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All questions of Principle of Inheritance and Variation for NEET Exam

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Sickle cell anaemia is:
[2009]
  • a)
    caused by a change in a single base pair of DNA
  • b)
    caused by substitution of glutamic acid by valine in the beta globin chain of haemoglobin
  • c)
    characterized by elongated sickle like RBCs with a nucleus
  • d)
    an autosomal linked dominant trait
Correct answer is option 'B'. Can you explain this answer?

Krish Saha answered
Sickle cell anaemia is caused by a change in a single base pair of DNA. Sickle-cell anaemia is the name of a specific form of sickle-cell disease in which there is homozygosity for the mutation that causes HbS. Sickle-cell disease, or sicklecell anaemia (or drepanocytosis), is a life-long blood disorder characterized by red blood cells that assume an abnormal, rigid, sickle shape. Sickling decreases the cells flexibility and results in a risk of various complications. ‘

 Fruit colour in squash in an example of:          [2014]
  • a)
    Recessive epistasis
  • b)
    Dominant epistasis
  • c)
    Complementary genes
  • d)
    Inhibitory genes 
Correct answer is option 'B'. Can you explain this answer?

Raghav Khanna answered
(b) Epistasis is the phenomenon of suppression of phenotypic expression of gene by a nonallelic gene which shows its own effect. A dominant epistatic allele suppresses the  expression ofa nonallelic gene whether the latter is dominant or recessive. For example, fruit colour of Summer Squash (Cucurbita pepo) is governed by a gene which pruduces yellow colour in dominant state (Y-) and green colour in recessive state (yy). 

Which one of the following conditions in humans. is correctly matched with its chromosomal abnormality/linkage?
[2008]
  • a)
    Klinefelters syndrome-44 autosomes + XXY
  • b)
    Colour blindness - Y-linked
  • c)
    Erythroblastosis foetalis - X-linked
  • d)
    Downs syndrome - 44 autosomes + XO 
Correct answer is option 'A'. Can you explain this answer?

Mahi Shah answered
Klinefelter's syndrome is a genetic disorder affecting men in which an individual gains an extra X chromosome, so that the usual Karyotype of XY is replaced by one of XXY. Symptoms of  Klinefelter's syndrome  named after us physician H.P. Klinefelter, include female characteristics (such as breast enlargement). 

Study the pedigree chart given below: What does it show?
[2009]
  • a)
    Inheritance of a condition like phenylketonuria as an autosomal recessive trait
  • b)
    The pedigree chart is wrong as this is not possible
  • c)
    Inheritance of a recessive sex - linked disease like haemophilia
  • d)
    Inheritance of a sex -linked inborn error of metabolism like phenylketonuria
Correct answer is option 'A'. Can you explain this answer?

Ishani Nambiar answered
The chart shows the inheritance of a condition like phenylketonuria as an autosomal recessive trait. Parents’ needs to be heterozygous as two of their children are known to be sufferer of the disease. It cannot be recessive sex linked inheritance because then the male parent would also be sufferer.

A man whose father was colour blind marries a woman who had a colour blind mother and normal father. What percentage of male children of this couple will be colour blind?      [2013]
  • a)
    25%
  • b)
    0%
  • c)
    50%
  • d)
    75% 
Correct answer is option 'C'. Can you explain this answer?

Shivani Rane answered
As color blindness is an autosomal recessive genetic disorder, for it is present at X -chromosome. Thus, according to the situation given in the question, a man whose father was color blind (will be, i.e, XY normal) marries a woman whose mother was color blind and father was normal (i.e, this woman will be a carrier) according to the cross given in the first figure.
Thus, when marriage will happen between a normal man and a carrier woman, in that case, the percentage of a male child to be colorblind is 25% (this can be easily observed from the second figure).So, the correct answer is '50%'.
 

Which of the following statements are correct about Klinefelter’s Syndrome?      (NEET 2023)
A. This disorder was first described by Langdon Down (1866).
B. Such an individual has overall masculine development. However, the feminine developement is also expressed.
C. The affected individual is short statured.
D. Physical, psychomotor and mental development is retarded.
E. Such individuals are sterile.
Choose the correct answer from the options given below:
  • a)
    A and B only
  • b)
    C and D only
  • c)
    B and E only
  • d)
    A and E only
Correct answer is option 'C'. Can you explain this answer?

