RBSE Solutions Class 12 Biology Chapter 37 Mutations

RBSE Class 12 Biology Chapter 37 Multiple Choice Questions

Question 1. What is a Genome?
(a) Sum total of a haploid set of chromosome & extra chromosomal material of the cell
(b) Total No. of a chromosome is an organism
(c) diploid sets of chromosomes
(d) number of chromosomes found in the zygote
Answer: (a) Sum total of a haploid set of chromosome & extra chromosomal material of the cell
In simple words: A genome includes all the genetic material in an organism, specifically all the DNA found in a haploid set of chromosomes, plus any extra DNA outside the chromosomes within the cell. It's like a complete instruction manual for that organism.

🎯 Exam Tip: Remember that a genome includes not only chromosomal DNA but also extrachromosomal genetic material, which is a key distinguishing feature for full marks.

Question 2. How many numbers of nucleotides pairs found in human?
(a) \( 3.1647 \times 10^9 \)
(b) \( 3.1647 \times 10^7 \)
(c) \( 3.1647 \times 10^5 \)
(d) \( 3.1647 \times 10^3 \)
Answer: (a) \( 3.1647 \times 10^9 \)
In simple words: Humans have about 3.16 billion pairs of nucleotides in their genetic code. These pairs are the building blocks of DNA, holding all the information that makes us who we are.

🎯 Exam Tip: It is helpful to remember the approximate number of nucleotide base pairs in the human genome, as this is a fundamental piece of information in genetics.

Question 3. What is the basis of DNA fingerprinting?
(a) Self copy of DNA
(b) Fingerprint of DNA
(c) DNA fingerprints of two individual are not the same
(d) none of the options
Answer: (c) DNA fingerprints of two individual are not the same
In simple words: DNA fingerprinting works because every person (except identical twins) has a unique pattern of DNA. This makes it a powerful tool for identifying individuals.

🎯 Exam Tip: The uniqueness of an individual's DNA profile (excluding identical twins) is the core principle that makes DNA fingerprinting effective for identification.

Question 4. Dolly was produced by the help of which technique:
(a) From normal hybridization
(b) From normal sexual reproduction
(c) From cloning
(d) From Tissue Culture
Answer: (c) From cloning
In simple words: Dolly the sheep was the first mammal created using a special method called cloning. This means she was an exact genetic copy of an adult sheep, not made through natural breeding.

🎯 Exam Tip: Dolly the sheep is a classic example in biology; remember that her creation was a landmark achievement in reproductive cloning, not a result of traditional breeding methods.

Question 5. What is a Mutation?
(a) Change in the genetic material of DNA
(b) Permanent and Hereditary change in the DNA
(c) Change in the cytoplasm of the cell
(d) any kind of variations
Answer: (b) Permanent and Hereditary change in the DNA
In simple words: A mutation is a change in the DNA that is permanent and can be passed down from parents to children. It's a key source of genetic variation in living things.

🎯 Exam Tip: The two essential characteristics of a mutation are that it is permanent and heritable, meaning it can be passed on to future generations.

Question 6. If adenine is replaced from guanine than mutation is -
(a) Frameshift mutation
(b) Transversion
(c) Transition
(d) Translocation
Answer: (b) Transversion
In simple words: When a purine base like adenine is swapped for a pyrimidine base like guanine, this type of genetic change is called a transversion mutation. It's a specific kind of point mutation in DNA.

🎯 Exam Tip: Distinguish between transition (purine to purine or pyrimidine to pyrimidine) and transversion (purine to pyrimidine or vice versa) mutations for questions involving base substitutions.

Question 7. Genetic code includes
(a) 3 nucleotide bases, 64 codons
(b) 3 nucleotide bases, 18 codons
(c) 2 bases, 32 codons
(d) 2 bases, 64 codons
Answer: (a) 3 nucleotide bases, 64 codons
In simple words: The genetic code uses groups of three nucleotide bases, called codons, to specify amino acids. There are 64 possible codons, which are enough to code for all the amino acids needed for proteins.

🎯 Exam Tip: Remember that each codon consists of three nucleotide bases, and there are 64 possible combinations, though only 20 amino acids are coded by these.

