weinberg in 1908.

Understanding the Hardy-Weinberg Principle:

In simple terms, the Hardy-Weinberg principle states that the genetic variation in a

population will remain the same over time unless specific forces act to change it. These

forces include mutations, natural selection, gene flow (migration), genetic drift (random

changes), and non-random mating.

To understand this better, let's consider a gene with two alleles: A (dominant) and a

(recessive). According to the Hardy-Weinberg equation, the frequency of these alleles in a

large population that is not evolving (i.e., is in equilibrium) can be represented as:

p + q = 1

Where:

• p is the frequency of the dominant allele (A)

• q is the frequency of the recessive allele (a)

If we look at the genotypes of the individuals in the population, the frequencies of the

possible genotypes (AA, Aa, and aa) can be represented by the equation:

p² + 2pq + q² = 1

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Here:

• p² represents the frequency of individuals with the homozygous dominant genotype

(AA)

• 2pq represents the frequency of individuals with the heterozygous genotype (Aa)

• q² represents the frequency of individuals with the homozygous recessive genotype

(aa)

Key Assumptions of the Hardy-Weinberg Law:

For a population to remain in Hardy-Weinberg equilibrium, five conditions must be met:

1. No mutations: The genetic code must remain unchanged.

2. Random mating: Every individual must have an equal chance to mate with any

other.

3. No natural selection: All genotypes must have equal chances of survival and

reproduction.

4. Large population size: The population must be large enough to prevent random

genetic drift.

5. No gene flow: No new alleles can be added or lost through migration.

When these conditions are met, the allele and genotype frequencies in the population will

remain constant across generations. If any of these assumptions are violated, the

population will not be in equilibrium, and the genetic frequencies will change, indicating

that evolution is occurring.

Practical Applications of the Hardy-Weinberg Principle:

The Hardy-Weinberg Law is crucial for understanding real-world genetics, particularly in

fields like evolutionary biology and population genetics. It helps scientists:

1. Determine if a population is evolving: By comparing observed genetic frequencies

with expected ones, scientists can determine whether evolution is happening in a

population. Any significant deviations suggest evolutionary forces at play.

2. Calculate carrier frequencies for genetic diseases: The principle is used to estimate

the number of carriers of recessive genetic disorders, such as cystic fibrosis or sickle

cell anemia. For instance, if a population has a known frequency of individuals with a

recessive disease, the Hardy-Weinberg equation can be used to estimate how many

individuals are heterozygous carriers of the disease gene.

3. Understand allele frequencies: It helps in calculating the frequency of different

alleles in populations, which is essential for understanding genetic diversity and

population structure.

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Example of Hardy-Weinberg in Action:

Consider a population where the recessive allele causes a genetic disorder, and 1 in 10,000

people exhibit this disorder. Using the Hardy-Weinberg equation, we can determine the

frequency of the carrier (heterozygous) individuals.

Let the recessive allele frequency (q²) be 1/10,000 = 0.0001. To find q, we take the square

root:

q = √0.0001 = 0.01

Now, since p + q = 1, we can calculate p:

p = 1 - q = 1 - 0.01 = 0.99

Using the formula for heterozygous individuals (2pq):

2pq = 2 × 0.99 × 0.01 = 0.0198

Thus, about 1.98% of the population are carriers of the recessive allele.

Factors that Disrupt Hardy-Weinberg Equilibrium:

1. Mutations: Mutations introduce new alleles into a population, altering the allele

frequencies and potentially causing evolution.

2. Natural Selection: If certain genotypes have an advantage in survival and

reproduction, the allele frequencies will shift.

3. Gene Flow: Migration introduces or removes alleles, changing the genetic structure

of the population.

4. Genetic Drift: In small populations, random changes in allele frequencies can occur,

especially after a population bottleneck or founder event.

5. Non-random Mating: If individuals mate preferentially, certain alleles may increase

in frequency, violating the assumption of random mating.

Importance of Hardy-Weinberg Law in Genetics:

The Hardy-Weinberg principle plays a crucial role in population genetics, serving as a

baseline for measuring genetic variation. If observed frequencies deviate from those

expected under Hardy-Weinberg equilibrium, it indicates that evolutionary forces are acting

on the population. It also helps in understanding the spread of genetic diseases and in

predicting how certain traits will be passed on in future generations.

