Mutation Questions in English

(D) Mutagens are physical or chemical agents that increase the rate of mutation.
$UV$ rays are physical mutagens that cause thymine dimers in $DNA$.
Mustard gas is a well-known chemical mutagen.
Nicotine is a stimulant found in tobacco,but it is not classified as a mutagen.
Therefore,nicotine cannot be considered a mutagen.

(B) Sickle cell anemia is an autosomal recessive genetic disorder 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 change results in the substitution of glutamic acid with valine at the sixth position of the protein.
Since this mutation involves a change in a single nucleotide base pair,it is classified as a point mutation.

(A) Genetic material $(DNA)$ is generally stable and remains constant throughout the life of an organism. Changes in genetic material occur due to mutations,which can be caused by physical or chemical agents $(mutagens)$. Options $A$,$B$,$C$,and $D$ describe conditions or processes that do not inherently alter the sequence or structure of the $DNA$ molecule in a way that constitutes a permanent genetic change. However,if the question implies what causes a change,and given the provided options,it is important to note that none of the options $B, C,$ or $D$ cause mutations. Option $A$ is a statement of fact regarding stability. In the context of standard biology,genetic material changes only through mutations or recombination events.

(D) $DNA$ replication is a highly accurate process,but errors can occur during the copying of the genetic code.
When an incorrect nucleotide is incorporated into the new $DNA$ strand and remains uncorrected by $DNA$ polymerase proofreading mechanisms,it results in a permanent change in the $DNA$ sequence.
This permanent change in the genetic material is known as a mutation.
Therefore,errors in replication are a primary source of mutations.

(C) Deletion or rearrangement in a segment of $DNA$ results in a mutation.
Such mutations can alter the reading frame of the genetic code (frameshift mutation) or change the sequence of amino acids in the resulting protein.
This alteration often leads to the loss of function of the gene product or,in some cases,a gain of function,which significantly impacts the phenotype of the organism.

(A) point mutation is a genetic mutation where a single nucleotide base is changed,inserted,or deleted from a $DNA$ or $RNA$ sequence of an organism's genome.
Specifically,it involves the substitution,addition,or deletion of a single base pair in a gene.
This can lead to changes in the amino acid sequence of the protein being synthesized,potentially affecting its function.
Therefore,the correct option is $A$.

(B) The rate of appearance of new forms (variations) in a population is primarily driven by $Mutation$.
$Mutation$ is a sudden,heritable change in the genetic material $(DNA)$ of an organism.
These changes introduce new alleles into the gene pool,which serve as the raw material for evolution.
While $Natural$ $selection$ acts upon these variations to determine which are advantageous,the actual generation of new genetic forms is fundamentally linked to the process of $Mutation$.

(B) Hugo de Vries, a Dutch botanist, proposed the mutation theory of evolution. He conducted his experiments on the plant $Oenothera \text{ lamarckiana}$, which is commonly known as the Evening Primrose. He observed sudden, heritable changes in the population of this plant, which he termed as mutations.

(D) According to the modern synthetic theory of evolution,mutations are the raw material for evolution. Mutations are defined as sudden,heritable changes in the genetic material of an organism. These changes occur randomly and are directionless,meaning they do not occur to fulfill a specific need of the organism. Therefore,the correct description for mutation is that it is directionless and random.

(C) Transposons are known as jumping elements that have the ability to move within the genome.
When these transposable elements get inserted into or near genes,they can disrupt the gene sequence or alter gene expression.
This insertion results in a change in the allele,which is a primary cause of genetic variation and mutation.

(B) mutation is defined as a sudden,heritable change in the $DNA$ sequence of an organism.
Mutations can lead to the development of new varieties,the creation of disease-resistant plants,and can influence recombination processes.
However,regeneration is a physiological process involving the regrowth of lost body parts or tissues,which is controlled by developmental and cellular signaling pathways,not by mutation.
Therefore,mutation is not able to cause regeneration.

(B) Mutation is a phenomenon by which genetic variation is achieved through changes in the base sequences within genes,which creates a new character or trait absent in the parental generation.
Mutations that occur naturally are called spontaneous mutations,and those that are induced artificially are called induced mutations.
The application of induced mutation for crop improvement is called mutation breeding.

(B) When a mutation is confined to only one base pair substitution,deletion,or insertion,it is called a point mutation.
Sickle-cell anaemia is a classic example of a point mutation,in which the amino acid Glutamic acid $(Glu)$ is replaced by Valine $(Val)$ at the sixth position of the $\beta$-globin chain of the haemoglobin molecule.