Question 8. Polyploidy can be produced by -
(a) Colchicines
(b) X rays
(c) Gamma Rays
(d) None of the options
Answer: (a) Colchicines
In simple words: Colchicine is a chemical often used in biology to make cells have more than two complete sets of chromosomes, a condition known as polyploidy. It works by stopping cell division at a certain stage.

🎯 Exam Tip: Colchicine is a classic example of a chemical agent that induces polyploidy by interfering with spindle fiber formation during cell division.

RBSE Class 12 Biology Chapter 37 Very Short Answer Type Questions

Question 1. Human Genome Project was started by which international Agencies.
Answer: The Human Genome Project was started by the National Institute of Health and the Department of Energy in America. This large-scale effort aimed to map the entire human genome.
In simple words: Two main groups from America, the National Institute of Health and the Department of Energy, began the Human Genome Project.

🎯 Exam Tip: When listing agencies for major scientific projects, mention both names correctly to show complete knowledge.

Question 2. What are VNTRs?
Answer: VNTRs, which stands for Variable Number of Tandem Repeats, are small sections of DNA made of nucleotides that repeat many times. These repeating segments vary in length among different individuals, making them useful for DNA fingerprinting.
In simple words: VNTRs are short parts of DNA that repeat over and over, and the number of times they repeat is different for each person.

🎯 Exam Tip: Focus on explaining both what VNTRs are (repeating nucleotide segments) and their key characteristic (variable number of repeats) for a full definition.

Question 3. The addition of one or more complete sets of chromosomes numbers occurs is called?
Answer: The addition of one or more complete sets of chromosomes is called Euploidy. This condition means an organism has extra full sets of chromosomes, such as having three sets instead of the usual two. This is distinct from aneuploidy, which involves changes in individual chromosome numbers.
In simple words: When a cell gets one or more extra full sets of chromosomes, it is called euploidy.

🎯 Exam Tip: Clearly differentiate euploidy (changes in complete sets of chromosomes) from aneuploidy (changes in individual chromosome numbers) to avoid common mistakes.

Question 4. What is Non-disjunction?
Answer: Non-disjunction is when chromosomes fail to separate correctly during cell division. This can happen in two ways: either a pair of homologous chromosomes does not separate in meiosis-I, or sister chromatids do not separate during meiosis-II. This failure leads to cells receiving an abnormal number of chromosomes.
In simple words: Non-disjunction means chromosomes do not split apart properly during cell division, leading to an uneven number of chromosomes in new cells.

🎯 Exam Tip: When defining non-disjunction, specify both possible stages where it can occur (meiosis-I and meiosis-II) for a comprehensive answer.

Question 5. What are mutagens?
Answer: Mutagens are agents that can cause changes in the genetic material of an organism, leading to mutations. These factors can be physical, chemical, or biological and can alter DNA sequences or chromosome structure. UV radiation is an example of a physical mutagen.
In simple words: Mutagens are things that cause changes in DNA.

🎯 Exam Tip: Remember that mutagens include physical, chemical, and biological agents, all of which have the potential to induce genetic mutations.

Question 6. Define Probe.
Answer: A probe in molecular biology is a short piece of DNA or RNA that has a known sequence. It is often labeled with a radioactive or fluorescent tag so it can be easily detected. Probes are used to find specific DNA or RNA sequences in a sample by binding to them.
In simple words: A probe is a labeled DNA or RNA piece that finds and sticks to specific genetic sequences.

🎯 Exam Tip: Emphasize that a probe is a labeled (radioactive or fluorescent) fragment of DNA or RNA used to detect specific complementary sequences.

Question 7. What is the Honolulu Technique? Who developed this technique and where.
Answer: The Honolulu Technique is a method used to produce animal clones. It was developed by Teruhiko Wakayama and Ryuzo Yanagimachi at the University of Hawaii in 1998. This technique refined somatic cell nuclear transfer for more efficient cloning.
In simple words: The Honolulu Technique is a cloning method for animals, created by Teruhiko Wakayama and Ryuzo Yanagimachi at the University of Hawaii in 1998.

🎯 Exam Tip: For historical questions, ensure you include the developers, their institution, and the year for a complete answer.

