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Molecular Basis of Inheritance MCQs

Class 12 Biology — questions with answers and worked explanations.

20 free questions Class 12 Biology Answers + explanations No sign-up

These questions are drawn from the Pariksha Sutra question bank for Molecular Basis of Inheritance, part of the Class 12 Biology syllabus. Each one shows the correct answer and, where a method helps, the working behind it.

Read the question, decide your answer before looking, then check the explanation — that is what turns practice into marks. If a question catches you out, the explanation is the part worth re-reading.

Questions

Question 1
Which scientists proposed the double helix model of DNA structure in 1953?
  1. Hershey and Chase
  2. Meselson and Stahl
  3. Watson and Crick
  4. Griffith and Avery
Answer: Watson and Crick
Question 2
A nucleotide consists of a nitrogenous base, a sugar and:
  1. A hydroxyl group only
  2. A fatty acid
  3. A phosphate group
  4. An amino acid
Answer: A phosphate group
Question 3
The transcriptionally active, loosely packed region of chromatin is called:
  1. Centromere
  2. Nucleolus
  3. Heterochromatin
  4. Euchromatin
Answer: Euchromatin
Question 4
Which enzyme treatment did NOT stop transformation in the Avery, MacLeod and McCarty experiment?
  1. Heat treatment
  2. Protease and RNase
  3. DNase
  4. Both DNase and RNase
Answer: Protease and RNase
Question 5
The enzyme that joins Okazaki fragments on the lagging strand is:
  1. DNA helicase
  2. DNA polymerase III
  3. DNA ligase
  4. Primase
Answer: DNA ligase
Question 6
A histone octamer is made up of:
  1. Four histone molecules
  2. Two histone molecules
  3. Eight histone molecules
  4. Six histone molecules
Answer: Eight histone molecules
Question 7
After bacteriophage infection, Hershey and Chase found that the radioactivity entering the bacterial cell was mainly:
  1. 35S from protein
  2. Both isotopes equally
  3. Neither isotope
  4. 32P from DNA
Answer: 32P from DNA
Question 8
The short DNA fragments formed on the lagging strand are called:
  1. Okazaki fragments
  2. Replicons
  3. Primers
  4. Introns
Answer: Okazaki fragments
Question 9
In bacterial transcription, the sigma (σ) factor is associated with which step?
  1. Termination
  2. Initiation
  3. Elongation
  4. Splicing
Answer: Initiation
Question 10
In a DNA double helix, the two strands are held together mainly by:
  1. Glycosidic bonds
  2. Hydrogen bonds between complementary bases
  3. Peptide bonds
  4. Phosphodiester bonds
Answer: Hydrogen bonds between complementary bases
Question 11
Adenine and guanine are examples of:
  1. Pyrimidines
  2. Pentose sugars
  3. Phosphate esters
  4. Purines
Answer: Purines
Question 12
In higher classes of organisms, packaging of chromatin at higher level requires an additional set of proteins collectively called:
  1. Ribosomal proteins
  2. Ligases
  3. Non-histone chromosomal (NHC) proteins
  4. RNA polymerase
Answer: Non-histone chromosomal (NHC) proteins
Question 13
In some viruses, such as tobacco mosaic virus, the genetic material is:
  1. RNA
  2. Protein
  3. DNA
  4. Lipid
Answer: RNA
Question 14
The Y-shaped structure formed at the site of DNA replication is called the:
  1. Operon
  2. Origin only
  3. Nucleosome
  4. Replication fork
Answer: Replication fork
Question 15
How many hydrogen bonds are present between adenine and thymine in DNA?
  1. Four
  2. One
  3. Three
  4. Two
Answer: Two
Question 16
The backbone of a DNA strand is formed by:
  1. Sugar and phosphate linked by phosphodiester bonds
  2. Nitrogen bases only
  3. Amino acids
  4. Hydrogen bonds
Answer: Sugar and phosphate linked by phosphodiester bonds
Question 17
The length of DNA in a typical human diploid cell is approximately:
  1. 2.2 millimetres
  2. 22 metres
  3. 2.2 metres
  4. 0.22 metres
Answer: 2.2 metres
Question 18
Which property makes DNA a better genetic material than RNA?
  1. It is more stable
  2. It is catalytically active
  3. It mutates faster
  4. It is single-stranded
Answer: It is more stable
Question 19
During replication, DNA polymerase requires energy for polymerisation which is supplied by:
  1. GTP only
  2. Deoxyribonucleoside triphosphates
  3. ATP only
  4. Inorganic phosphate
Answer: Deoxyribonucleoside triphosphates
Question 20
Guanine pairs with cytosine through how many hydrogen bonds?
  1. Three
  2. One
  3. Two
  4. Four
Answer: Three

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