(D) Sickle-cell anaemia is a classic example of a point mutation.
It is caused by a single base pair substitution in the gene coding for the $\beta$-globin chain 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 the amino acid glutamic acid with valine,which leads to the formation of abnormal hemoglobin $(HbS)$ and causes the red blood cells to become sickle-shaped under low oxygen tension.

(A) $H.J. Muller$ provided the first definite experimental proof that $X$-rays can induce mutations in organisms. He demonstrated this using the fruit fly, $Drosophila \text{ } melanogaster$, in $1927$, for which he was later awarded the Nobel Prize.

(D) Mutagens are agents that induce mutations by causing changes in the $DNA$ sequence.
They can be classified into two main categories:
$1$. Physical agents: Such as $UV$-radiation,$X$-rays,and gamma rays.
$2$. Chemical agents: Such as acridine dyes,base analogs,and alkylating agents.
Therefore,since both physical and chemical agents can cause mutations,the correct answer is $(D)$.

(A) Mutation is the ultimate source of variation in $DNA$,as proposed by Hugo de Vries.
Linkage refers to the physical association of genes on the same chromosome,which tends to keep parental combinations together rather than creating new variations.
Mitosis is a process of equational division that produces genetically identical daughter cells,thus it does not contribute to genetic variation.
Therefore,mutation is the primary phenomenon responsible for variation.

(C) Inversion is a type of chromosomal mutation where a segment of a chromosome breaks off, rotates $180^{\circ}$, and reattaches to the same chromosome. This results in the reverse order of genes within that specific segment of the chromosome.

(B) By comparing the original $DNA$ sequence $(A-A-C-T-G-A-T-C-C-A)$ with the mutated sequence $(A-A-C-T-G-T-A-T-C-C-A)$,we can observe that an extra nucleotide base '$T$' has been added into the sequence.
This addition of a nucleotide base into the $DNA$ sequence is known as an insertion mutation.

(A) change in a single base pair of $DNA$ is known as a point mutation. Due to the degenerate nature of the genetic code,where multiple codons can code for the same amino acid,a single base substitution may result in a synonymous mutation (silent mutation). In such cases,the amino acid sequence remains unchanged,and consequently,the phenotype may not change.

(B) point mutation is a type of mutation that causes a single nucleotide base change,insertion,or deletion of the genetic material,$DNA$ or $RNA$.
Specifically,a mutation that occurs due to a change in a single base pair of $DNA$ is known as a point mutation.
$A$ classic example of this is Sickle-cell anaemia,where a single base pair substitution ($GAG$ to $GTG$) in the gene for $\beta$-globin results in the replacement of glutamic acid with valine in the haemoglobin protein.

(C) Inversions occur when there are two breaks in a chromosome and the intercalary segment reunites in a reverse order by rotating at $180^{\circ}$.

(B) Translocation is a type of chromosomal mutation where a segment of one chromosome breaks off and attaches to a non-homologous chromosome.
$1$. Option $A$ shows an inversion,where a segment of the chromosome is reversed.
$2$. Option $B$ shows a translocation,where a segment $(T, U, V, W)$ from chromosome $1$ has been transferred to chromosome $2$.
$3$. Option $C$ shows a deletion,where a gene $(G)$ is missing.
$4$. Option $D$ shows a duplication,where a segment $(G, H)$ is repeated.
Therefore,the correct result of a translocation is represented by option $B$.

(D) dominant lethal gene is a mutation that results in the death of an organism that carries the allele,even if only one copy is present (heterozygous state). Therefore,it kills the organism.

(A) The original gene sequence is $P-Q-R-S-T-U-V-W$.
According to the diagram,the chromosome breaks between $Q$ and $R$,and between $U$ and $V$.
The segment between these break points is $R-S-T-U$.
In an inversion mutation,this segment is rotated by $180^{\circ}$,reversing its order to $U-T-S-R$.
Therefore,the new gene sequence becomes $P-Q-U-T-S-R-V-W$.

(D) Mutation is defined as a sudden change in the $DNA$ sequence.
$1$. $A$ change in the $DNA$ sequence directly alters the genotype of an organism.
$2$. Since the genotype determines the protein synthesis and cellular functions,a change in genotype often leads to a change in the phenotype (observable characteristics).
$3$. Metabolic processes are controlled by enzymes,which are proteins encoded by genes. Therefore,a mutation can also alter metabolic pathways.
$4$. Thus,mutation can result in changes in genotype,phenotype,and metabolism.

