Mutation Questions in English

(D) Mutations are permanent alterations in the $DNA$ sequence of an organism.
All living organisms,including $Bacteria$,$Viruses$ (which contain genetic material),and $Fungi$,are capable of undergoing mutations.
These mutations can occur spontaneously due to errors during $DNA$ replication or be induced by mutagenic agents such as radiation or chemicals.
Therefore,all the listed organisms can produce mutants.

(A) $Mutator$ $gene$ is a type of gene that increases the spontaneous mutation rate of other genes in an organism.
These genes often encode proteins involved in $DNA$ replication or repair mechanisms.
When these genes are mutated,the fidelity of $DNA$ replication decreases,leading to a higher frequency of mutations in the genome.

(B) Harmful mutations that are recessive are not eliminated from the gene pool because they are masked by the dominant allele in heterozygous individuals. Since the phenotype is not expressed in the heterozygote,natural selection cannot act upon it to remove it from the population. These alleles remain hidden in the gene pool and can be passed on to future generations.

(C) Mutation refers to sudden,stable,and heritable (transmissible) discontinuous variations that appear in an organism due to a permanent change in its genotype. Therefore,it is defined as a change in heritable characters.

(C) Gene mutations are sudden,stable changes in the structure of a gene or cistron.
These mutations occur due to alterations in the type or sequence of nucleotides within the $DNA$ molecule.
Since nitrogenous bases are the primary components of nucleotides,any change in their sequence directly alters the genetic code,leading to a gene mutation.

(D) mutation is defined as a sudden,heritable change in the $DNA$ sequence of an organism.
These changes are stable and are passed on to the next generation,meaning they 'breed true'.
Therefore,the concept of sudden genetic change that is inherited is known as the principle of mutations.

(D) Mutations are sudden,heritable changes in the $DNA$ sequence of an organism. They can occur in any cell of the body,whether somatic or germinal,when exposed to mutagenic agents such as radiation (e.g.,$X$-rays,$UV$ rays). Therefore,any cell of the body exposed to radiation has the potential to undergo a mutation.

(D) Hugo de Vries proposed the "Mutation Theory" of evolution.
He conducted his experiments on the evening primrose, $Oenothera \, lamarckiana$.
He observed sudden, heritable changes in the phenotype of this plant, which he termed as mutations.

(D) Sickle-cell anaemia is a classic example of a point mutation. It is an autosomal recessive genetic disorder caused by a single nucleotide substitution ($GAG$ to $GUG$) in the $\beta$-globin gene of haemoglobin. This mutation results in the replacement of glutamic acid with valine at the sixth position of the $\beta$-globin chain,leading to the formation of abnormal haemoglobin $(HbS)$.

(D) point mutation is a type of mutation that causes a single nucleotide base substitution,insertion,or deletion of the genetic material,$DNA$ or $RNA$.
Specifically,it involves a change in a single base pair of a gene.
An example of a point mutation is the substitution of a single base in the gene for beta-globin,which causes sickle cell anemia.

(B) $Mutation$ is defined as a sudden heritable change in the $DNA$ sequence of an organism.
These changes introduce new alleles into the gene pool,which leads to genetic diversity.
Therefore,$Mutation$ is a primary source of variations in organisms,which provides the raw material for evolution and natural selection.

(B) mutagen is a physical or chemical agent that increases the frequency of mutations in an organism.
$Ethyl$ $methane$ $sulphonate$ $(EMS)$,$Nitrous$ $acid$,and $Ethylene$ $oxide$ are well-known chemical mutagens that can alter $DNA$ structure.
$Acetic$ $acid$ is a weak organic acid commonly found in vinegar and does not possess mutagenic properties under normal biological conditions.
Therefore,$Acetic$ $acid$ is not a mutagen.

(D) Mutation rates are influenced by various mutagenic factors.
$1$. Physical mutagens such as $X$-rays,gamma rays,and beta radiation can cause structural changes in $DNA$,thereby increasing the mutation rate.
$2$. Environmental factors like temperature can also affect the stability of $DNA$ and the activity of enzymes involved in $DNA$ replication and repair,which in turn influences the rate of mutation.
Since all the given options are known to affect mutation rates,the correct answer is $D$.

(D) Mutation is a sudden heritable change in the gene structure of an organism. The term $Genetic$ $mutation$ is the broad category that encompasses both $Somatic$ $mutation$ (occurring in body cells) and $Germinal$ (or $Zygotic$) $mutation$ (occurring in reproductive cells). Therefore,$Genetic$ $mutation$ is the primary classification.

