Chapter 5: Molecular Basis of Inheritance Assertion-Reason Questions | biology Class 12 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): In a DNA double helix, if one strand has the sequence 5'-ATGC-3', the complementary strand is 3'-TACG-5'. Reason (R): The two strands of DNA are complementary and antiparallel, with A pairing with T and G pairing with C.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 2

Logic Check

Assertion (A): Uracil is present in DNA in place of thymine. Reason (R): DNA contains deoxyribose sugar whereas RNA contains ribose sugar.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 3

Logic Check

Assertion (A): Heterochromatin is transcriptionally inactive. Reason (R): Heterochromatin is densely packed and stains darkly, preventing access of RNA polymerase to the DNA.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 4

Logic Check

Assertion (A): In Griffith's experiment, the R strain bacteria injected alone into mice caused pneumonia. Reason (R): The R strain (rough) bacteria lack the polysaccharide coat and are non-virulent.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 5

Logic Check

Assertion (A): DNA is a better genetic material than RNA for long-term storage of information. Reason (R): DNA has thymine instead of uracil, lacks the reactive 2'-OH group, and is double-stranded allowing repair mechanisms.

Reasoning Options

ByteNotes

Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 6

Logic Check

Assertion (A): Meselson and Stahl's experiment proved that DNA replication is conservative. Reason (R): After one generation in 14N medium, they observed a single hybrid density DNA band in CsCl gradient.

Reasoning Options

ByteNotes

Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 7

Logic Check

Assertion (A): DNA polymerase can initiate replication independently without any primer. Reason (R): DNA replication is initiated at the origin of replication (ori) in E. coli.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 8

Logic Check

Assertion (A): In bacteria, transcription and translation can occur simultaneously. Reason (R): In bacteria, there is no nuclear membrane separating the cytoplasm from the genetic material, so translation can begin even before transcription is completed.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 9

Logic Check

Assertion (A): In eukaryotes, the primary transcript (hnRNA) can be directly used for translation. Reason (R): In eukaryotes, the primary transcript contains both introns and exons and must be processed before translation.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 10

Logic Check

Assertion (A): The genetic code is universal. Reason (R): The same codon codes for the same amino acid in almost all organisms, with minor exceptions in mitochondrial codons and some protozoans.

Reasoning Options

ByteNotes

Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 11

Logic Check

Assertion (A): Deletion of one base pair in a gene always results in a non-functional protein. Reason (R): Deletion of one base pair causes a frameshift mutation that alters the reading frame from the point of deletion.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 12

Logic Check

Assertion (A): tRNA is called an adapter molecule. Reason (R): tRNA has an anticodon loop that reads the mRNA codon and an amino acid acceptor end that carries the specific amino acid.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 13

Logic Check

Assertion (A): The ribosome acts as a catalyst for peptide bond formation. Reason (R): The 23S rRNA in the large subunit of the ribosome functions as a ribozyme catalysing peptide bond formation.

Reasoning Options

ByteNotes

Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 14

Logic Check

Assertion (A): In the lac operon, glucose can act as an inducer like lactose. Reason (R): The lac operon is regulated by the availability of an energy source for E. coli metabolism.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 15

Logic Check

Assertion (A): The lac operon is switched off in the absence of lactose in the growth medium. Reason (R): In the absence of lactose, the repressor produced by the i gene binds to the operator and prevents transcription of structural genes.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 16

Logic Check

Assertion (A): RNA is considered to have evolved before DNA. Reason (R): RNA can act both as a genetic material and as a catalyst (ribozyme), suggesting life evolved around RNA.

Reasoning Options

ByteNotes

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 17

Logic Check

Assertion (A): Euchromatin is found in metabolically less active cells. Reason (R): Euchromatin is loosely packed and allows the transcription machinery to access the DNA, making it transcriptionally active.

Reasoning Options

ByteNotes

Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 18

Logic Check

Assertion (A): Insertions or deletions of three base pairs do not cause frameshift mutations. Reason (R): Insertion or deletion of three (or multiples of three) bases inserts or deletes one or more codons, leaving the reading frame intact from that point.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 19

Logic Check

Assertion (A): The Human Genome Project was completed in 1990. Reason (R): The Human Genome Project was a 13-year project coordinated by the U.S. Department of Energy and the National Institutes of Health.