RBSE Class 12 Biology Chapter 37 Short Answer Type Questions

Question 1. Define Gene Mutation.
Answer: A gene mutation occurs when there is a mismatch combination of nitrogenous bases in the newly formed daughter DNA. If this specific change happens at the level of a single gene, it is known as a Gene Mutation. These small changes can affect protein production.
In simple words: A gene mutation is a mistake in the DNA's building blocks (nitrogenous bases) that happens in one specific gene.

🎯 Exam Tip: Define gene mutation by highlighting that it's a change at the gene level, often involving base mismatches during DNA replication.

Question 3. Define point mutation.
Answer: A point mutation is a type of gene mutation where a single nucleotide base is changed, inserted, or deleted in the DNA sequence. This change happens at a specific location on the chromosomes, which is why it is also known as a Point mutation. These small changes can have a big effect on proteins.
In simple words: A point mutation is a small change in just one DNA building block at a specific spot on a chromosome.

🎯 Exam Tip: Emphasize that a point mutation involves an alteration at a single nucleotide base pair to distinguish it from larger chromosomal mutations.

Question 4. Define genome.
Answer:
Genome:
• A genome is the complete set of genetic instructions in an organism, stored in its DNA (or RNA for some viruses). It is like an instruction book for life. For humans, the Human Genome Project aimed to map and sequence this entire genetic blueprint.
• Genes are crucial parts of the genome that determine our traits and how our bodies function, and they also hold clues about our past and future.
• The DNA sequence can vary between individuals at specific locations, which scientists study to fully map and understand the human genome.
• In simple terms, the haploid set of chromosomes found in a cell is also considered a genome, representing one complete set of genetic material.
In simple words: A genome is all the genetic information (DNA) found in an organism. It contains the complete set of instructions for building and operating that organism.

🎯 Exam Tip: Remember that the genome includes all genetic material, not just genes, and that the haploid set of chromosomes in a cell represents its genome.

Question 5. What is Euploidy?
Answer:
Euploidy or Polyploidy:
The total number of chromosomes in a cell or organism is called monoploidy if it's a single set. Euploidy refers to the condition where an organism gains one or more complete sets of chromosomes. This means instead of the normal two sets (diploid), an organism might have three, four, or more complete sets. This condition can be of two main types:
• Autopolyploidy: This occurs when an organism has multiple sets of chromosomes derived from a single species.
• Allopolyploidy: This happens when an organism has multiple sets of chromosomes derived from two or more different species.
In simple words: Euploidy is when an organism has extra full sets of chromosomes beyond the usual number.

🎯 Exam Tip: Distinguish between euploidy (variation in entire sets of chromosomes) and aneuploidy (variation in individual chromosome numbers) and remember the two main types of euploidy, autopolyploidy and allopolyploidy.

Question 6. What is a silent mutation?
Answer: A silent mutation is a type of point mutation in DNA that does not cause a change in the amino acid sequence of the protein. Even though the nucleotide sequence changes, the resulting codon still codes for the same amino acid, or a functionally equivalent one. This happens due to the redundancy of the genetic code, where multiple codons can specify the same amino acid. This type of mutation often goes unnoticed because the protein function remains normal.
In simple words: A silent mutation changes the DNA but does not change the protein that is made from it.

🎯 Exam Tip: The key feature of a silent mutation is that despite a change in the DNA, the resulting amino acid sequence (and thus protein function) remains unaffected due to the degeneracy of the genetic code.

Question 7. What is gene cloning?
Answer:
Gene Cloning:
• Gene cloning is the process of creating many identical copies of a specific DNA fragment in a pure form. This process allows scientists to study individual genes in detail.
• It involves creating recombinant DNA by joining a DNA fragment (passenger DNA) from one organism with another DNA molecule (vehicle DNA), typically from a bacterial cell.
• This combined DNA is then introduced into a host cell, usually a bacterium, where it can replicate and produce many copies as the host cell divides.
• This process is a core part of genetic engineering, enabling the transfer and multiplication of desired genes across organisms.
• The recombinant DNA is made by cutting both the passenger and vehicle DNA with the same restriction enzymes, creating complementary sticky ends. These ends then join together and are sealed by an enzyme called ligase.
• Once the recombinant DNA is inside host bacteria, they take it up along with nutrients.
• As the bacteria grow and divide, the recombinant DNA also replicates, producing a large collection of identical DNA fragments, known as a clone.
In simple words: Gene cloning is making many exact copies of a specific piece of DNA by putting it into a host cell, like bacteria, and letting it multiply.

