MOLECULAR BASIS OF INHERITANCE CLASS XII

 

GANGWAR SIR BAREILLY

BIOLOGY

Class: 12 (2025-26)

CLASS TEST

TIME: 1.5 HOURS	M.M.: 50

General Instructions:

• This question paper contains 26 questions.

• All questions are compulsory.

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

• Q.6 to 8 (Assertion Reason Questions): 3 questions. Each question carries 1 mark.

• Q.9 to 13 (Very Short Answer Questions): 5 questions. Each question carries 1 mark.

• Q.14 to 18 (Short Answer Questions): 5 questions. Each question carries 2 marks.

• Q.19 to 24 (Long Answer Questions): 6 questions. Each question carries 3 marks.

• Q.25 to 25 (Competency Based Questions): 1 questions. Each question carries 4 marks.

• Q.26 to 26 (Comprehension Based Questions): 1 questions. Each question carries 5 marks.

Topics Covered:

• Molecular Basis of Inheritance

 

Q.NO.	QUESTIONS	MARKS
MULTIPLE CHOICE QUESTIONS (MCQS) Questions 1 to 5 (5 questions × 1 mark each)
1	Which enzyme is responsible for joining Okazaki fragments during DNA replication? A. DNA polymerase B. DNA ligase C. Helicase D. RNA primase	1
2	The process by which RNA is synthesized from a DNA template is called: A. Translation B. Transcription C. Replication D. Transformation	1
3	Which of the following nitrogenous bases is NOT found in RNA? A. Adenine B. Thymine C. Cytosine D. Uracil	1
4	In the lac operon model, what binds to the operator region to prevent transcription when lactose is absent? A. RNA polymerase B. Lactose C. Repressor protein D. CAP-cAMP complex	1
5	The human genome project was completed in which year? A. 1995 B. 2000 C. 2003 D. 2010	1
ASSERTION REASON QUESTIONS Questions 6 to 8 (3 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): DNA replication is semi-conservative.  Reason (R): Each new DNA molecule consists of one parental strand and one newly synthesized strand.	1
7	Assertion (A): DNA polymerase can synthesize DNA in both 5' to 3' and 3' to 5' directions.  Reason (R): DNA polymerase requires a primer to initiate synthesis.	1
8	Assertion (A): The genetic code is universal.  Reason (R): The same codons code for the same amino acids in all organisms.	1
VERY SHORT ANSWER QUESTIONS Questions 9 to 13 (5 questions × 1 mark each)
9	What is the length of DNA in a typical mammalian cell in base pairs?	1
10	Name the enzyme responsible for synthesizing RNA from a DNA template.	1
11	Name the enzyme responsible for joining Okazaki fragments during DNA replication.	1
12	What is the significance of the promoter region in DNA?	1
13	Name the enzyme responsible for synthesizing RNA primers during DNA replication.	1
SHORT ANSWER QUESTIONS Questions 14 to 18 (5 questions × 2 marks each)
14	Name the enzyme that helps in DNA replication by joining Okazaki fragments.	2
15	What is the function of RNA polymerase in transcription?	2
16	Explain the term 'codon' in the context of protein synthesis.	2
17	Differentiate between introns and exons in eukaryotic genes.	2
18	Describe the significance of the promoter region in transcription.	2
LONG ANSWER QUESTIONS Questions 19 to 24 (6 questions × 3 marks each)
19	Explain the process of DNA replication in prokaryotes, highlighting the role of enzymes involved.	3
20	Differentiate between transcription and translation in terms of their processes and products.	3
21	Describe the structure of a nucleosome and explain its significance in DNA packaging.	3
22	Explain the central dogma of molecular biology and discuss how it relates to gene expression.	3
23	Discuss the significance of the Human Genome Project in understanding genetic diseases.	3
24	Explain the concept of genetic code and its characteristics.	3
COMPETENCY BASED QUESTIONS Questions 25 to 25 (1 questions × 4 marks each)
25	In a research lab, scientists were studying the process of DNA replication in E. coli. They observed that replication starts at a specific site called the origin of replication (oriC) and proceeds bidirectionally. During their experiments, they introduced a mutation in the gene encoding DNA helicase, an enzyme crucial for unwinding the DNA helix. They also added a chemical that inhibits the activity of DNA ligase. Answer the following sub-questions based on this scenario: (i) What would be the immediate effect on DNA replication if DNA helicase is non-functional? (ii) How would the inhibition of DNA ligase affect the newly synthesized DNA strands? (iii) Explain the role of single-strand binding proteins (SSBs) in DNA replication. (iv) Predict the consequences if the origin of replication (oriC) is deleted from the bacterial chromosome. (v) Evaluate the importance of bidirectional replication in ensuring efficient DNA synthesis. A. (i) Describe the immediate effect on DNA replication if DNA helicase is non-functional B. (ii) Explain how the inhibition of DNA ligase would affect the newly synthesized DNA strands C. (iii) Analyze the role of single-strand binding proteins (SSBs) in DNA replication D. (iv) Predict the consequences if the origin of replication (oriC) is deleted from the bacterial chromosome E. (v) Evaluate the importance of bidirectional replication in ensuring efficient DNA synthesis	4
COMPREHENSION BASED QUESTIONS Questions 26 to 26 (1 questions × 5 marks each)
26	DNA Replication and Repair DNA replication is a fundamental process in all living organisms, ensuring the accurate transmission of genetic information from one generation to the next. The process begins at specific sites called origins of replication, where the DNA double helix unwinds and separates into two single strands. Enzymes like helicase and topoisomerase facilitate this unwinding. DNA polymerase then synthesizes new complementary strands by adding nucleotides in the 5' to 3' direction. The leading strand is synthesized continuously, while the lagging strand is synthesized in short segments called Okazaki fragments. Errors during replication can lead to mutations, but DNA repair mechanisms like proofreading by DNA polymerase and mismatch repair help correct these errors. Understanding DNA replication is crucial for insights into genetic disorders, cancer, and biotechnology applications. (1) What is the role of helicase in DNA replication? (2) Explain why the lagging strand is synthesized discontinuously. (3) How does DNA polymerase contribute to the accuracy of DNA replication? (4) Discuss the significance of origins of replication in DNA synthesis. (5) What are the implications of DNA repair mechanisms in preventing genetic disorders?	5