Top Rankers answered
B. Such an individual has overall masculine development. However, the feminine development is also expressed. People with Klinefelter syndrome are male (XY), but they often have certain physical characteristics that may be typically associated with female development, such as wider hips, less body hair, and sometimes breast tissue development.
E. Such individuals are sterile. Often, individuals with Klinefelter syndrome produce little to no sperm and are therefore usually infertile. However, there are cases where fertility treatments can help some men with Klinefelter syndrome to father children.
For the other options :
A. This disorder was first described by Langdon Down (1866). This is incorrect. Klinefelter's syndrome was first described by Dr. Harry Klinefelter in the 1940s, not by Langdon Down.
C. The affected individual is short statured. This is incorrect. In fact, individuals with Klinefelter's syndrome are often taller than average.
D. Physical, psychomotor and mental development is retarded. This is also incorrect. While individuals with Klinefelter syndrome may have some learning difficulties or delays, particularly with language and speech, it is not accurate or appropriate to say that their physical, psychomotor, and mental development is "retarded". They may face some challenges, but with support they can lead healthy, productive lives.

A cell at telophase stage is observed by a student in a plant brought from the field. He tells his teacher that this cell is not like other cells at telophase stage. There is no formation of cell plate and thus the cell is containing more number of chromosomes as compared to other dividing cells. This would result in          [2016]
  • a)
    Aneuploidy
  • b)
    Polyploidy
  • c)
    Somaclonal variation
  • d)
    Polyteny 
Correct answer is option 'B'. Can you explain this answer?

Sushant Goyal answered
(b) This phenomenon is known as Polyploidy, wherein the cells contain more than two paired (homologous) sets of chromosomes. Polyploidy is often seen in the case of plants. The major cause of polyploidy is the non - disjunction of sister chromatids during meiotic recombination. This condition is actually useful in development of new crop varieties. 

The genotype of a plant showing the dominant phenotype can be determined by :
[2010]
  • a)
    test cross
  • b)
    dihybrid cross
  • c)
    pedigree analysis
  • d)
    back cross
Correct answer is option 'A'. Can you explain this answer?

Pankaj Banerjee answered
Test cross is the cross of an individual with an individual having recessive phenotype. It is used to determine the genotype of a plant showing the dominant phenotype, that means to determine whether the individual exhibiting dominating characters are homozygous or heterozygous.

Which of the following most appropriately describes haemophilia ?                      [2016]
  • a)
    Recessive gene disorder
  • b)
    X - linked recessive gene disorder
  • c)
    Chromosomal disorder
  • d)
    Dominant gene disorder 
Correct answer is option 'B'. Can you explain this answer?

Yash Saha answered
(b) Hemophilia A and hemophilia B are inherited in an X-linked recessive pattern. The genes associated with these conditions are located on the X chromosome, which is one of the two sex chromosomes. In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), a mutation would have to occur in both copies of the gene to cause the disorder. Because it is unlikely that females will have two altered copies of this gene, it is very rare for females to have hemophilia. A characteristic of X-linked inheritance is that fathers cannot pass Xlinked traits to their sons.

Experimental verification of the chromosomal theory of inheritance was done by:   [2020]
  • a)
    Boveri
  • b)
    Morgan
  • c)
    Mendel
  • d)
    Sutton
Correct answer is option 'B'. Can you explain this answer?

Jyoti Sengupta answered
Thomas Hunt Morgan, who studied fruit flies, provided the first strong confirmation of the chromosome theory. “Morgan discovered a mutation that affected fly eye color. The chromosome theory of inheritance states that genes are found at specific locations on chromosomes, and that the behavior of chromosomes during meiosis can explain Mendel's laws of inheritance.

 Broad palm with single palm crease is visible in a person suffering from-      (NEET 2023)
  • a)
    Down’s Syndrome
  • b)
    Turner’s Syndrome
  • c)
    Klinefelter’s Syndrome
  • d)
    Thalassemia
Correct answer is option 'A'. Can you explain this answer?