🎯 Exam Tip: When explaining gene cloning, be sure to include the roles of recombinant DNA, restriction enzymes, ligase, and a host organism for a complete understanding.

Question 8. Define Wobble Hypothesis.
Answer: The Wobble Hypothesis, proposed by Francis Crick, explains why the genetic code is ambiguous, meaning that a single amino acid can be coded by more than one codon. According to this theory, the first two nucleotide bases of a codon form strong pairs with the anticodon, but the third base pair is less strict or "wobbles." This allows a single transfer RNA (tRNA) molecule to recognize multiple codons that code for the same amino acid, especially if they differ only in their third base. This flexibility makes protein synthesis more efficient.
In simple words: The Wobble Hypothesis says that the third base in a DNA codon doesn't always have to perfectly match the RNA anticodon. This small flexibility lets one type of RNA read several different codons that all code for the same amino acid.

🎯 Exam Tip: The core of the Wobble Hypothesis is the flexible pairing at the third codon position, which explains the degeneracy (redundancy) of the genetic code and allows fewer tRNAs to recognize all codons.

Question 2. Describe the structural changes in chromosomal mutation.
Answer:
Chromosomal mutation or Chromosomal aberration or Numerical changes in chromosomes:
Any change in the arrangement of genes, or the insertion or deletion of a gene within a chromosome, is known as a Chromosomal Mutation. These changes can significantly impact an organism's traits. They are generally categorized into two main types:
1. Change in the number of chromosomes:
This refers to variations in the total count of chromosomes in a cell. This can involve either entire sets of chromosomes (euploidy) or individual chromosomes (aneuploidy).
(1) Euploidy or Polyploidy: This is a type of chromosomal change where an organism has one or more complete extra sets of chromosomes. For example, a triploid has three sets, and a tetraploid has four. Colchicine, derived from the autumn crocus, can induce polyploidy by disrupting spindle fiber formation during cell division, preventing chromosomes from separating and leading to a doubling of chromosome numbers.
(a) Autopolyploidy: In this type, the additional sets of chromosomes come from the same parent species or are identical to the existing sets.
(b) Allopolyploidy: This involves more than two haploid sets of chromosomes that come from different species. For instance, Raphnobrassica (2n = 36), created by Russian scientist G.D. Karpechenko (1927) by crossing radish and cabbage, is an example. Triticale, a cross between wheat and rye, is another well-known man-made cereal that exhibits allopolyploidy.
(2) Aneuploidy: This is the addition or loss of one or more individual chromosomes from the normal diploid set of an organism. It's often caused by non-disjunction, where chromosomes fail to separate correctly during meiosis. This leads to an imbalance in the number of specific chromosomes.
(a) Hypoploidy: This involves the loss of one or more chromosomes from the diploid genome. Losing one chromosome (2n - 1) is called monosomy, while losing a pair of homologous chromosomes (2n - 2) is termed nullisomy.
(b) Hyperploidy: This is the addition of one or more chromosomes. Having one extra chromosome (2n + 1) is called trisomy (e.g., Down's syndrome, which is 21st trisomy or Mongolism). Having two extra chromosomes (2n + 2) is called tetrasomy.
2. Change in the structure of chromosomes:
These changes involve alterations in the arrangement or number of genes or gene locations on a chromosome, without necessarily changing the total chromosome number. They are broadly classified into four types:
(a) Deletion: This is the simplest type of chromosomal aberration, involving the loss of a segment from a chromosome. A terminal deletion occurs when a segment is lost from either end of the chromosome. An intercalary or interstitial deletion involves the loss of a segment from the middle of the chromosome, followed by the rejoining of the remaining terminal segments.
(b) Translocation: This involves the exchange of segments between two non-homologous chromosomes. This exchange can be unilateral (from one chromosome to another) or bilateral (between two chromosomes). Sometimes, a change in gene expression can occur due to a new position on the chromosome, known as a position effect.
(c) Inversion: In this structural change, the number of genes on a chromosome stays the same, but their sequence is reversed due to a 180° rotation of a chromosomal segment. Even though the gene content remains unchanged, the altered sequence can lead to changes in phenotypic characters (observable traits).
(d) Duplication: This occurs when some genes or chromosomal segments are present more than once in a chromosome. This means a segment of a chromosome is repeated, leading to an extra copy of certain genes.
In simple words: Chromosomal mutations are changes in how genes are arranged or the number of chromosomes. This can mean having too many or too few chromosomes, or pieces of chromosomes being lost, added, or moved around.