(C) Gene duplication is a type of chromosomal mutation. It occurs when an extra copy of a gene is generated,often due to unequal crossing over during meiosis. This phenomenon has been observed in the giant polytene chromosomes of the salivary glands of $Drosophila$.

(D) The nitrogenous bases in $DNA$ $(A, T, G, C)$ can exist in rare alternative structural forms known as tautomers.
These tautomeric shifts involve the migration of a hydrogen atom (proton) and a shift in a double bond within the molecule.
This phenomenon is known as tautomerization.
When these bases exist in their rare tautomeric forms,they can form incorrect base pairs (e.g.,$A$ pairing with $C$ instead of $T$),which can lead to mutations during $DNA$ replication.
Therefore,the correct term for these rearrangements is tautomerisational mutation.

(D) The correct answer is $D$.
$1)$ Induced mutations are alterations in the gene after it has come in contact with mutagens or environmental factors. Mutagens can be chemical (e.g.,nitrous acid) or physical (e.g.,$X$-rays).
$2)$ $A$ mutation that occurs by itself without being affected by an external mutagen is called a spontaneous mutation (e.g.,errors during $DNA$ replication).
$3)$ Since the question specifies that the mutation is caused by a mutagen,it is classified as an induced mutation.
$4)$ Natural or spontaneous mutations are those that occur due to internal factors,whereas mutations caused by external agents are termed induced mutations.

(A) Discontinuous variations are those that appear suddenly in a population and are not connected by intermediate forms.
These variations are primarily caused by $Mutations$,which are sudden,heritable changes in the $DNA$ sequence.
Unlike continuous variations (which show a range of phenotypes),discontinuous variations result in distinct,clear-cut categories.
Therefore,the correct option is $A$.

(D) The correct answer is $D$. $A$ suppressor mutation is a secondary mutation that alleviates or reverts the phenotypic effects of an already existing mutation. It restores the function lost by the primary mutation and is located at a genetic site different from the original mutation site.

(C) The original chromosome segment order is $A-B-C-D-E$.
In the mutated chromosome,the segment $B-C-D$ has been reversed to $D-C-B$.
This type of chromosomal mutation,where a segment of a chromosome breaks off and is reinserted in the reverse orientation,is known as Inversion.
Therefore,the correct option is $C$.

(B) Mutation is defined as a sudden,heritable change in the genetic material ($DNA$ sequence) of an organism.
Since mutations occur in the $DNA$,they are passed on from one generation to the next,provided they occur in the germline cells.
Therefore,mutations are changes that are inherited.

(A) Aniridia is a rare genetic disorder characterized by the complete or partial absence of the iris in the eye.
It is primarily caused by a mutation in the $PAX6$ gene.
This condition follows an autosomal dominant pattern of inheritance,meaning that a single copy of the mutated gene is sufficient to cause the disorder.
Therefore,it is classified as a dominant mutation.

(D) In transition mutation,a nitrogenous base is replaced by another base of the same chemical category.
This means a purine is replaced by another purine $(A \rightleftharpoons G)$ or a pyrimidine is replaced by another pyrimidine $(C \rightleftharpoons T)$.
In option $(d)$,$AT$ ($A$ is a purine,$T$ is a pyrimidine) is replaced by $GC$ ($G$ is a purine,$C$ is a pyrimidine).
Specifically,$A$ is replaced by $G$ (purine to purine) and $T$ is replaced by $C$ (pyrimidine to pyrimidine),which fits the definition of a transition.

(B) The correct answer is $B$.
Genetic mutation involves a permanent alteration in the $DNA$ sequence,such as a change in the configuration or position of nucleotides.
Once a mutation occurs,the original genetic sequence is lost,making the process irreversible under normal biological conditions.
While a 'reverse mutation' or 'back mutation' can occur to restore the original phenotype,the original mutation event itself remains an irreversible change to the genome.

(C) The primary source of all genetic variation is $Mutation$.
$Mutation$ refers to a sudden, heritable change in the $DNA$ sequence of an organism.
While $Independent \text{ } assortment$ and $Recombination$ (during meiosis) shuffle existing alleles to create new combinations, they do not create new alleles.
$Mutation$ is the ultimate process that introduces entirely new alleles into a population's gene pool, thereby serving as the fundamental source of genetic diversity.

