Working with the garden pea (Pisum sativum), Gregor Mendel crossed true-breeding plants differing in a single contrasting trait — round versus wrinkled seeds, tall versus dwarf stems — and found the F1 generation always resembled only one parent, never a blend. He called the trait that appeared dominant and the one that disappeared recessive — the law of dominance. Each trait, he proposed, i
Principles of Inheritance and Variation
Class 1233 previous-year questions from this chapter every option and the correct answer, free · where the marks are
1. Mendel's laws and deviations
Exam focus: Don't let "both parental traits show up" collapse into "blended appearance": incomplete dominance genuinely blends into an intermediate phenotype (pink Mirabilis), while codominance keeps both parental phenotypes fully and separately visible at once (AB blood group) — NEET options trade directly on that difference.
Principles of Inheritance and Variation — Full Chapter
Vedantu Biotonic for NEET
Covers Mendel's three laws and the deviations (incomplete dominance, codominance, multiple alleles, pleiotropy) as part of the whole chapter, which continues into sex determination, mutation and genetic disorders — the next subtopic below.
ZoologyNEET 2025show ▾Genes R and Y follow independent assortment. If RRYY produces round yellow seeds and rryy produces wrinkled green seeds, what will be the phenotypic ratio of the generation?
- A.Phenotypic ratio 1 : 2 : 1
- B.Phenotypic ratio 3 : 1
- C.Phenotypic ratio 9 : 3 : 3 : 1✓
- D.Phenotypic ratio 9 : 7
Solution
Independent assortment of two genes in a dihybrid cross gives the classical 9 : 3 : 3 : 1 phenotypic ratio in the round yellow : round green : wrinkled yellow : wrinkled green).
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Save for spaced revision (free account)BotanyNEET 2025show ▾What is the pattern of inheritance for a polygenic trait?
- A.Mendelian inheritance pattern
- B.Non-Mendelian inheritance pattern✓
- C.Autosomal dominant pattern
- D.X-linked recessive inheritance pattern
Solution
Polygenic traits such as skin colour and height are controlled by several genes with additive effects and show continuous variation — a non-Mendelian pattern.
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Save for spaced revision (free account)BotanyNEET 2024show ▾Match List I with List II.
List I List II A. Two or more alternative forms of a gene I. Back cross B. Cross of progeny with homozygous recessive parent II. Ploidy C. Cross of progeny with any of the parents III. Allele D. Number of chromosome sets in a plant IV. Test cross
Choose the correct answer from the options given below:
- A.A-II, B-I, C-III, D-IV
- B.A-III, B-IV, C-I, D-II✓
- C.A-IV, B-III, C-II, D-I
- D.A-I, B-II, C-III, D-IV
Solution
Alternative forms of a gene are alleles (III). Crossing with the homozygous recessive parent is a test cross (IV); with either parent, a back cross (I). The number of chromosome sets is ploidy (II).
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Save for spaced revision (free account)BotanyNEET 2024show ▾In a plant, black seed colour (BB/Bb) is dominant over white seed colour (bb). In order to find out the genotype of a black-seeded plant, with which of the following genotypes will you cross it?
- A.bb✓
- B.Bb
- C.BB/Bb
- D.BB
Solution
To reveal a dominant plant's genotype, cross it with the homozygous recessive (bb) — a test cross. Any white-seeded progeny proves the parent is Bb.
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Save for spaced revision (free account)BotanyNEET 2024show ▾Which of the following can be explained on the basis of Mendel's Law of Dominance?
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 the generation.
C. Factors occur in pairs in normal diploid plants.
D. The discrete unit controlling a particular character is called a 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, C, D and E only✓
- B.B, C and D only
- C.A, B, C, D and E
- D.A, B and C only
Solution
The law of dominance covers: characters are controlled by factors (D); factors occur in pairs (C); in a dissimilar pair one factor is dominant, the other recessive (A); so only one parental character shows in the of a monohybrid cross (E). Statement B describes incomplete/co-dominance, not dominance. So A, C, D and E.
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Save for spaced revision (free account)BotanyNEET 2024show ▾A pink-flowered snapdragon plant was crossed with a red-flowered snapdragon plant. What type of phenotype(s) is/are expected in the progeny?
- A.Red-flowered as well as pink-flowered plants✓
- B.Only pink-flowered plants
- C.Red, pink as well as white-flowered plants
- D.Only red-flowered plants
Solution
Snapdragon flower colour shows incomplete dominance: pink is the heterozygote (Rr). Pink × red (Rr × RR) gives 1 RR : 1 Rr — red and pink plants only, no white.
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Save for spaced revision (free account)ZoologyNEET 2024show ▾As per the ABO blood grouping system, the blood group of the father is B+, the mother is A+ and the child is O+. Their respective genotypes can be:
A. · B. · C. · D. · E.
Choose the most appropriate answer from the options given below:
- A.B only
- B.C & B only
- C.D & E only
- D.A only✓
Solution
An O-group child (ii) must receive an i allele from each parent, so the B⁺ father is and the A⁺ mother . Only set A fits; the other sets give at least one parent no i allele or the child a wrong genotype.