🎯 Exam Tip: For a detailed answer on chromosomal mutations, categorize changes into numerical and structural types, and then explain each subtype (euploidy, aneuploidy, deletion, translocation, inversion, duplication) with a clear definition.

Question 3. Describe the Human Genome Project.
Answer:
Human Genome Project:
• The Human Genome Project (HGP) was a massive international research effort with the primary goal of mapping and sequencing all 3 billion nucleotide bases that make up the human genome, and identifying all the genes within it. This project greatly advanced our understanding of human biology.
• The project was overseen by an international body, the Human Genome Organization (HUGO), and was jointly initiated in 1988 by the US Department of Energy (DOE) and the National Institute of Health (NIH), officially starting in 1990.
• Over 250 laboratories across 8 countries participated, with key leadership from James D. Watson and Francis Collins. It is often called the "Mega Project" due to its scale and ambition.
The technique used in the Human Genome Project:
There were two main approaches for analyzing the genome:
• Expressed sequence tags (ESTs): This involved identifying all the genes that are expressed as RNA.
• Sequence annotation: This approach focused on sequencing the entire genome (both coding and non-coding regions) and then assigning functions to different regions. This was the primary methodology used.
The second methodology used in the HGP involved the following steps:
• Isolation and Fragmentation: The whole DNA from a cell was extracted and randomly broken into smaller fragments.
• Vector Insertion: These fragments were inserted into specialized vectors, such as Bacterial Artificial Chromosomes (BACs) and Yeast Artificial Chromosomes (YACs), which can carry large DNA segments.
• Cloning: The recombinant vectors containing human DNA fragments were then cloned in suitable hosts like bacteria and yeast, creating many copies. PCR (Polymerase Chain Reaction) was also used for amplifying DNA fragments.
• Sequencing: The cloned fragments were sequenced using automated DNA sequencers based on the Di-deoxy Chain Termination method, developed by Frederick Sanger.
• Assembly: The sequenced fragments were then pieced together based on overlapping regions to reconstruct the full chromosomal sequence.
• Mapping: Physical and genetic mapping used sequence recognition sites of restriction endonucleases on microsatellites to help in accurate assembly.
Salient Features of Human Genome:
• The human genome consists of approximately 3.1657 billion nucleotide base pairs.
• Single Nucleotide Polymorphisms (SNPs) are common variations found, which are useful for identifying disease susceptibility and tracking genetic traits.
• About 50% of the genes' functions have been identified so far.
• Less than 2% of the human genome actually codes for proteins.
• Chromosome number 1 has the highest number of genes (2968), while the Y chromosome has the fewest (231).
• Remarkably, 99.9% of the nucleotide bases are identical among all human beings.
• The small 0.1% variation, amounting to about 3.2 million nucleotides, accounts for the genetic differences observed in humans.
• A significant portion of the human genome consists of repeated or repetitive sequences, including about 30,000 minisatellite loci (11-60 bp repeats) and 200,000 microsatellites (10-100 bp repeats). These repetitive sequences do not directly code for proteins but play roles in chromosome structure, dynamics, and evolution.
In simple words: The Human Genome Project was a huge plan to map all the DNA in humans. Scientists found out how many building blocks (nucleotides) our DNA has, identified all the genes, and learned that most of our DNA is the same, but tiny differences make us unique.

🎯 Exam Tip: When describing the HGP, ensure you cover its goals, key agencies involved, the primary techniques used (especially sequence annotation), and at least 3-4 salient features of the human genome discovered.

