Principles of Inheritance and Variation for Competitive Exams

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Principles of Inheritance and Variation

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Principles of Inheritance and Variation explains how traits are transmitted from one generation to the next and how variations arise among individuals. This category focuses on the laws of inheritance, genetic patterns, and sources of variation, making it suitable for Class 11–12 students, NEET aspirants, and undergraduate learners.

In this section, you will study:

Mendel’s experiments and laws of inheritance
Monohybrid and dihybrid crosses
Incomplete dominance, codominance, and multiple alleles
Chromosomal theory of inheritance
Linkage, recombination, and gene mapping
Sex determination and sex-linked inheritance
Genetic disorders and pedigree analysis
NCERT-based explanations, diagrams, MCQs, and exam-oriented questions

The content is structured to build strong conceptual foundations, improve problem-solving and cross-based questions, and help students perform confidently in school examinations, NEET, and undergraduate assessments.

Develop a clear understanding of inheritance patterns and genetic variation to master one of the most scoring and concept-rich areas of Biology.

Q. In plants, what is the role of the flower in reproduction?

A. Photosynthesis
B. Water absorption
C. Pollination and fertilization
D. Nutrient storage

Solution

The flower is the reproductive structure in flowering plants, facilitating pollination and fertilization to produce seeds.

Correct Answer: C — Pollination and fertilization

Q. In plants, what is the significance of genetic variation?

A. It decreases adaptability
B. It enhances survival and reproduction
C. It leads to uniformity in traits
D. It is irrelevant to evolution

Solution

Genetic variation enhances survival and reproduction by allowing populations to adapt to changing environments.

Correct Answer: B — It enhances survival and reproduction

Q. In plants, what is the term for the physical location of a gene on a chromosome?

A. Allele
B. Locus
C. Phenotype
D. Genotype

Solution

The term 'locus' refers to the specific physical location of a gene on a chromosome.

Correct Answer: B — Locus

Q. What is a phenotype ratio of a dihybrid cross?

A. 1:1
B. 3:1
C. 9:3:3:1
D. 1:2:1

Solution

A dihybrid cross typically results in a 9:3:3:1 phenotypic ratio, representing the combinations of two traits.

Correct Answer: C — 9:3:3:1

Q. What is the expected phenotypic ratio in the offspring of a monohybrid cross between two heterozygous plants?

A. 1:1
B. 3:1
C. 9:3:3:1
D. 1:2:1

Solution

In a monohybrid cross (Aa x Aa), the expected phenotypic ratio of the offspring is 3:1, where 3 exhibit the dominant trait and 1 exhibits the recessive trait.

Correct Answer: B — 3:1

Q. What is the primary function of the process of meiosis in plants?

A. To produce identical daughter cells
B. To generate genetic variation
C. To facilitate photosynthesis
D. To increase plant size

Solution

Meiosis is crucial for sexual reproduction as it reduces the chromosome number by half and introduces genetic variation through recombination.

Correct Answer: B — To generate genetic variation

Q. What is the role of alleles in inheritance?

A. They are the same as genes
B. They are alternative forms of a gene
C. They determine the environment of a plant
D. They are only found in animals

Solution

Alleles are different versions of a gene that can produce variations in traits among individuals.

Correct Answer: B — They are alternative forms of a gene

Q. What is the significance of genetic variation in plant populations?

A. It decreases adaptability
B. It enhances survival and adaptability
C. It leads to uniformity in traits
D. It has no impact on evolution

Solution

Genetic variation is crucial for the adaptability and survival of plant populations, allowing them to respond to environmental changes.

Correct Answer: B — It enhances survival and adaptability

Q. What is the significance of the Law of Segregation in plant genetics?

A. It explains how traits are inherited independently
B. It states that alleles segregate during gamete formation
C. It describes the dominance of certain traits
D. It outlines the process of photosynthesis

Solution

The Law of Segregation states that during gamete formation, the two alleles for a trait segregate from each other, ensuring that offspring receive one allele from each parent.

Correct Answer: B — It states that alleles segregate during gamete formation

Q. What is the term for the observable characteristics of an organism resulting from the interaction of its genotype with the environment?

A. Genotype
B. Phenotype
C. Heredity
D. Mutation

Solution

The phenotype is the set of observable characteristics of an organism, influenced by both genetic and environmental factors.

Correct Answer: B — Phenotype

Q. What term describes the genetic makeup of an organism?

A. Phenotype
B. Genotype
C. Allele
D. Chromosome

Solution

The genotype refers to the specific genetic constitution of an organism, while the phenotype is the observable expression of that genotype.

Correct Answer: B — Genotype

Q. What type of inheritance pattern is observed in incomplete dominance?

A. One allele completely masks another
B. Both alleles are expressed equally
C. One allele is dominant over the other
D. Traits blend together in the phenotype

Solution

In incomplete dominance, the phenotype of heterozygous individuals is a blend of the two parental traits.

Correct Answer: D — Traits blend together in the phenotype

Q. Which of the following best describes a recessive allele?

A. It is always expressed in the phenotype
B. It can only be expressed in a homozygous condition
C. It is more common than dominant alleles
D. It masks the effect of dominant alleles

Solution

A recessive allele is only expressed in the phenotype when an individual has two copies of that allele (homozygous condition).

Correct Answer: B — It can only be expressed in a homozygous condition

Q. Which of the following best describes the term 'genotype'?

A. The physical appearance of an organism
B. The genetic constitution of an organism
C. The environmental factors affecting a plant
D. The evolutionary history of a species

Solution

Genotype refers to the genetic constitution of an organism, which determines its potential traits.

Correct Answer: B — The genetic constitution of an organism

Q. Which of the following is a characteristic of a dominant allele?

A. It is always expressed in the phenotype
B. It can be masked by a recessive allele
C. It is only expressed in homozygous conditions
D. It is less common in a population

Solution

A dominant allele is expressed in the phenotype even when only one copy is present, masking the effect of a recessive allele.

Correct Answer: A — It is always expressed in the phenotype

Q. Which of the following is an example of a phenotype?

A. The genetic makeup of a plant
B. The color of a flower
C. The location of a plant in an ecosystem
D. The number of chromosomes in a cell

Solution

Phenotype refers to the observable characteristics of an organism, such as flower color, which result from the interaction of its genotype with the environment.

Correct Answer: B — The color of a flower

Q. Which of the following is NOT a mechanism of genetic variation in plants?

A. Mutation
B. Crossing over
C. Independent assortment
D. Asexual reproduction

Solution

Asexual reproduction does not introduce genetic variation, as it produces genetically identical offspring, unlike mutation, crossing over, and independent assortment.

Correct Answer: D — Asexual reproduction

Q. Which of the following processes increases genetic variation in plant populations?

A. Asexual reproduction
B. Cloning
C. Cross-pollination
D. Vegetative propagation

Solution

Cross-pollination introduces genetic variation by combining genetic material from different parent plants.

Correct Answer: C — Cross-pollination

Q. Which of the following terms describes the genetic makeup of an organism?

A. Phenotype
B. Genotype
C. Allele
D. Haploid

Solution

The genotype refers to the genetic makeup of an organism, while phenotype refers to the observable traits.

Correct Answer: B — Genotype

Q. Which type of inheritance involves multiple genes affecting a single trait?

A. Monogenic inheritance
B. Polygenic inheritance
C. Codominance
D. Incomplete dominance

Solution

Polygenic inheritance involves multiple genes contributing to a single trait, resulting in a range of phenotypes.

Correct Answer: B — Polygenic inheritance

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