EduRev NEET answered
A broad palm with a single palmar crease, also known as a "simian crease," is often associated with Down's Syndrome. Down's Syndrome is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is characterized by certain physical features, including a flat facial profile, an upward slant to the eyes, and a single palmar crease.
So, the correct answer is : Option D : Down's syndrome.

Conditions of a karyotype 2n +1, 2n –1 and  2n + 2, 2n – 2 are called:
  • a)
    Aneuploidy
  • b)
    Polyploidy
  • c)
    Allopolyploidy 
  • d)
    Monosomy
Correct answer is option 'A'. Can you explain this answer?

Raza Great answered
Failure of segregation of chromatids during cell division cycle results in the gain or loss of a chromosome called aneuploidy. Aneuploidy arises due to the non-disjunction of the homologous chromosome.

Aneuploidy is of four types:

Monosomy = 2n–1

Nullisomy =2n–2

Trisomy = 2n+1

Tetrasomy =2n+2

Autopolyploidy is an additional set of chromosomes, which may be from a parent or identical parental species.

Polyploids in which there are more than two chromosome sets. It is by 3n (triploid), 4n (tetraploid), 5n (pentaploid).

If a colour blind female marries a man whose mother was also colour blind, what are the chances of her progeny having colour blindness? (NEET 2022)
  • a)
    25%
  • b)
    50%
  • c)
    75%
  • d)
    100%      
Correct answer is option 'D'. Can you explain this answer?

Akshita Tiwari answered
Understanding Color Blindness Genetics
Color blindness, particularly red-green color blindness, is a sex-linked recessive trait located on the X chromosome. To understand the inheritance pattern, let’s analyze the genetic makeup of the individuals involved.
Genetic Makeup of Parents
- A color-blind female has the genotype XcXc (both X chromosomes carry the color blindness allele).
- The man, whose mother was color blind, could either be XcY (color-blind) or XY (normal vision). Since his mother was color blind, he must carry the Xc chromosome, making him XcY.
Possible Combinations of Offspring
When these two individuals reproduce, the possible combinations for their children can be outlined as follows:
1. Female offspring (XX):
- From the mother (Xc): Xc
- From the father (Xc): Xc
- Resulting genotype: XcXc (color blind)
2. Male offspring (XY):
- From the mother (Xc): Xc
- From the father (Y): Y
- Resulting genotype: XcY (color blind)
Progeny Outcomes
Based on the combinations:
- All female offspring will be XcXc (100% color blind).
- All male offspring will be XcY (100% color blind).
Thus, every child, regardless of gender, will have color blindness.
Conclusion
Given this genetic analysis, the probability that any child from this union will have color blindness is 100%.
Thus, the correct answer is option 'D' (100%).

In a plant, black seed color (BB/Bb) is dominant over white seed color (bb). In order to find out the genotype of the black seed plant, with which of the following genotype will you cross it? (NEET 2024)
  • a)
    BB
  • b)
    bb
  • c)
    Bb
  • d)
    BB/Bb
Correct answer is option 'B'. Can you explain this answer?

Mohit Rajpoot answered
To determine the genotype of a black seed plant that could either be homozygous dominant (BB) or heterozygous (Bb), you need to perform a test cross. A test cross involves crossing the individual in question with a homozygous recessive individual. In this scenario, that would be a plant with white seed color, or genotype bb.
A test cross is used because it can reveal whether the black seed plant carries the recessive b allele. When crossed with a homozygous recessive (bb) plant:
By observing the seed colors of the offspring, you can determine whether the black seed plant was homozygous dominant or heterozygous. If any white seeds appear among the offspring, the black seed plant must be heterozygous (Bb). If no white seeds appear, the black seed plant is likely homozygous dominant (BB).
Therefore, the correct option for crossing to determine the genotype of the black seed plant is: Option B bb

Which one of the following can be explained on the basis of Mendel's Law of Dominance?     (NEET 2024)
A. Out of one pair of factors one is dominant and the other is recessive.
B. Alleles do not show any expression and both the characters appear as such in F2 generation.
C. Factors occur in pairs in normal diploid plants.
D. The discrete unit controlling a particular character is called factor.
E. The expression of only one of the parental characters is found in a monohybrid cross.
Choose the correct answer from the options given below:
  • a)
    A, B and C only
  • b)
    A, C, D and E only
  • c)
    B, C and D only
  • d)
    A, B, C, D and E
Correct answer is option 'B'. Can you explain this answer?