Question 4. Explain in detail about DNA fingerprinting technique and write about its applications.
Answer:
DNA Fingerprinting:
• DNA fingerprinting is a method that identifies individuals based on their unique DNA profiles. Just as no two individuals (except identical twins) have identical physical characteristics, each person also has a distinctive DNA pattern. This uniqueness is the basis of this powerful technique.
• While visible traits like skin color, hair color, eye color, height, and walking style help differentiate individuals, the most precise identification comes from DNA. Francis Galton developed the idea of using fingerprints for official identification, which is still in use today.
• In 1985, Alec Jeffreys and his team were studying a human blood protein gene fragment (globin) and discovered that it contained sequences of bases repeated multiple times. This led to the development of modern DNA fingerprinting.
Principle:
• DNA contains numerous small nucleotide sequences that are repeated. These Variable Number of Tandem Repeats (VNTRs) are highly variable in length among individuals. These repetitive sequences are like unique genetic barcodes for each person.
• While two individuals might have VNTRs of the same length, their exact sequences will be different. This distinctiveness forms the core principle.
• Critically, every child inherits half of their VNTRs from their mother and the other half from their father, making it useful for paternity testing.
DNA fingerprinting Technique:
• DNA Isolation: DNA is extracted from biological samples such as blood, saliva, semen, hair, or teeth. This is often done using a high-speed refrigerated centrifuge to separate cellular components.
• DNA Amplification: If the initial DNA amount is small, it can be multiplied using Polymerase Chain Reaction (PCR) to get enough material for analysis.
• Restriction Digestion: The DNA is then cut into smaller fragments using specific restriction endonuclease enzymes. These enzymes recognize and cut DNA at particular sites, leading to Restriction Fragment Length Polymorphisms (RFLPs).
• Gel Electrophoresis: The DNA fragments are loaded into wells on an electrophoresis gel. An electric current is passed through the gel, causing the negatively charged DNA fragments to move towards the positive electrode. Smaller fragments move faster and further, separating the DNA pieces by size.
• Southern Blotting: The separated DNA fragments are then transferred from the gel to a nylon or nitrocellulose membrane. This process is called Southern blotting.
• Hybridization: The membrane is then incubated with a radioactive or fluorescently labeled DNA probe. This probe is designed to bind to specific VNTR sequences.
• Autoradiography: After hybridization, the membrane is exposed to X-ray film. The labeled probes reveal a unique band pattern, creating the "DNA fingerprint."
Application of DNA Fingerprinting:
• Forensic Cases: DNA fingerprinting is a crucial tool in forensics to identify suspects or victims at crime scenes. Samples of bodily fluids (blood, semen), hair, or bone collected from the crime site can be analyzed and compared to suspects' DNA. It helps link suspects to crimes or exonerate innocent individuals.
• Disputed Parentage: This technique is invaluable for resolving paternity and maternity disputes. By comparing the child's DNA with that of the alleged parents, genetic relationships can be confirmed or denied.
• Criminal Investigations: Beyond identification, it aids in various criminal cases like murder, rape, and property disputes, especially when identifying individuals involved is critical.
• Medical Field: DNA fingerprinting can detect genetic markers for several hereditary diseases early in pregnancy. This allows for potential management or intervention strategies.
• Population Studies: It is also used in anthropological studies to trace migration patterns of ancient populations and to analyze genetic variations among different strains of agricultural crops and animals.
In simple words: DNA fingerprinting uses the fact that everyone's DNA pattern is unique to identify people. It involves taking DNA, cutting it into pieces, sorting them by size, and then finding specific repeating parts to create a unique "fingerprint." It helps solve crimes, prove who a child's parents are, and even detect diseases early.

🎯 Exam Tip: When explaining DNA fingerprinting, describe each step of the technique (isolation, amplification, digestion, electrophoresis, blotting, hybridization, autoradiography) and then list its key applications in both forensic and medical fields.