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Save for spaced revision (free account)BotanyNEET 2023show ▾The phenomenon of pleiotropism refers to:
- A.Presence of several alleles of a single gene controlling a single crossover
- B.Presence of two alleles, each of the two genes controlling a single trait
- C.A single gene affecting multiple phenotypic expressions✓
- D.More than two genes affecting a single character
The worked solution is part of a paid pack.
BotanyNEET 2022show ▾Given below are two statements:
Statement I: Mendel studied seven pairs of contrasting traits in pea plants and proposed the Laws of Inheritance.
Statement II: The seven characters examined by Mendel in his experiments on pea plants were seed shape and colour, flower colour, pod shape and colour, flower position and stem height.
In the light of the above statements, choose the correct answer from the options given below:
- A.Statement I is incorrect but Statement II is correct
- B.Both Statement I and Statement II are correct✓
- C.Both Statement I and Statement II are incorrect
- D.Statement I is correct but Statement II is incorrect
The worked solution is part of a paid pack.
BotanyNEET 2021show ▾The production of gametes by the parents, formation of zygotes, the and plants, can be understood from a diagram called:
- A.Bullet square
- B.Punch square
- C.Punnett square✓
- D.Net square
The worked solution is part of a paid pack.
BotanyNEET 2020show ▾How many true-breeding pea plant varieties, similar except in one character with contrasting traits, did Mendel select as pairs?
BotanyNEET 2020show ▾Identify the wrong statement with reference to the gene 'I' that controls ABO blood groups.
- A.The gene (I) has three alleles
- B.A person will have only two of the three alleles
- C.When and are present together, they express the same type of sugar✓
- D.Allele 'i' does not produce any sugar
The worked solution is part of a paid pack.
BotanyNEET 2019show ▾In Antirrhinum (snapdragon), a red flower was crossed with a white flower, and pink flowers were obtained in the generation. When pink flowers were selfed, the generation showed white, red and pink flowers. Choose the INCORRECT statement from the following:
- A.This experiment does not follow the principle of dominance
- B.Pink colour in is due to incomplete dominance
- C.The ratio is (red) : (pink) : (white)
- D.The law of segregation does not apply in this experiment✓
The worked solution is part of a paid pack.
2. Chromosomal theory and linkage
Exam focus: Genes on the same chromosome recombine less often than the 50% independent assortment would predict, and less often still the closer together they sit — the extreme case NCERT names is male Drosophila, where crossing over does not happen at all.
Chromosomal Theory of Inheritance
Competition Wallah
Thorough lecture on the chromosomal theory of inheritance itself; linkage is taught by this same channel/series as a separate follow-up lecture, so linkage coverage here is limited.
BotanyNEET 2023show ▾The frequency of recombination between gene pairs on the same chromosome, as a measure of the distance between genes to map their position on the chromosome, was used for the first time by:
- A.Thomas Hunt Morgan
- B.Sutton and Boveri
- C.Alfred Sturtevant✓
- D.Henking
The worked solution is part of a paid pack.
ZoologyNEET 2022show ▾The recombination frequency between the genes a & c is 5%, b & c is 15%, b & d is 9%, a & b is 20%, c & d is 24% and a & d is 29%. What will be the sequence of these genes on a linear chromosome?
- A.a, c, b, d✓
- B.a, d, b, c
- C.d, b, a, c
- D.a, b, c, d
The worked solution is part of a paid pack.
BotanyNEET 2022show ▾Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Mendel's law of independent assortment does not hold good for 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.(A) is not correct but (R) is correct
- B.Both (A) and (R) are correct and (R) is the correct explanation of (A)
- C.Both (A) and (R) are correct but (R) is not the correct explanation of (A)
- D.(A) is correct but (R) is not correct✓
The worked solution is part of a paid pack.
BotanyNEET 2020show ▾Experimental verification of the chromosomal theory of inheritance was done by:
- A.Mendel
- B.Sutton
- C.Boveri
- D.Morgan✓
The worked solution is part of a paid pack.
BotanyNEET 2019show ▾The shorter and longer arms of a submetacentric chromosome are referred to as:
- A.s-arm and l-arm, respectively
- B.p-arm and q-arm, respectively✓
- C.q-arm and p-arm, respectively
- D.m-arm and n-arm, respectively
The worked solution is part of a paid pack.
BotanyNEET 2019show ▾The frequency of recombination between gene pairs on the same chromosome, as a measure of the distance between genes, was explained by:
- A.T.H. Morgan
- B.Gregor J. Mendel
- C.Alfred Sturtevant✓
- D.Sutton and Boveri
The worked solution is part of a paid pack.
BotanyNEET 2019show ▾What map unit (centimorgan) is adopted in the construction of genetic maps?