(D) In the first mutation: $UAU\ ACC\ UAU$ changes to $UAU\ AAC\ CUA$. Here,the deletion of the first '$C$' in '$ACC$' causes a shift in the reading frame,resulting in a frame shift mutation.
In the second mutation: $UUG\ CUA\ AUA$ changes to $UUG\ CUG\ AUA$. Here,the '$A$' in '$CUA$' is replaced by '$G$',changing the codon to '$CUG$'. Since a purine is replaced by another purine (or pyrimidine by pyrimidine),this is a transition mutation.
Therefore,the mutations are frame shift and transition respectively. The correct option is $D$.

(C) Translocation is a type of chromosomal rearrangement in which a segment of a chromosome breaks off and attaches to another chromosome (either homologous or non-homologous). This process results in the transfer of a block of genes from one linkage group to another,leading to structural changes in the genome.

(C) $5$-bromouracil ($5$-$BU$) is a base analogue of thymine.
Base analogues are chemical compounds that structurally resemble the nitrogenous bases of $DNA$.
Because of their structural similarity,they can be incorporated into the $DNA$ molecule during replication in place of normal bases,leading to mutations such as transitions.

(C) The original $DNA$ sequence is $ATG\ ATG\ ATG$.
When a cytosine $(C)$ base is inserted at the beginning,the sequence becomes $C\ ATG\ ATG\ ATG$.
This is an example of an insertion mutation.
Since the reading frame is shifted by one base,the new codons formed are $CAT$,$GAT$,$GAT$,and the remaining $G$ base.
Therefore,the resulting sequence is $CAT\ GAT\ GAT\ G$.

(A) In a transition mutation,a purine ($A$ or $G$) is replaced by another purine,or a pyrimidine ($C, T$ or $U$) is replaced by another pyrimidine.
Since adenine $(A)$ and guanine $(G)$ are both purines,the replacement of adenine by guanine is classified as a transition mutation.

(D) Starfish typically exhibit pentamerous (five-armed) radial symmetry. The presence of six arms in a starfish is a deviation from the normal body plan. This change in the genetic makeup or the expression of genes during development that results in an abnormal number of appendages is classified as a mutation. While variation refers to differences between individuals,a specific structural anomaly like an extra arm is best described as a mutation.

(D) Mutations are sudden,heritable changes in the $DNA$ sequence. In nature,most mutations are either neutral (having no effect on fitness) or harmful (deleterious) to the organism. Beneficial mutations are extremely rare. Therefore,the occurrence of mutations is mostly neutral or harmful.

(D) mutation that changes the wild-type allele to a mutant allele is known as a forward mutation.
Conversely,a mutation that changes a mutant allele back to the wild-type allele is called a reverse mutation or back mutation.
Therefore,the correct option is $D$.

(A) $H.J. Muller$ was awarded the Nobel Prize in Physiology or Medicine in $1946$ for his discovery that mutations can be induced by $X$-rays. This groundbreaking work demonstrated that ionising radiation acts as a mutagen,significantly advancing our understanding of genetics and the mechanisms of evolution.

(D) mutation is defined as a sudden,heritable change in the genetic material $(DNA)$ of an organism.
These changes are stable and are passed on to the next generation,meaning they 'breed true'.
According to Hugo de Vries,mutations are the raw material for evolution and are responsible for the sudden appearance of new variations in a species.

(C) Mutations are sudden,heritable changes in the $DNA$ sequence of an organism.
They introduce new alleles into a population,which leads to genetic variation.
Genetic variation is the raw material for evolution,as it provides the diversity upon which natural selection acts.
Therefore,mutations are primarily responsible for creating variation in organisms.

(A) change in the chromosome number is referred to as chromosomal mutation or chromosomal aberration.
Chromosomal mutation involves changes in the structure or the number of chromosomes.
When the number of chromosomes changes,it can be due to aneuploidy (gain or loss of one or more chromosomes) or polyploidy (increase in the number of complete sets of chromosomes).
Therefore,the most appropriate general term among the given options is chromosomal mutation.

(A) Hereditary variations (mutations) in plants are induced by exposing them to mutagenic agents. $X$-rays are high-energy ionizing radiations that cause changes in the $DNA$ sequence of the plant genome. This technique is widely used in mutation breeding to create genetic variability,which can then be selected for desirable traits. Gibberellic acid and Auxins are plant growth regulators,and $D.D.T.$ is an insecticide,none of which are primarily used to induce hereditary mutations.