(C) frameshift mutation is a genetic mutation caused by the insertion or deletion of a number of nucleotides in a $DNA$ sequence that is not divisible by three.
Because the genetic code is read in triplets (codons),the insertion or deletion of one or two base pairs shifts the reading frame of the entire sequence downstream from the mutation site.
As shown in the diagram:
Condition $I$: If there is an insertion of one base,the original sequence $ATC-GAT-CTG$ changes to $ATC-GAT-TCT-G...$,altering all subsequent codons.
Condition $II$: If there is a deletion of one base,the original sequence $ATC-GAT-CTG$ changes to $ATC-GTC-TG...$,also altering all subsequent codons.
Therefore,both deletion and insertion of base pairs lead to a frameshift mutation.

(A) chimera is an organism that contains two or more genetically distinct cell populations derived from different zygotes or through somatic mutations.
In the context of developmental biology,chimerism often arises due to somatic mutations occurring during early embryonic development,where a mutation in a single cell line leads to a mosaic or chimeric phenotype in the adult organism.
Therefore,somatic mutations are a primary cause for the formation of chimeric tissues within an individual.

(C) Mutagens are agents that cause mutations. They are classified into physical and chemical mutagens.
$1$. Physical mutagens include radiations such as $UV$-rays,$X$-rays,and gamma rays.
$2$. Chemical mutagens include substances like acridines,$HNO_2$ (nitrous acid),and base analogues.
Therefore,$UV$-rays are physical factors that induce mutation.

(A) Sickle-cell anaemia is a point mutation caused by the substitution of a single nucleotide base in the gene coding for the $\beta$-globin chain of haemoglobin.
Specifically,at the $6^{th}$ position of the $\beta$-globin chain,the codon $GAG$ is replaced by $GUG$.
This results in the substitution of glutamic acid with valine in the protein sequence.
This change is a result of a transversion mutation where the nucleotide $A$ (adenine) is replaced by $T$ (thymine) in the $DNA$ sequence,leading to the change in the mRNA codon from $GAG$ to $GUG$.

(B) mutant offspring is an individual that possesses a genetic trait or genotype not present in the parents,typically resulting from a mutation. In the given options,the cross $tt \times tt$ involves two homozygous recessive parents. Under normal Mendelian inheritance,the offspring should only be $tt$. The appearance of a $Tt$ offspring from $tt \times tt$ parents indicates a mutation occurred in one of the gametes,making this the correct choice.

(A) frame shift mutation occurs when the addition or deletion of one or more nucleotide bases in a $DNA$ sequence causes a shift in the reading frame of the genetic code.
Since the genetic code is read in triplets (codons),changing the number of bases by a value not divisible by $3$ alters the entire sequence of amino acids downstream from the mutation site.

(C) Mutation is defined as a sudden,heritable change in the genetic material of an organism.
Since mutations alter the $DNA$ sequence (genotype),they frequently result in changes to the observable characteristics or traits of the organism (phenotype).
Therefore,mutations bring about changes in both the genotype and the phenotype of an organism.

(B) Hugo de Vries proposed the mutation theory based on his work on the plant $Oenothera \, lamarckiana$, which is commonly known as the Evening primrose.
He observed that new species arise due to sudden, large, and heritable changes in the genetic material, which he termed as mutations.

(C) Sickle cell anaemia is caused by a point mutation in the $\beta$-globin gene of haemoglobin.
In the normal $Hb^A$ gene,the codon is $GAG$,which codes for Glutamic acid.
In the mutant $Hb^S$ gene,a point mutation changes $GAG$ to $GUG$ in the $mRNA$.
This results in the substitution of Valine for Glutamic acid at the sixth position of the $\beta$-globin chain.
Therefore,the Assertion is correct,but the Reason is incorrect because it states the codons in reverse ($GAG$ instead of $GUG$ for $Hb^S$).

(D) Mutation is a phenomenon which results in alteration of $DNA$ sequences and consequently results in changes in the genotype and the phenotype of an organism.
In addition to recombination,mutation is another phenomenon that leads to variation in $DNA$.
Therefore,all the given statements correctly describe the nature and consequences of mutation.

(D) mutation that involves a change in a single base pair of $DNA$ is called a $Point$ mutation.
For example,the classic case of $Sickle-cell$ $anemia$ is caused by a single base pair substitution in the gene for $\beta-globin$ chain,where $GAG$ is replaced by $GUG$.