- A.A unit of distance between two expressed genes representing 10% cross-over
- B.A unit of distance between two expressed genes representing 100% cross-over
- C.A unit of distance between genes on chromosomes, representing 1% cross-over✓
- D.A unit of distance between genes on chromosomes, representing 50% cross-over
The worked solution is part of a paid pack.
3. Sex determination, mutation, genetic disorders
Exam focus: Don't default to the mammalian pattern: in the ZW system that governs birds (and some fish and moths), it's the female who is heterogametic and determines the offspring's sex — the reverse of the XY system, where that role belongs to the human male.
Sex Determination, Mutation and Genetic Disorders — Chapter Revision
Competition Wallah
A 46-minute revision of the full Principles of Inheritance and Variation chapter; covers sex determination, mutation and genetic disorders at revision pace, bundled with Mendel's laws rather than as a dedicated deep dive.
ZoologyNEET 2025show ▾With the help of the given pedigree, find out the probability for the birth of a child having no disease and being a carrier (has the disease mutation in one allele of the gene) in the generation.
- A.1/4✓
- B.1/2
- C.1/8
- D.Zero
Solution
The pedigree fits X-linked recessive inheritance (affected mother → all daughters carriers; carrier mother → affected son). The cross is carrier female × affected male : offspring (carrier daughter), (affected daughter), (normal son), (affected son), each 1/4. Probability of a disease-free carrier is 1/4.
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Save for spaced revision (free account)ZoologyNEET 2024show ▾Match List I with List II.
List I List II A. Down's syndrome I. 11th chromosome Thalassemia II. X chromosome Thalassemia III. 21st chromosome D. Klinefelter's syndrome IV. 16th chromosome
Choose the correct answer from the options given below:
- A.A-II, B-III, C-IV, D-I
- B.A-III, B-IV, C-I, D-II✓
- C.A-IV, B-I, C-II, D-III
- D.A-I, B-II, C-III, D-IV
Solution
Down's syndrome is trisomy 21 (III). The globin gene is on chromosome 11 (I) and the globin genes on chromosome 16 (IV). Klinefelter's syndrome involves an extra X chromosome (II).
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Save for spaced revision (free account)ZoologyNEET 2023show ▾A broad palm with a single palm crease is visible in a person suffering from:
- A.Down's syndrome✓
- B.Turner's syndrome
- C.Klinefelter's syndrome
- D.Thalassemia
The worked solution is part of a paid pack.
ZoologyNEET 2023show ▾Which one of the following symbols (shown in the figure) represents mating between relatives in human pedigree analysis?
- A.Symbol (1)
- B.Symbol (2)✓
- C.Symbol (3)
- D.Symbol (4)
The worked solution is part of a paid pack.
BotanyNEET 2023show ▾Which of the following statements are correct about Klinefelter's syndrome?
A. This disorder was first described by Langdon Down (1866).
B. Such an individual has overall masculine development; however, feminine development 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
The worked solution is part of a paid pack.
BotanyNEET 2022show ▾Which of the following occurs due to the presence of an autosome-linked dominant trait?
- A.Thalassemia
- B.Sickle cell anaemia
- C.Myotonic dystrophy✓
- D.Haemophilia
The worked solution is part of a paid pack.
ZoologyNEET 2022show ▾If a colour-blind female marries a man whose mother was also colour blind, what are the chances of her progeny having colour blindness?
- A.100%✓
- B.25%
- C.50%
- D.75%
The worked solution is part of a paid pack.
BotanyNEET 2022show ▾XO type of sex determination can be found in:
- A.Monkeys
- B.Drosophila
- C.Birds
- D.Grasshoppers✓
The worked solution is part of a paid pack.
BotanyNEET 2021show ▾Mutations in plant cells can be induced by:
- A.Kinetin
- B.Infrared rays
- C.Gamma rays✓
- D.Zeatin
The worked solution is part of a paid pack.
ZoologyNEET 2021show ▾In a cross between a male and a female, both heterozygous for the sickle cell anaemia gene, what percentage of the progeny will be diseased?
- A.50%
- B.75%
- C.25%✓
- D.100%
The worked solution is part of a paid pack.
BotanyNEET 2020show ▾Select the correct match.
- A.Haemophilia – Y-linked
- B.Phenylketonuria – Autosomal dominant trait
- C.Sickle cell anaemia – Autosomal recessive trait, chromosome-11✓
- D.Thalassemia – X-linked
The worked solution is part of a paid pack.
BotanyNEET 2019show ▾Select the incorrect statement.
- A.Male fruit fly is heterogametic
- B.In male grasshoppers, 50% of sperms have no sex chromosome
- C.In domesticated fowls, the sex of the progeny depends on the type of sperm rather than the egg✓
- D.Human males have one of their sex chromosomes much shorter than the other
The worked solution is part of a paid pack.
BotanyNEET 2019show ▾What is the genetic disorder in which an individual has overall masculine development, gynaecomastia, and is sterile?
- A.Turner's syndrome
- B.Klinefelter's syndrome✓
- C.Edward's syndrome
- D.Down's syndrome
The worked solution is part of a paid pack.