In conclusion, the Hardy-Weinberg Law provides a critical framework for understanding the

genetic composition of populations. It shows that allele and genotype frequencies will

remain stable over time in the absence of evolutionary pressures. However, when these

conditions are not met, changes in genetic variation can be observed, which helps scientists

study evolution, genetic disorders, and the genetic diversity of populations(

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8. Write short notes on:

(a) Conjugation

(b) DNA fingerprinting

Ans: (a) Conjugation

Conjugation is a process that occurs in some bacteria and is sometimes called "bacterial

sex." But don't worry - it's not as scandalous as it sounds! Let's break it down:

What is conjugation? Conjugation is a way for bacteria to share genetic material (DNA) with

each other. It's like bacteria giving each other little gifts of genes. This process helps bacteria

adapt and survive in changing environments.

How does conjugation work?

1. The giver and the receiver:

o One bacterium acts as the "donor" (the giver)

o Another bacterium acts as the "recipient" (the receiver)

2. Making a connection:

o The donor bacterium grows a special tube called a pilus

o This pilus reaches out and attaches to the recipient bacterium

o Think of it like a tiny bridge between the two bacteria

3. Sharing DNA:

o The donor sends a copy of some of its DNA through the pilus

o This DNA is usually in the form of a plasmid (a small, circular piece of DNA)

o The recipient takes in this new DNA

4. Using the new genes:

o The recipient can now use the genes it received

o This might give it new abilities, like resistance to antibiotics

Why is conjugation important?

1. Spreading helpful traits:

o Bacteria can share genes that help them survive

o For example, genes for antibiotic resistance can spread quickly

2. Adapting to new environments:

o Bacteria can gain new abilities without having to evolve them on their own

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o This helps them adjust to changes in their surroundings

3. Genetic diversity:

o Conjugation mixes up bacterial genes

o This creates more variety in bacterial populations

4. Medical concerns:

o Conjugation can make it harder to treat bacterial infections

o Doctors and scientists need to understand this process to develop better

treatments

Examples of conjugation in action:

1. Antibiotic resistance:

o One bacterium develops resistance to an antibiotic

o Through conjugation, it can share this resistance with other bacteria

o This makes infections harder to treat

2. Gaining new abilities:

o Some bacteria can't break down certain food sources

o Through conjugation, they might receive genes that allow them to use new

food types

3. Cleaning up pollution:

o Some bacteria can break down harmful chemicals

o They could share these genes with other bacteria, helping to clean up

polluted areas

Interesting facts about conjugation:

1. Not all bacteria can do it:

o Only some types of bacteria are able to perform conjugation

o Those that can are called "fertility factor positive" or F+ bacteria

2. It's not just for bacteria:

o Some other single-celled organisms, like certain algae, can also do

conjugation

3. It's different from reproduction:

o Conjugation doesn't create new bacteria

o It just allows existing bacteria to share genetic material

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4. Scientists use it in research:

o Conjugation is a useful tool for genetic engineering

o Researchers can use it to introduce new genes into bacteria for study or to

produce useful substances

5. It can happen between different species:

o Conjugation isn't limited to bacteria of the same type

o This allows for even more genetic mixing and adaptation

In summary, conjugation is a fascinating process that allows bacteria to share genetic

material. It's like a microbial gift exchange of genes, helping bacteria adapt and survive in

changing environments. This process plays a crucial role in the spread of antibiotic

resistance and the evolution of bacterial populations.

(b) DNA Fingerprinting

Now, let's explore DNA fingerprinting, which is like creating a unique genetic ID card for

living things. It's a powerful tool used in forensics, medicine, and research.

What is DNA fingerprinting? DNA fingerprinting is a method used to identify and compare

the genetic makeup of different individuals. It's based on the fact that every person (except

identical twins) has a unique DNA sequence.

How does DNA fingerprinting work?

1. Getting a DNA sample:

o This can come from blood, saliva, hair, or other biological materials

o Only a tiny amount is needed

2. Extracting the DNA:

o Scientists use special chemicals to separate the DNA from other cell

components

3. Cutting the DNA:

o Enzymes called "restriction enzymes" cut the DNA at specific points

o This creates fragments of different lengths

4. Separating the fragments:

o The DNA fragments are placed in a special gel

o An electric current is applied, causing the fragments to move

o Smaller fragments move faster than larger ones

o This creates a pattern of bands, like a barcode

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5. Transferring the pattern:

o The pattern is transferred to a special membrane

6. Adding probes:

o Scientists add radioactive or fluorescent "probes"

o These attach to specific DNA sequences

7. Creating the fingerprint:

o The final result looks like a series of dark bands

o This pattern is unique to each individual

8. Comparing fingerprints:

o Scientists can compare fingerprints from different samples

o This helps determine if they came from the same person or are related

Why is DNA fingerprinting important?