Infinity Academy answered
The correct answer is: Option B: A, C, D and E only Explanation:
Mendel's Law of Dominance states that in a heterozygote, the dominant allele will mask the expression of the recessive allele. Let's analyze the options:
A. Out of one pair of factors one is dominant and the other is recessive: This is the core principle of Mendel's Law of Dominance.
C. Factors occur in pairs in normal diploid plants: This is a fundamental concept in genetics, as diploid organisms have two copies of each chromosome, thus two copies of each gene (factors).
D. The discrete unit controlling a particular character is called factor: Mendel used the term "factor" to describe what we now know as genes.
E. The expression of only one of the parental characters is found in a monohybrid cross: This is a direct consequence of the law of dominance, where the dominant trait masks the expression of the recessive trait in the F1 generation of a monohybrid cross.
Option B is incorrect:
B. Alleles do not show any expression and both the characters appear as such in F2 generation: This statement is incorrect. While the recessive allele is not expressed in the F1 generation, it reappears in the F2 generation in a 3:1 ratio (dominant:recessive). This is due to the Law of Segregation, not the Law of Dominance.

If two persons with ‘AB’ blood group marry and have sufficiently large number of children these children could be classified as ‘A’ blood group: ‘AB’ blood group: ‘B’ blood group in 1 : 2 : 1 ratio. Modern technique of protein electrophoresis reveals presence of both ‘A’ and ‘B’ type proteins in ‘AB’ blood group individuals. This is an example of :              
[NEET 2013]
  • a)
    incomplete dominance
  • b)
    Partial dominance
  • c)
    Complete cominance
  • d)
    Codominance
Correct answer is option 'D'. Can you explain this answer?

Mahi Shah answered
ABO blood group system in human beings is an example of codominant, dominant recessive and multiple alletes. Blood groups are controlled by the gene I located on 9th chromosome that has 3 multiple alleles, out of which any two are found in a person. In codominance both gene express it self completely.

Which one of the following can not be explained on the basis of Mendel’s Law of Dominance?
[2010]
  • a)
    The discrete unit controlling a particular character is called a factor
  • b)
    Out of one pair of factors one is dominant, and the other recessive
  • c)
    Alleles do not show any blending and both the characters recover as such in F2 generation.
  • d)
    Factors occur in pairs
Correct answer is option 'C'. Can you explain this answer?

Shivani Rane answered
According to Mendel’s law of Dominance, out of two contrasting allelomorphic factors only one expresses itself in an individual. The factor that expresses itself is called dominant while the other which has not shown its effect in the heterozygous individual is termed as recessive. The option (c) in the given question cannot be explain-ed on the basis of law of dominance. It can only be explained on the basis of Mendel’s Law of independent assortment, according to which in a dihybrid cross, the two alleles of each character assort independently of the alleles of other character and separate at the time of gamete formation.

The frequency of recombination between gene present on the same chromosome as a measure of the distance between genes was explained by    [2019]
  • a)
    Sutton Boveri
  • b)
    T.H. Morgan
  • c)
    Gregor J. Mendel
  • d)
    Alfred Sturtevant
Correct answer is option 'D'. Can you explain this answer?

Gaurav Kumar answered
T.H. Morgan coined the term linkage to describe the physical association of genes on chromosome and term recombination to describe the generation of noil-parental gene combinations. Alfred Sturtevant used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes.

A normal girl, whose mother is haemophilic marries a male with no ancestral history of haemophilia. What will be the possible phenotypes of the offspring?        (NEET 2022 Phase 2)
(a) Haemophilic son and haemophilic daughter.
(b) Haemophilic son and carrier daughter.
(c) Normal daughter and normal son.
(d) Normal son and haemophilic daughter.
Choose the most appropriate answer from the options given below:
  • a)
    (b) and (d) only
  • b)
    (a) and (b) only
  • c)
    (b) and (c) only
  • d)
    (a) and (d) only
Correct answer is option 'C'. Can you explain this answer?

