CBSE Important Questions Class 12 Biology Chapter 5

Important Questions Class 12 Biology Chapter 5

Important Questions for CBSE Class 12 Biology Chapter 5 – Principles of Inheritance and Variation

Important Questions Class 12 Biology Chapter 5 provides students with well-explained answers to the chapter’s most important and frequently asked questions,  for each student to learn and understand the chapter more easily and to perform well in their exams. With Chapter 5 Class 12 Biology Important Questions, students can improve their board preparations significantly and aim for the highest score to create their first milestone.

CBSE Class 12 Biology Chapter 5 Important Questions

‌Study Important Question for Class 12 Biology Chapter 5 – Principles of Inheritance and Variation

Here are a few of the important questions for Class 12 Biology Chapter 5.

Very Short Answer Questions (1 Mark)

Q1. Give any two reasons for the selection of pea plants by Mendel for his experiments. 

Ans: The two reasons for the selection of pea plants by Mendel for his experiments are:

(i) Many varieties are present with contrasting forms of characters. 

(ii) They can be easily cross-pollinated as well as self-pollinated. 

Q2. Name any one plant that shows the phenomenon of incomplete dominance during the inheritance of its flower colour. 

Ans: The plant that shows the phenomenon of incomplete dominance during the inheritance of its flower colour is Dog flower or Snapdragon (Antirrhinum sp.)

Q3. Name the base change and the amino acid change, responsible for sickle cell anaemia. 

Ans: The change in base GAG as GUG and substitution of Glutamic acid by valine is responsible for sickle cell anaemia. 

Q4. A haemophilic man marries a normal homozygous woman. What is the probability that their daughter will be haemophilic? 

Ans: When a haemophilic man marries a normal homozygous woman, their daughter has a 0% chance of being haemophilic.

Q5. What is meant by aneuploidy? 

Ans: Aneuploidy is the phenomenon of the existence or loss of one or more chromosomes due to failure in the separation of members of a homologous pair of chromosomes during meiosis. 

Q6. What genetic principle could be derived from a monohybrid cross? 

Ans: The genetic principle derived from a monohybrid cross is The Law of dominance.

Q7. What is a test cross? 

Ans: A test cross is a cross in which offspring with a dominant phenotype is crossed with offspring with a homozygous recessive genotype to determine the offspring’s genotype for a specific trait.

Q8. What is mutagen? Give an example. 

Ans: The physical or chemical agents that cause mutations are called mutagens. For example  x-rays, CNBr etc. 

Short Answer Questions (2 Marks)

Q1. Identify the sex of the organism as male or female in which the sex chromosome is found in: 

(i) ZW in birds 

Ans: ZW in birds: Female 

(ii) XY in Drosophila

Ans: XY in Drosophila: Male

(iii) ZZ in birds  

Ans: ZZ in birds: Female 

(iv) XO in grasshoppers

Ans: XO in grasshopper: Male 

Q2. The human male never passes on the gene for haemophilia to his son. Why is it so? 

Ans. Since the haemophilia gene is present on the X chromosome, the human male never passes it on to his son. A male inherits only one X chromosome from his mother and one Y chromosome from his father. The human male passes on the X chromosome to his daughters or female progeny but not to his sons or male progeny.

Q3. Which law of Mendel is universally accepted? State the law.  

Ans: Mendel’s law of segregation is universally accepted. The law states that – “The two alleles of a gene remain separate and do not contaminate each other in F1 or the hybrid. At the time of gamete formation, two alleles get separated and pair into different gametes”. 

Long Answer Questions (3 Marks)

Q1. Explain the cause of Klinefelter​’s syndrome. Give any four symptoms of this syndrome. 

Ans: The presence of an extra chromosome in males i.e., XXY is the cause of Klinefelter​’s syndrome. The symptoms found in the sufferer of Klinefelter’s syndrome are the development of breasts, female-type pubic hair pattern, poor beard growth, underdeveloped testes, and tall stature with a feminised physique.

Q2. How is sex determined in humans?

Ans: All females have a pair of X-chromosomes, whereas males have one X-chromosome and one Y-chromosome, which is smaller in size. Thus, in a male-female cross, there is an equal chance of males and females in the progeny, and sex is determined by the presence of a Y-chromosome in the progeny. If a Y-chromosome is present, the child is male; otherwise, the child is female.

Class 12 Biology Principles of Inheritance and Variation Important Questions

Important Questions of Chapter 5 Biology Class 12

Extramarks provides Chapter 5 Class 12 Biology Important Questions with a very simplified explanation of all the major questions, to help students ace their Biology exams. This Class 12 Biology Chapter 5 Important Questions would be useful for board exam preparations. Students can also find answers to questions which they might have found difficult to answer   while learning. 

These sets of questions cover all of the main concepts, topics, and key points of the chapter as well as chapter-end exercises. Students can refer to Important Questions Class 12 Biology Chapter 5 from Extramarks to get a general idea of the answer-writing pattern in the board exams. They can use these solutions to quickly and efficiently answer Chapter 5 Class 12 Biology Important Questions.

It can also be helpful in the last-minute revision of important concepts before the exam. The Biology Class 12 Chapter 5 Important Questions is easily accessible from the Extramarks website. 

Class 12 Biology Chapter 5 Important Questions – Summary

Heredity is a mechanism that transfers heritable traits and genes from parents to their progeny.