1. Solving crimes:

o It can link suspects to crime scenes

o It can also exonerate innocent people

2. Identifying victims:

o Useful in disasters or when bodies are difficult to identify

3. Determining family relationships:

o Can prove or disprove paternity

o Helpful in inheritance disputes

4. Wildlife conservation:

o Tracking endangered species

o Identifying illegally traded animal products

5. Agricultural applications:

o Improving crop breeding

o Protecting plant varieties

6. Medical research:

o Studying genetic diseases

o Developing personalized treatments

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Examples of DNA fingerprinting in action:

1. Criminal investigations:

o The first use of DNA fingerprinting in a criminal case was in 1986 in the UK

o It helped solve a double murder case and exonerated an innocent suspect

2. Identifying victims of disasters:

o DNA fingerprinting was used to identify victims of the 9/11 attacks

o It's also used in natural disasters like tsunamis or earthquakes

3. Reuniting families:

o It has helped reunite families separated by war or political conflicts

4. Protecting endangered species:

o DNA fingerprinting is used to track populations of rare animals

o It helps identify poached animal products

5. Food safety:

o It can be used to trace the origin of food products

o This helps in cases of contamination or fraud

Interesting facts about DNA fingerprinting:

1. It was discovered by accident:

o In 1984, scientist Alec Jeffreys was studying hereditary diseases

o He noticed that certain DNA sequences were unique to individuals

2. It's not just for humans:

o DNA fingerprinting can be used on any living organism

o It's even used to identify different strains of bacteria or viruses

3. It doesn't use actual fingerprints:

o Despite the name, it doesn't involve physical fingerprints

o The "fingerprint" is a metaphor for the unique genetic pattern

4. Identical twins have the same DNA fingerprint:

o This is because they come from the same fertilized egg

o However, new techniques are being developed to tell them apart

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5. It's getting faster and cheaper:

o Early DNA fingerprinting took weeks and was very expensive

o Now it can be done in hours and is much more affordable

6. There are ethical concerns:

o Some worry about privacy issues with DNA databases

o There are debates about when and how DNA fingerprinting should be used

How DNA fingerprinting has evolved:

1. Early days:

o The original technique used radioactive probes

o It required large amounts of DNA and took weeks to complete

2. PCR revolution:

o The development of Polymerase Chain Reaction (PCR) in the 1980s was a

game-changer

o PCR allows scientists to make many copies of a small DNA sample

o This made DNA fingerprinting possible with tiny amounts of DNA

3. STR analysis:

o Short Tandem Repeat (STR) analysis is now the most common method

o It's faster and more accurate than earlier techniques

4. Next-generation sequencing:

o New DNA sequencing technologies are making fingerprinting even more

powerful

o They can provide more detailed genetic information

5. Portable devices:

o Scientists are developing handheld DNA fingerprinting devices

o These could allow for rapid testing in the field

Limitations and challenges:

1. Contamination:

o DNA samples can be easily contaminated, leading to false results

o Strict protocols are needed to prevent this

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2. Interpretation:

o Reading DNA fingerprints requires skill and experience

o Mistakes can have serious consequences in criminal cases

3. Partial samples:

o Sometimes only partial DNA fingerprints can be obtained

o This can make identification less certain

4. Privacy concerns:

o There are debates about who should have access to DNA databases

o Some worry about genetic information being misused

5. Cost:

o While cheaper than before, DNA fingerprinting is still expensive for many

applications

In conclusion, DNA fingerprinting is a powerful technique that has revolutionized many

fields, from criminal justice to conservation. It allows us to identify individuals and

relationships with incredible accuracy, based on the unique genetic code we all carry. As

technology continues to advance, DNA fingerprinting is becoming faster, cheaper, and more

accessible, opening up new possibilities for its use in science, medicine, and society.

Both conjugation in bacteria and DNA fingerprinting demonstrate the incredible complexity

and importance of DNA in living organisms. While conjugation shows how genetic material

can be shared between bacteria, DNA fingerprinting reveals how the uniqueness of each

individual's genetic code can be used for identification. These processes highlight the power

of genetics in shaping life and our understanding of it.

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