Dhruba Patel answered
Understanding Haemophilia Inheritance
Haemophilia is an X-linked recessive disorder, meaning that the gene responsible for haemophilia is located on the X chromosome. The inheritance pattern is crucial in predicting the phenotypes of offspring from a normal female carrier and a normal male.
Genotype of the Parents
- The mother is a carrier for haemophilia, so her genotype is XhX (where Xh represents the X chromosome with the haemophilia allele).
- The father is normal, so his genotype is XY.
Possible Offspring Genotypes
1. Male Offspring (XY)
- Inherit Y from father and either X from mother:
- XhY (haemophilic son)
- XY (normal son)
2. Female Offspring (XX)
- Inherit X from father and either X from mother:
- XhX (carrier daughter)
- XX (normal daughter)
Possible Phenotypes
Based on the combinations above, the possible phenotypes for the offspring are:
- Haemophilic Son: Inherits Xh from the mother.
- Carrier Daughter: Inherits Xh from the mother.
- Normal Son: Inherits X from the mother.
- Normal Daughter: Inherits X from the mother.
Evaluating the Options
- Option (a): Haemophilic son and haemophilic daughter - Not possible (only sons can be haemophilic, daughters can be carriers or normal).
- Option (b): Haemophilic son and carrier daughter - Possible.
- Option (c): Normal daughter and normal son - Possible.
- Option (d): Normal son and haemophilic daughter - Not possible.
Conclusion
The correct answer is option C (b) and (c) only, as these combinations accurately reflect the potential phenotypes of the offspring based on the inheritance of haemophilia.

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason(R).     (NEET 2022)
Assertion (A): Mendel's law of Independent assortment does not hold good for the genes that are located closely on the same chromosome.
Reason (R): Closely located genes assort independently. In the light of the above statements, choose the correct answer from the options given below:
  • a)
    Both (A) and (R) are correct but (R) is not the correct explanation of (A)
  • b)
    (A) is correct but (R) is not correct
  • c)
    (A) is not correct but (R) is correct
  • d)
    Both (A) and (R) are correct and (R) is the correct explanation of (A)
Correct answer is option 'B'. Can you explain this answer?

EduRev NEET answered
Closely located genes do not show independent assortment. Mendel's law of independent assortment holds good for those genes which are located on different chromosomes.

What is the expected percentage of F2 progeny with yellow and inflated pod in dihybrid cross experiment involving pea plants with green coloured, inflated pod and yellow coloured constricted pod?    (NEET 2022 Phase 2)
  • a)
    9%
  • b)
    100%
  • c)
    56.25%
  • d)
    18.75%
Correct answer is option 'D'. Can you explain this answer?

Sahil Goyal answered
Understanding the Dihybrid Cross
In a dihybrid cross involving pea plants, we are looking at two traits: pod color (yellow vs. green) and pod shape (inflated vs. constricted). In this scenario:
- Green color (G) is dominant over yellow color (g).
- Inflated shape (I) is dominant over constricted shape (i).
The parental genotypes can be represented as:
- Parent 1: Homozygous green inflated (GGII)
- Parent 2: Homozygous yellow constricted (ggii)
F1 Generation
Crossing these parents produces the F1 generation:
- All offspring will be heterozygous (GgIi) exhibiting green and inflated pods due to the dominance of both traits.
F2 Generation
When F1 plants are self-fertilized (GgIi x GgIi), the F2 generation is produced. We can analyze the phenotypic ratio using a Punnett square or by applying the independent assortment principle. The expected phenotypic ratio for a dihybrid cross is:
- 9:3:3:1 ratio
This translates to:
- 9 green inflated
- 3 green constricted
- 3 yellow inflated
- 1 yellow constricted
Calculating the Expected Phenotype
To find the percentage of F2 progeny with yellow and inflated pods, we look at the 3 yellow inflated from the ratio:
- Total phenotypes = 16 (9 + 3 + 3 + 1)
- Yellow inflated = 3 out of 16
Final Calculation
Thus, the percentage of yellow inflated pods in the F2 generation is:
- (3/16) * 100 = 18.75%
Therefore, the expected percentage of F2 progeny with yellow and inflated pods is 18.75%.
The correct answer is option D.