(A) Hermann $J$. Muller was the scientist who first demonstrated that $X$-rays could induce mutations in organisms. In $1927$, he conducted experiments on the fruit fly, $(Drosophila \text{ } melanogaster)$, and showed that exposure to $X$-rays significantly increases the rate of mutations. This discovery was a landmark in the field of genetics and earned him the Nobel Prize in Physiology or Medicine in $1946$.

(C) Gene mutation,also known as point mutation,refers to a permanent alteration in the $DNA$ sequence that makes up a gene.
This change occurs at the molecular level due to a change in the sequence of nitrogenous bases (e.g.,substitution,insertion,or deletion).
Such mutations can lead to variations in the phenotype of an organism and have been historically utilized in plant breeding for crop improvement.

(C) Mutations are changes in the genetic material of an organism.
They can be induced artificially using physical or chemical mutagens.
Among the options provided,$Gamma$ rays are high-energy ionizing radiations commonly used in plant breeding to induce mutations.
$Alpha$ and $Beta$ rays have lower penetrating power compared to $Gamma$ rays,and white light does not possess sufficient energy to induce mutations effectively.

(C) Micro-mutations are small,subtle changes that occur in the genetic material $(DNA)$ of an organism.
These mutations involve changes in individual genes,often referred to as point mutations or gene mutations.
Unlike macro-mutations,which involve large-scale chromosomal changes or polyploidy,micro-mutations result in minor phenotypic variations.
Therefore,micro-mutations are defined as changes in genes.

(D) Chemical mutagens are substances that increase the rate of mutation.
Among the given options, $Caffeine$ is a well-known chemical mutagen that can induce mutations in $DNA$.
$Methane$ is a simple hydrocarbon, $Guanine$ is a nitrogenous base found in $DNA$, and $Carbon \text{ } tetrasulphide$ is not typically classified as a potent mutagen in biological contexts.
Therefore, $Caffeine$ is the correct answer.

(C) Mutations are sudden heritable changes in the $DNA$ sequence.
When mutations occur naturally without any external influence, they are called $Spontaneous \text{ mutations}$.
When mutations are artificially caused by external physical or chemical agents known as $mutagens$ (e.g., $X-rays$, $UV \text{ rays}$, $EMS$), they are referred to as $Induced \text{ mutations}$.
Therefore, mutations caused by mutagenic agents are termed as $Induced \text{ mutations}$.

(D) mutation is defined as a sudden,heritable change in the genetic material of an organism. At the molecular level,a mutation is caused by a change in the base sequence of $DNA$. While radioactive substances,chemicals,and radiations act as 'mutagens' (agents that induce mutations),the fundamental biological event that constitutes a mutation is the alteration of the nucleotide base sequence.

(B) $H.J. Muller$ $(USA)$ was awarded the Nobel Prize in $1946$ for his discovery that $X-$rays induce mutations. This work established the field of radiation genetics and demonstrated that high-energy radiation can cause genetic damage,specifically sex-linked recessive lethal mutations in $Drosophila$.

(A) $Phenocopy$ is an individual whose phenotype (observable characteristics) has been modified by environmental conditions to resemble the phenotype of a different genotype. Even though the genetic makeup $(genotype)$ remains different,the environmental influence causes the organism to express a trait that is typically associated with a different set of genes. Therefore,when different genotypes exhibit the same phenotype due to environmental factors,it is called a $Phenocopy$.

(B) An $Auxotroph$ is a mutant microorganism that has lost the ability to synthesize a specific nutrient (such as an amino acid or vitamin) required for its growth due to a mutation in the gene responsible for that pathway.
However,it can grow if the specific nutrient is supplied in the growth medium.
In contrast,a $Prototroph$ is a wild-type strain that can synthesize all its required nutrients from simple inorganic sources.

(C) Hugo de Vries, a Dutch botanist, proposed the Mutation Theory of evolution based on his experimental work on the evening primrose, $Oenothera \text{ } lamarckiana$.
He observed sudden, heritable changes in the population of this plant, which he termed as 'mutations'.
These mutations are the raw material for evolution, according to his theory.

(C) Sickle cell anemia is an autosomal recessive genetic disorder. It is caused by a single base pair substitution in the $\beta$-globin gene of hemoglobin. Specifically,the codon $GAG$ is replaced by $GUG$ at the sixth position of the $\beta$-globin chain. This results in the substitution of glutamic acid with valine. Since this mutation involves a change in a single nucleotide base pair,it is classified as a point mutation.