What do you mean by cloning? Explain how first animal clone was produced?
Answer: Cloning is the process of creating a group of cells or organisms that are exact copies, both physically and genetically, of a single parent. The word "Klon" comes from Greek, meaning "cutting," which describes how new organisms can be made from a part of an existing one. Simple organisms can clone themselves naturally, but this does not happen naturally in more complex animals. Identical twins are a natural form of cloning, as they develop when a single fertilized egg divides into two separate embryos. For plants, tissue culture is a method of cloning where a single cell from a plant is grown in a special medium to produce a new plant. This technique is important for propagating desirable plant traits.
Process of Cloning of Dolly:
In 1995, scientists Ian Wilmut and his team worked on cloning sheep, creating the Magon and Morgan clones through nuclear transplantation at the Roslin Institute in Scotland. They achieved a major breakthrough in February 1997 by successfully producing "Dolly," the first clone of an adult lamb. Later, in July 1997, Wilmut's team also cloned sheep named Polly and Molly. These clones were made using a single cell taken from the udder of an adult sheep, proving that adult cells could be reprogrammed to create a new organism. The success with Dolly greatly advanced the understanding of cell differentiation and cloning capabilities.
In simple words: Cloning is making an exact copy of a living thing from one parent. Simple creatures clone naturally, but complex animals usually do not. Identical twins are natural clones from one egg. For plants, we can grow new plants from a single cell. Dolly the sheep was the first animal cloned from an adult cell in 1997 by Ian Wilmut. This showed that cells from an adult body could be used to make a whole new animal, which was a huge discovery.

🎯 Exam Tip: When defining cloning, remember to mention both the genetic similarity and the origin from a single parent. For Dolly, highlight the key scientists, date, and the significance of using an adult cell rather than an embryonic one.

Question 6. Explain in detail changes in chromosomal numbers.
Answer: Changes in the number of chromosomes can happen in two main ways: Euploidy (also known as Polyploidy) and Aneuploidy.
(1) Euploidy or Polyploidy: This is a type of change where an organism gains one or more complete sets of chromosomes, which are usually derived from the same parent species. For example, plants can become triploid (having three sets), tetraploid (four sets), or pentaploid (five sets) of chromosomes. The chemical colchicine, extracted from the autumn crocus plant, can prevent spindle fibers from forming during cell division, causing chromosomes to not separate properly. This leads to the doubling of the chromosome number, often resulting in larger, more vigorous plants.
(b) Allopolyploidy: In this type, an organism gains more than two haploid sets of chromosomes that are different and come from different species. For instance, Raphnobraccia (2n = 36) was created by Russian scientist G. D. Carpichako in 1927 by crossing a radish (Raphanus sativus) and a cauliflower (Brassica oleracea); however, the resulting hybrid was sterile. Triticale, a human-made cereal grain from crossing wheat (Triticum) and rye (Secale), is another example, now widely grown commercially. This demonstrates how combining genetic material from different species can create new forms.
(2) Aneuploidy: Aneuploidy refers to the addition or loss of one or more individual chromosomes to a cell's complete diploid set. This condition is caused by non-disjunction, meaning chromosomes fail to separate properly during cell division, leading to an incorrect number of chromosomes. Aneuploidy is categorized into two main types:
(a) Hypoploidy: This involves the loss of one or more chromosomes from the normal diploid genome. If one chromosome is missing (2n - 1), the condition is called monosomy. If a whole pair of chromosomes is lost (2n - 2), it is called nullisomy.
(b) Hyperploidy: This involves the addition of one or more extra chromosomes. Having one extra chromosome is called trisomy. A well-known example is Down's syndrome, also known as 21st trisomy, where there is an extra copy of chromosome 21. If two extra chromosomes are present, it is called tetrasomy (2n + 2). Understanding these chromosomal changes helps explain various genetic disorders and traits.
In simple words: Changes in the number of chromosomes happen in two main ways. Euploidy is when a cell gets whole extra sets of chromosomes, like having three or four full copies instead of two. This often makes plants bigger and stronger. Aneuploidy is when a cell has one extra chromosome or is missing one, not a whole set. This can lead to genetic conditions like Down's syndrome. Both changes happen because chromosomes do not separate correctly when cells divide.

🎯 Exam Tip: Clearly differentiate between euploidy (changes in whole sets of chromosomes) and aneuploidy (changes in individual chromosomes). Provide examples for each, such as triploidy or tetraploidy for euploidy, and trisomy (like Down's syndrome) for aneuploidy, to illustrate your explanation.