A test cross is carried out to
[2012M]
  • a)
    determine the genotype of a plant at F2.
  • b)
    predict whether two traits are linked.
  • c)
    assess the number of alleles of a gene.
  • d)
    determine whether two species or varieties will breed successfully.
Correct answer is option 'A'. Can you explain this answer?

Arpita Tiwari answered
A test cross, first introduced by Gregor Mendel, is used to determine if an individual exhibiting a dominant trait is homozygous or heterozygous for that trait. It takes place between F1 - Generation and recessive parent.

Which of the following occurs due to the presence of autosome linked dominant trait?     (NEET 2022)
  • a)
    Haemophilia 
  • b)
    Thalessemia 
  • c)
    Sickle cell anaemia 
  • d)
    Myotonic dystrophy
Correct answer is option 'D'. Can you explain this answer?

Prasenjit Khanna answered
Understanding Autosomal Dominant Traits
Autosomal dominant traits are genetic traits that manifest even when only one copy of the mutated gene is present. They are typically inherited from one affected parent and can appear in every generation.
Myotonic Dystrophy as an Autosomal Dominant Trait
Myotonic dystrophy is a prime example of an autosomal dominant disorder. Here’s why it fits this category:
  • Inheritance Pattern: If one parent has the myotonic dystrophy gene, there is a 50% chance of passing it to each child, regardless of the child's gender.
  • Gene Mutation: The disorder is caused by a mutation in the DMPK gene, leading to muscle weakness and myotonia (difficulty relaxing muscles).
  • Phenotypic Expression: Symptoms can vary significantly, from mild to severe, but they will appear if the mutated gene is inherited.

Why Other Options Are Incorrect
  • Haemophilia: This is an X-linked recessive disorder, primarily affecting males, and does not follow an autosomal dominant inheritance pattern.
  • Thalassemia: This condition is typically inherited in an autosomal recessive manner, requiring two copies of the mutated gene for the disease to manifest.
  • Sickle Cell Anemia: Similar to thalassemia, it is also an autosomal recessive disorder, requiring both parents to pass on the mutated allele for the disease to occur.

Conclusion
In summary, among the given options, only myotonic dystrophy is an autosomal linked dominant trait, making option 'D' the correct answer. Understanding these inheritance patterns is crucial for genetics and medical studies.

As per ABO blood grouping system, the blood group of father is B+ , mother is A+ and child is O+ . Their respective genotype can be
A. IBi / IAi / ii  
B. IBIB/ IAIA/ ii
C. IAIB/ iIA/ IBi  
D. IAi/IBi/IAi  
E. iIB / iIA / IAIB
Choose the most appropriate answer from the options given below :       (NEET 2024)
  • a)
    A only
  • b)
    B only
  • c)
    C & B only
  • d)
    D & E only
Correct answer is option 'A'. Can you explain this answer?

Manisha Kulkarni answered
Understanding ABO Blood Grouping System
The ABO blood grouping system is determined by the presence of antigens on the surface of red blood cells. The main alleles are A (IA), B (IB), and O (i). Each person has two alleles, one inherited from each parent, which define their blood type.
Parental Blood Groups and Genotypes
- Father's Blood Group: B+
- Possible Genotypes: IBIB or IBi
- Mother's Blood Group: A+
- Possible Genotypes: IAIA or IAi
Child's Blood Group: O+
For the child to have blood type O (genotype ii), both parents must contribute an O allele (i).
Analyzing the Genotypes
1. Father (B+) can either be IBIB or IBi.
- If he is IBIB, he cannot contribute an O allele.
- If he is IBi, he can contribute an i allele.
2. Mother (A+) can either be IAIA or IAi.
- If she is IAIA, she cannot contribute an O allele.
- If she is IAi, she can contribute an i allele.
Thus, the only viable combination for the child to be type O (ii) is:
- Father: IBi (carrying i)
- Mother: IAi (carrying i)
Conclusion on Options
The only option that fits this analysis is:
- Option A: IAi (mother), IBi (father), ii (child)
This confirms that the genotypes align correctly for the child's blood type to be O+. Other options either include incorrect genotypes or do not account for the necessity of both parents contributing an i allele.
Final Answer
The correct answer is option A only.