Genetics is the branch of Biology that studies the concepts and mechanisms of inheritance and variation.

Inheritance is the basis of inheritance and characteristics are passed down from the parents to the offspring through this process. The inheritance mechanism ensures the continuity of the gene pool.

Genes are the basic unit of inheritance and are found on chromosomes.

Variation exists among individuals of the same species. Recombination, crossing over, environmental effects, and mutation on the expression of genes found on chromosomes can all cause variation.

Mendel’s Law of Inheritance:

The Law of Dominance states that:

  • Characters are regulated by discrete units that are called factors.
  • Factors often emerge in pairs.
  • One member of a pair dominates the other in a distinct pair of factors.

The Law of Segregation states:

During the process of meiosis, at the time of gamete formation, each allele is separated. There is no blending in this process, and the characters are found to be passed to distinct gametes. Homozygotes can be produced using only one type of gamete, whereas heterozygotes require the use of two different types of gametes.

The Law of Independent Assortment states that:

According to the law, “when two pairs of characteristics are mixed in a hybrid, the segregation of one pair of characters is independent from the segregation of the other pair of characters.” Due to an independent assortment of seed colour, i.e. yellow and green, and seed shape characteristics, i.e. round, wrinkled, two new combinations are produced in Dihybrid cross, round green & wrinkled yellow.

Chromosomal Theory of Inheritance:

Sutton and Boveri accepted Mendel’s findings and claimed that chromosomes are the carriers of genes.

Chromosomes exist as homologous pairs, and a gene’s two alleles are found on the same pair of chromosomes.

During meiosis, homologous chromosomes differentiate during gamete formation.

Chromosomes segregate and assort on their own.

When gametes mate, they produce progenies with a diploid number of chromosomes that are similar to the parents. Gamete fusion occurs during fertilisation.

Morgan conducted extensive research on fruit flies, Drosophila melanogaster, and provided experimental evidence to support the chromosomal theory of inheritance.

Linkage and Recombination:

Linkage refers to the physical association of chromosome-located genes.

If two genes in a dihybrid cross are closely related or located on the same chromosome, the parental combination is far more common than recombinants or non-parental combinations.

The amount of recombination and linkage depends on the distance between the two genes. The likelihood of recombination increases as the distance between the genes increases.

Sex Determination:

Different species have different sex determination mechanisms.

Henking first noticed the X chromosome and dubbed it the X body.

The chromosomes that determine sexual character formation are known as sex chromosomes, and the rest of the chromosomes are known as autosomes.

Male heterogamety occurs when a male develops two distinct types of gametes. Grasshoppers, humans, drosophila, and other organisms are examples.

Female heterogamety occurs when a female develops two distinct types of gametes. Examples may include birds.


A mutation is defined as any change in the DNA sequence. It has been observed that viable mutations are passed down from generation to generation.

This process of altering the DNA sequence may affect both the genotype and the phenotype of an organism.

It is linked to a variety of diseases, though not all mutations are harmful.

The mutation causes changes such as deletion, addition, replication, replacement, and so on. Mutation is a major cause of cancer.

Genetic Disorders:

Mendelian and chromosomal disorders are the two main types of genetic disorders.

  1. Mendelian Disorders:

Mendelian disorders are caused by a single gene mutation.

It follows the same inheritance pattern as Mendel’s rule.

Pedigree Analysis can be used to determine the inheritance pattern as well as whether the trait is dominant or recessive.

Mendelian disorders include sickle cell anaemia, muscular dystrophy, colour blindness, thalassemia, cystic fibrosis, and phenylketonuria.

Chromosomal Disorders:

Chromosomal diseases are illnesses caused by the absence, excess, or irregular arrangement of chromosomes.

Chromosome disorders are classified into two types:

Aneuploidy is the gain or loss of one or more chromosomes. It happens as a result of chromatid segregation failure during meiosis anaphase.

Polyploidy is a common trait in plants. This results in an increase in chromosome number.

Turner’s syndrome, Down syndrome, and other chromosomal disorders are examples.


Extramarks Important Questions Class 12 Biology Chapter 5 covers all of the important topics. Mendel’s Laws of Inheritance, Chromosomal Theory of Inheritance, Linkage and Recombination, Mutation, Sex Determination, and Genetic Disorders were all discussed. All of these concepts are crucial from both the board and competitive examination points of view.

FAQs (Frequently Asked Questions)

1. What is the study of inheritance and variation called?

Genetics is the study of inheritance and variation, as discussed in the chapter. In layman’s language, one aspect of genetics is the scientific study of variations passed down from parent to progeny. A common example can help you understand the concept of inheritance and variation. We frequently notice that children have several characteristics that are similar to their parents because they ‘inherited’ these characteristics from their parents. Similarly, because of a ‘variation’ in their genes, the children do not look exactly like their parents.

2. What are the important questions of Chapter 5 Principles of Inheritance and Variation of Class 12 Biology?

Students can access  the Important Questions Class 12 Biology Chapter 5 Principles of Inheritance and Variation from the Extramarks website. These questions cover all the main  topics of the chapter. Students can get a good score  if they thoroughly prepare these questions and practise NCERT textbook chapter end exercises. These questions were created by analysing past year’s questions as well as the updated recent syllabus. As a result, these questions will assist students in getting the highest possible score in the Biology board exam.