Reasoning Options

ByteNotes

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 20

Logic Check

Assertion (A): DNA fingerprinting cannot distinguish between monozygotic twins. Reason (R): Monozygotic twins originate from the same fertilised egg and have identical DNA sequences.

Reasoning Options

ByteNotes

Chapter sections

Chapter 5: Molecular Basis of Inheritance | Assertion-Reason

Assertion (A): In a DNA double helix, if one strand has the sequence 5'-ATGC-3', the complementary strand is 3'-TACG-5'. Reason (R): The two strands of DNA are complementary and antiparallel, with A pairing with T and G pairing with C.

Assertion (A): Uracil is present in DNA in place of thymine. Reason (R): DNA contains deoxyribose sugar whereas RNA contains ribose sugar.

Assertion (A): Heterochromatin is transcriptionally inactive. Reason (R): Heterochromatin is densely packed and stains darkly, preventing access of RNA polymerase to the DNA.

Assertion (A): In Griffith's experiment, the R strain bacteria injected alone into mice caused pneumonia. Reason (R): The R strain (rough) bacteria lack the polysaccharide coat and are non-virulent.

Assertion (A): DNA is a better genetic material than RNA for long-term storage of information. Reason (R): DNA has thymine instead of uracil, lacks the reactive 2'-OH group, and is double-stranded allowing repair mechanisms.

Assertion (A): Meselson and Stahl's experiment proved that DNA replication is conservative. Reason (R): After one generation in 14N medium, they observed a single hybrid density DNA band in CsCl gradient.

Assertion (A): DNA polymerase can initiate replication independently without any primer. Reason (R): DNA replication is initiated at the origin of replication (ori) in E. coli.

Assertion (A): In bacteria, transcription and translation can occur simultaneously. Reason (R): In bacteria, there is no nuclear membrane separating the cytoplasm from the genetic material, so translation can begin even before transcription is completed.

Assertion (A): In eukaryotes, the primary transcript (hnRNA) can be directly used for translation. Reason (R): In eukaryotes, the primary transcript contains both introns and exons and must be processed before translation.

Assertion (A): The genetic code is universal. Reason (R): The same codon codes for the same amino acid in almost all organisms, with minor exceptions in mitochondrial codons and some protozoans.

Assertion (A): Deletion of one base pair in a gene always results in a non-functional protein. Reason (R): Deletion of one base pair causes a frameshift mutation that alters the reading frame from the point of deletion.

Assertion (A): tRNA is called an adapter molecule. Reason (R): tRNA has an anticodon loop that reads the mRNA codon and an amino acid acceptor end that carries the specific amino acid.

Assertion (A): The ribosome acts as a catalyst for peptide bond formation. Reason (R): The 23S rRNA in the large subunit of the ribosome functions as a ribozyme catalysing peptide bond formation.

Assertion (A): In the lac operon, glucose can act as an inducer like lactose. Reason (R): The lac operon is regulated by the availability of an energy source for E. coli metabolism.

Assertion (A): The lac operon is switched off in the absence of lactose in the growth medium. Reason (R): In the absence of lactose, the repressor produced by the i gene binds to the operator and prevents transcription of structural genes.

Assertion (A): RNA is considered to have evolved before DNA. Reason (R): RNA can act both as a genetic material and as a catalyst (ribozyme), suggesting life evolved around RNA.

Assertion (A): Euchromatin is found in metabolically less active cells. Reason (R): Euchromatin is loosely packed and allows the transcription machinery to access the DNA, making it transcriptionally active.

Assertion (A): Insertions or deletions of three base pairs do not cause frameshift mutations. Reason (R): Insertion or deletion of three (or multiples of three) bases inserts or deletes one or more codons, leaving the reading frame intact from that point.

Assertion (A): The Human Genome Project was completed in 1990. Reason (R): The Human Genome Project was a 13-year project coordinated by the U.S. Department of Energy and the National Institutes of Health.

Assertion (A): DNA fingerprinting cannot distinguish between monozygotic twins. Reason (R): Monozygotic twins originate from the same fertilised egg and have identical DNA sequences.

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