If a geneticist uses the blind approach for sequencing the whole genome of an organism, followed by assignment of function to different segments, the methodology adopted by him is called as:     (NEET 2022)
  • a)
    Gene mapping
  • b)
    Expressed sequence tags
  • c)
    Bioinformatics
  • d)
    Sequence annotation
Correct answer is option 'D'. Can you explain this answer?

EduRev NEET answered
In sequence annotation, the whole set of genome containing all coding and non-coding sequences is sequenced and the functions are assigned to different segments. It could be used for marking specific features in a DNA, RNA or protein sequence with descriptive information about structure or function. It helps in describing regions or sites of interest in the protein sequence, such as enzyme active sites, secondary structure or other characteristics reported in the cited references.

Which one of the following is a wrong statement regarding mutations?
[2012M]
  • a)
    Deletion and insertion of base pairs cause frame-shift mutations.
  • b)
    Cancer cells commonly show chromosomal aberrations.
  • c)
    UV and Gamma rays are mutagens.
  • d)
    Change in a single base pair of DNA does not cause mutation.
Correct answer is option 'D'. Can you explain this answer?

Ishita Rane answered
Change in a single base pair of DNA does not cause mutation:
Mutation is a change in the DNA sequence that can lead to genetic variations. While it is true that mutations can be caused by a variety of factors, including UV and Gamma rays, deletion and insertion of base pairs, and chromosomal aberrations, it is incorrect to say that a change in a single base pair of DNA does not cause a mutation.

Explanation:
- A change in a single base pair of DNA is known as a point mutation.
- Point mutations can have various effects on the resulting protein encoded by the DNA sequence.
- For example, a point mutation can lead to a silent mutation (no change in the amino acid sequence), a missense mutation (change in one amino acid), or a nonsense mutation (introduction of a premature stop codon).
- These changes can ultimately affect the structure and function of the protein, leading to potential phenotypic changes.
- Therefore, it is important to recognize that even a small change in a single base pair of DNA can indeed cause a mutation.

The recombination frequency between the genes a & c 5&, b & c is 15%, b & d is 9%, a & b is 20%, c & d is 25% and a & d is 29%. What will be the sequence of these genes on a linear chromosome?   (NEET 2022)
  • a)
    a, d, b, c
  • b)
    d, b, a, c
  • c)
    a, b, c, d
  • d)
    a, c, b, d      
Correct answer is option 'D'. Can you explain this answer?

Nishtha Nair answered
Understanding Recombination Frequencies
The recombination frequency indicates the distance between genes on a chromosome. A higher percentage suggests genes are farther apart, while a lower percentage indicates they are closer together.
Given Recombination Frequencies
- a & c: 5%
- b & c: 15%
- b & d: 9%
- a & b: 20%
- c & d: 25%
- a & d: 29%
Analyzing the Data
1. Closest Genes:
- The smallest recombination frequency is between a & c (5%), indicating they are adjacent.
2. Next Closest:
- The next smallest frequency is between b & d (9%). Since a & c are already next to each other, we should place b and d nearby.
3. Placing b:
- a & b (20%) suggests that b is also close to a.
- With 5% between a & c, we can place them as: a - c.
4. Placing d:
- Since a & d have a frequency of 29%, we can place d after b, making the sequence: a - c - b - d.
5. Final Sequence:
- The sequence is a - c - b - d.
Conclusion
After evaluating the recombination frequencies, the correct sequence of genes on a linear chromosome is option 'D': a, c, b, d. This arrangement aligns with the provided recombination data.

Point mutation involves:
[2009]
  • a)
    change in single base pair
  • b)
    duplication
  • c)
    deletion
  • d)
    insertion
Correct answer is option 'A'. Can you explain this answer?

Mahi Shah answered
A point mutation is a simple change in one base of the gene sequence. This is equivalent to changing one letter in a sentence, such as this example, where we change the ‘e’ in cat to an ‘h’: Original: The fat cat ate the wee rat. Point Mutation: The fat hat ate the wee rat.

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