(C) The deletion or insertion of base pairs of $DNA$ results in a frame-shift mutation.
This occurs because the genetic code is read in triplets (codons).
When one or two base pairs are added or removed,the entire reading frame of the $mRNA$ sequence downstream of the mutation is shifted.
This leads to the translation of a completely different sequence of amino acids,often resulting in a non-functional protein.

(B) Agents that induce mutations are known as $Mutagens$.
$Mutagens$ can be physical (e.g.,$UV$ radiation,$X$-rays) or chemical (e.g.,base analogs,alkylating agents) in nature.
$Carcinogens$ are agents that cause cancer,$Antigens$ are substances that trigger an immune response,and $Allergens$ are substances that cause allergic reactions.

(A) Mutations are sudden changes in the genetic material of an organism.
Physical mutagens are agents that cause mutations,and among the options provided,$UV$ rays (ultraviolet radiation) are the most common physical mutagens that cause damage to $DNA$ by forming pyrimidine dimers.
$Alpha$ and $Beta$ rays are ionizing radiations,but $UV$ rays are more frequently associated with environmental mutagenesis in biological systems.

(C) sudden large change in the genetic makeup of a population is known as $Mutation$.
$Mutation$ is a sudden, heritable change in the $DNA$ sequence of an organism.
According to Hugo de Vries, mutations are the primary cause of evolution, leading to speciation (saltation).
Natural selection acts on these variations, but the sudden appearance of new traits is primarily due to mutations.

(D) In genetics,the unmodified allele that represents the original phenotype is known as the $wild$ type allele.
When a mutation occurs,the modified allele is generally referred to as the $mutant$ allele.
Therefore,the correct sequence is $wild$ and $mutant$.

(A) Mutation is defined as a phenomenon which results in alteration of $\text{DNA}$ sequences and consequently results in changes in the genotype and the phenotype of an organism.
Since mutation directly changes the genetic material $(\text{DNA})$,it leads to variations in the genetic makeup (genotype) and the observable traits (phenotype) of the organism.
Therefore,both the Assertion $(A)$ and the Reason $(R)$ are correct,and $(R)$ is the correct explanation of $(A)$.

(D) Hugo de Vries, a Dutch botanist, proposed the Mutation theory of evolution.
He conducted his experiments on the evening primrose plant, scientifically known as $Oenothera \, lamarkiana$.
According to this theory, evolution is a discontinuous process that occurs due to large, sudden, and heritable changes in the genetic material, which he termed as mutations.

(D) Hugo de Vries, a Dutch botanist, proposed the 'Mutation Theory' of evolution.
He conducted his experiments on the evening primrose plant, scientifically known as $Oenothera$ $lamarckiana$.
According to his theory, evolution is a discontinuous process caused by large, sudden, and heritable changes in the genetic material, which he termed as 'mutations'.

(B) When one or two bases are added (inserted) or duplicated in a $DNA$ sequence,the reading frame of the genetic code is altered from the point of insertion onwards. This type of mutation is known as a $Frame-shift$ $insertion$ mutation. Since the genetic code is read in triplets (codons),the addition of one or two bases shifts the entire sequence,leading to the synthesis of a completely different protein or a premature stop codon.

(C) Hugo de Vries, a Dutch botanist, conducted his experiments on the Evening Primrose $(Oenothera \, lamarckiana)$.
Based on his observations of this plant, he proposed the mutation theory, which suggests that evolution is a discontinuous process caused by large, sudden, and heritable changes in the genetic material, known as mutations.

(A) Sickle cell anaemia is caused by a point mutation in the $Hb^A$ gene.
Specifically,a single nucleotide substitution occurs in the $DNA$ sequence where the nucleotide $Adenine$ $(A)$ is replaced by $Thymine$ $(T)$.
This mutation changes the codon $GAG$ to $GTG$ at the sixth position of the $\beta$-globin chain.
Consequently,the amino acid $Glutamic$ $acid$ is replaced by $Valine$ at the sixth position of the hemoglobin protein,leading to the formation of abnormal $Hb^S$ hemoglobin.

(B) According to Hugo de Vries,mutations are large,random,and directionless (saltation),not small and directional. Therefore,option $B$ is incorrect.

(C) In sickle-cell anaemia,a point mutation in the beta globin gene changes the sixth codon from $GAG$ (coding for glutamic acid) to $GUG$ (coding for valine).
This substitution leads to the polymerization of haemoglobin under low oxygen tension,which causes the characteristic sickling of $RBC$s.