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Principles of Inheritance and Variation — NEET MCQs with answers
Mendel's hybridisation experiments on garden peas (1856-1863) established the laws of inheritance - dominance, segregation and independent assortment - and were the first to apply statistical analysis and mathematical logic to biology. The chapter extends Mendelian genetics to incomplete dominance, co-dominance (ABO blood groups), polygenic inheritance, pleiotropy, sex determination (XO, XY, ZW, haplodiploidy), mutation, and Mendelian and chromosomal disorders. The chromosomal theory of inheritance (Sutton and Boveri) was experimentally verified by Morgan, whose work on Drosophila introduced linkage and recombination.
Topics in this chapter
- 4.1 Mendel's Laws of Inheritance
- 4.2 Inheritance of One Gene
- 4.3 Inheritance of Two Genes
- 4.4 Polygenic Inheritance
- 4.5 Pleiotropy
- 4.6 Sex Determination
- 4.7 Mutation
- 4.8 Genetic Disorders
Free practice questions
When Mendel self-pollinated the tall F1 pea plants, the F2 generation showed tall and dwarf plants in what phenotypic ratio?
- A. 1:1
- B. 1:2:1
- C. 9:3:3:1
- D. 3:1
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Answer: D — In F2, 3/4th of the plants were tall and 1/4th were dwarf, giving a 3:1 phenotypic ratio. The traits did not blend.
NCERT Class 12 Biology · Ch 4 · 4.2 Inheritance of One Gene
Which one of the following results in an alteration in the chromosome rather than a point change?
- A. A single nucleotide substitution
- B. GAG to GUG change at one codon
- C. Change of one base pair
- D. Duplication of a DNA segment
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Answer: D — NCERT: loss (deletion) or gain (insertion/duplication) of a DNA segment alters chromosomes; these are distinct from a single base pair point mutation.
NCERT Class 12 Biology · Ch 4 · 4.7 Mutation
Why can a male honey bee (drone) not have sons?
- A. It is sterile and produces no sperm
- B. It always dies before mating
- C. It has no father and, being haploid, cannot pass through a son line
- D. Its sperm are produced by meiosis
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Answer: C — NCERT: The drone develops from an unfertilised egg and produces sperm by mitosis; it does not have a father and cannot have sons (its sperm fertilises eggs that become females, and its unfertilised-egg descendants trace through daughters).
NCERT Class 12 Biology · Ch 4 · 4.6 Sex Determination · 4.6.2
Beta thalassemia is controlled by a single gene HBB located on:
- A. Chromosome 11 of each parent
- B. Chromosome 6 of each parent
- C. The Y chromosome
- D. Chromosome 16 of each parent
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Answer: A — NCERT states beta thalassemia is controlled by a single gene HBB on chromosome 11 of each parent, occurring due to mutation of one or both genes.
NCERT Class 12 Biology · Ch 4 · 4.8.2 Mendelian Disorders (Thalassemia)
Which Mendelian law was proposed on the basis of the dihybrid cross?
- A. Law of Dominance
- B. Law of Independent Assortment
- C. Law of Purity of Gametes
- D. Law of Segregation
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Answer: B — Section 4.3.1 states that based on observations from dihybrid crosses, Mendel proposed the Law of Independent Assortment.
NCERT Class 12 Biology · Ch 4 · 4.3.1 Law of Independent Assortment
Which human disease is given by NCERT as an example of pleiotropy?
- A. Phenylketonuria
- B. Thalassemia
- C. Down's syndrome
- D. Colour blindness
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Answer: A — NCERT cites phenylketonuria, occurring in humans, as an example of pleiotropy.
NCERT Class 12 Biology · Ch 4 · 4.5 Pleiotropy
How many pairs of contrasting characters in the garden pea did Mendel study?
- A. Six
- B. Seven
- C. Five
- D. Nine
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Answer: B — Mendel selected 14 true-breeding varieties as pairs — seven pairs of contrasting traits (stem height, flower colour, flower position, pod shape, pod colour, seed shape, seed colour).
NCERT Class 12 Biology · Ch 4 · 4.1 Mendel's Laws of Inheritance
In the NCERT skin-colour model, a genotype carrying three dominant alleles and three recessive alleles would have:
- A. An intermediate skin colour
- B. No pigmentation at all
- C. The darkest skin colour
- D. The lightest skin colour
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Answer: A — NCERT states that, as expected, the genotype with three dominant alleles and three recessive alleles will have an intermediate skin colour.
NCERT Class 12 Biology · Ch 4 · 4.4 Polygenic Inheritance
The phenotype of an organism can change as a result of mutation because mutation alters the:
- A. DNA sequence (genotype)
- B. Only the diet
- C. Only the temperature
- D. Only the environment
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Answer: A — NCERT: mutation results in alteration of DNA sequences and consequently changes in genotype and phenotype.
NCERT Class 12 Biology · Ch 4 · 4.7 Mutation
In a species where the female is ZW and the male is ZZ, the sex of the offspring is determined by:
- A. environmental temperature
- B. the number of autosomes in the sperm
- C. the type of egg (Z- or W-bearing) produced by the female
- D. the type of sperm produced by the male
Show answer
Answer: C — NCERT: In birds the female (ZW) produces two types of gametes (Z or W), so the female (the egg) determines the sex — female heterogamety.
NCERT Class 12 Biology · Ch 4 · 4.6 Sex Determination
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