PRINCIPLES OF INHERTANCE AND VARIATION

 

Class: 12 (2025-26)

CLASS TEST

TIME: 2 HOURS	M.M.: 50

General Instructions:

• This question paper contains 22 questions.

• All questions are compulsory.

• Q.1 to 5 (Multiple Choice Questions (MCQs)): 5 questions. Each question carries 1 mark.

• Q.6 to 7 (Assertion Reason Questions): 2 questions. Each question carries 1 mark.

• Q.8 to 11 (Very Short Answer Questions): 4 questions. Each question carries 1 mark.

• Q.12 to 16 (Short Answer Questions): 5 questions. Each question carries 2 marks.

• Q.17 to 21 (Long Answer Questions): 5 questions. Each question carries 5 marks.

• Q.22 to 22 (Competency Based Questions): 1 questions. Each question carries 4 marks.

Topics Covered:

• Principles of Inheritance and Variation

 

Q.NO.	QUESTIONS	MARKS
MULTIPLE CHOICE QUESTIONS (MCQS) Questions 1 to 5 (5 questions × 1 mark each)
1	In Mendelian inheritance, which law states that alleles of different genes assort independently of one another during gamete formation? A. Law of Segregation B. Law of Dominance C. Law of Independent Assortment D. Law of Recombination	1
2	A plant with genotype TtYy is crossed with a plant with genotype Ttyy. What is the probability of obtaining an offspring with genotype TtYy? A. 1/4 B. 1/2 C. 1/8 D. 1/16	1
3	Which of the following genetic disorders is caused by a mutation in a single gene? A. Down Syndrome B. Turner Syndrome C. Sickle Cell Anemia D. Klinefelter Syndrome	1
4	In a dihybrid cross involving two heterozygous parents (AaBb x AaBb), what is the expected phenotypic ratio in the F1 generation? A. 9:3:3:1 B. 1:1:1:1 C. 3:1 D. 1:2:1	1
5	A woman with blood group AB marries a man with blood group O. What is the probability that their child will have blood group A? A. 0% B. 25% C. 50% D. 75%	1
ASSERTION REASON QUESTIONS Questions 6 to 7 (2 questions × 1 mark each) Instructions: The following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions by selecting the appropriate option given below: A. Both A and R are true, and R is the correct explanation of A. B. Both A and R are true, and R is not the correct explanation of A. C. A is true but R is false. D. A is false but R is true.
6	Assertion (A): In Mendelian inheritance, the F2 generation shows a phenotypic ratio of 3:1 in a monohybrid cross.  Reason (R): The F1 generation produces gametes with two different alleles in equal proportions.	1
7	Assertion (A): Codominance results in offspring with a phenotype that is distinct from both parents.  Reason (R): In codominance, both alleles in a heterozygote are fully expressed.	1
VERY SHORT ANSWER QUESTIONS Questions 8 to 11 (4 questions × 1 mark each)
8	Define incomplete dominance with an example.	1
9	What is the phenotypic ratio observed in the F2 generation of a monohybrid cross? A. 3:1 B. 1:2:1 C. 9:3:3:1 D. 1:1	1
10	Explain why Mendelian inheritance patterns may not always be observed in all organisms.	1
11	Assertion (A): The law of independent assortment is always applicable.  Reason (R): Genes located on the same chromosome assort independently.	1
SHORT ANSWER QUESTIONS Questions 12 to 16 (5 questions × 2 marks each)
12	Explain Mendel's law of segregation using the concept of alleles.	2
13	How does incomplete dominance differ from codominance? Provide an example of each.	2
14	Describe the significance of test crosses in genetic studies.	2
15	Compare the mechanisms of sex determination in cockroaches and Drosophila, highlighting one key difference in their chromosomal systems.	2
16	Explain how polygenic inheritance contributes to continuous variation in traits.	2
LONG ANSWER QUESTIONS Questions 17 to 21 (5 questions × 5 marks each)
17	Explain the significance of Mendel's dihybrid cross experiment in establishing the Law of Independent Assortment. Discuss how this principle is violated during gene linkage.	5
18	A plant with genotype AaBb (where A=Tall, a=dwarf; B=Red flowers, b=white) was test crossed. The progeny showed 42% parental types and 8% recombinants each for Ab & aB. (a) Calculate the map distance between these genes (b) Explain why the recombination frequency isn't 50%	5
19	Compare and contrast incomplete dominance and codominance using specific examples. How do these phenomena challenge Mendel's principle of dominance?	5
20	Explain the phenomenon of pleiotropy with a suitable example. Discuss how pleiotropy influences the inheritance patterns of genetic disorders and provide insights into its implications for genetic counseling.	5
21	Describe the chromosomal theory of inheritance with experimental evidence. How did Morgan's work with Drosophila provide crucial support for this theory?	5
COMPETENCY BASED QUESTIONS Questions 22 to 22 (1 questions × 4 marks each)
22	Down syndrome, Klinefelter syndrome, and Turner syndrome are genetic disorders resulting from chromosomal abnormalities. Down syndrome is characterized by trisomy of chromosome 21, Klinefelter syndrome by the presence of an extra X chromosome in males (47,XXY), and Turner syndrome by the absence of one X chromosome in females (45,X). Analyze the genetic constitution and phenotypic characteristics of individuals with these syndromes. A. Explain how non-disjunction during meiosis leads to the chromosomal abnormalities observed in Down syndrome, Klinefelter syndrome, and Turner syndrome. B. Compare and contrast the phenotypic characteristics of individuals with Down syndrome, Klinefelter syndrome, and Turner syndrome. C. Evaluate the impact of these syndromes on fertility and reproductive health. D. Discuss the genetic counseling considerations for families with a history of these syndromes. E. Propose a strategy for early diagnosis and management of these genetic disorders.	4