Match List-I with List-II.

[Molecular-Basis-of-Inheritance] [class-xii ]

• A-II, B-I, C-IV, D-III
• A-I, B-II, C-IV, D-III
• A-II, B-IV, C-I, D-III
• A-III, B-I, C-II, D-IV
Correct Option: A  [ A-II, B-I, C-IV, D-III ]

Remark: VNTR stands for Variable Number of Tandem Repeats, a class of satellite DNA used as a marker. Polymorphism is a variation in DNA sequence observed in a population at a frequency greater than 0.01 (1%). A Probe is a radioactive single-stranded DNA used to detect specific sequences. PCR (Polymerase Chain Reaction) is used to amplify small DNA samples to increase sensitivity.

Match List-I with List-II.

[Molecular-Basis-of-Inheritance] [class-xii ]

• A-III, B-I, C-II, D-IV
• A-I, B-III, C-II, D-IV
• A-III, B-II, C-I, D-IV
• A-II, B-IV, C-I, D-III
Correct Option: A  [ A-III, B-I, C-II, D-IV ]

Remark: Heterochromatin is the densely packed, dark-staining region of chromatin that is transcriptionally inactive. Euchromatin is the loosely packed, light-staining region that is transcriptionally active. The Nucleosome consists of DNA wrapped around a histone octamer, giving the appearance of "beads-on-string". Histones are the positively charged basic proteins that form the core of the nucleosome.

Which isotope was used by Meselson and Stahl to distinguish between heavy and light DNA?

[Molecular-Basis-of-Inheritance] [class-xii ]

• N-14 and N-15
• P-32 and P-35
• S-35 and P-32
• C-12 and C-14
Correct Option: A  [ N-14 and N-15 ]

Remark: Meselson and Stahl used the heavy isotope of nitrogen (N-15) and the normal light isotope (N-14) to prove the semi-conservative nature of DNA replication. N-15 is not a radioisotope but a heavy isotope distinguishable by centrifugation.

Taylor and colleagues used which radioactive molecule to prove semi-conservative replication in Vicia faba?

[Molecular-Basis-of-Inheritance] [class-xii ]

• Radioactive Adenine
• Radioactive Uracil
• Radioactive Thymidine
• Radioactive Guanine
Correct Option: C  [ Radioactive Thymidine ]

Remark: Taylor and his colleagues used radioactive thymidine to detect the distribution of newly synthesized DNA in the chromosomes of Vicia faba (faba beans), proving semi-conservative replication in eukaryotes.

The enzyme responsible for relieving torsional strain (supercoiling) ahead of the replication fork is?

[Molecular-Basis-of-Inheritance] [class-xii ]

• Helicase
• DNA Ligase
• Topoisomerase (DNA Gyrase)
• Primase
Correct Option: C  [ Topoisomerase (DNA Gyrase) ]

Remark: As Helicase unwinds the DNA, tension or supercoiling builds up ahead of the fork. Topoisomerase (specifically DNA Gyrase in prokaryotes) relieves this tension by cutting and resealing the DNA.

In DNA replication, the primer used to initiate synthesis is chemically?

[Molecular-Basis-of-Inheritance] [class-xii ]

• DNA
• RNA
• Protein
• Lipid
Correct Option: B  [ RNA ]

Remark: DNA polymerase cannot initiate synthesis on its own; it requires a free 3-prime OH group. This is provided by a short stretch of RNA called an RNA primer, synthesized by the enzyme Primase.

Which enzyme removes the RNA primers after DNA replication in bacteria?

[Molecular-Basis-of-Inheritance] [class-xii ]

• DNA Polymerase III
• DNA Polymerase I
• Primase
• Ligase
Correct Option: B  [ DNA Polymerase I ]

Remark: DNA Polymerase I is responsible for removing the RNA primers and filling the gaps with DNA nucleotides. DNA Polymerase III is the main replicating enzyme.

The discontinuously synthesized DNA fragments on the lagging strand are known as?

[Molecular-Basis-of-Inheritance] [class-xii ]

• Leading fragments
• Okazaki fragments
• Sigma fragments
• Klenow fragments
Correct Option: B  [ Okazaki fragments ]

Remark: The lagging strand is synthesized in short segments called Okazaki fragments because DNA polymerase can only synthesize in the 5-prime to 3-prime direction, moving away from the replication fork on this strand.

Which enzyme acts as the "molecular glue" to join DNA fragments?

[Molecular-Basis-of-Inheritance] [class-xii ]

• DNA Polymerase
• DNA Helicase
• DNA Ligase
• Topoisomerase
Correct Option: C  [ DNA Ligase ]

Remark: DNA Ligase joins the discontinuous Okazaki fragments on the lagging strand by forming phosphodiester bonds, acting as a molecular glue.

The energy required for adding nucleotides during DNA replication is provided by?

[Molecular-Basis-of-Inheritance] [class-xii ]

• ATP only
• Deoxyribonucleoside triphosphates (dNTPs)
• Ribonucleoside triphosphates
• Enzymes
Correct Option: B  [ Deoxyribonucleoside triphosphates (dNTPs) ]

Remark: The substrates for replication are dNTPs (like dATP, dGTP, etc.). They serve a dual purpose: acting as substrates and providing energy through the breakdown of their two terminal phosphates.