The fact that a purine always paired base through hydrogen bonds with a pyrimidine base leads to _______ in the DNA double helix.

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

• Antiparallel nature
• Uniform width
• Semi-conservative nature
• Right handed coiling
Correct Option: B  [ Uniform width ]

Remark: Purine-Pyrimidine pairing ensures uniform diameter.

The net electric charge on DNA and histones is _______

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

• Both positive
• Both negative
• Negative and positive
• Zero
Correct Option: C  [ Negative and positive ]

Remark: DNA is negative, Histones are positive.

The first genetic material could be _______

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

• Protein
• Carbohydrates
• DNA
• RNA
Correct Option: D  [ RNA ]

Remark: RNA came first.

The human chromosome with the highest and least number of genes are _______ and _______ respectively.

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

• Chromosome 21 and Y
• Chromosome 1 and X
• Chromosome 1 and Y
• Chromosome X and Y
Correct Option: C  [ Chromosome 1 and Y ]

Remark: Chr 1 has max, Y has min genes.

Who amongst the following scientists had no contribution in the development of the double helix model for the structure of DNA?

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

• Rosalind Franklin
• Maurice Wilkins
• Erwin Chargaff
• Meselson and Stahl
Correct Option: D  [ Meselson and Stahl ]

Remark: Meselson and Stahl worked on replication, not the structure model itself.

DNA is a polymer of nucleotides which are linked to each other by 3' to 5' phosphodiester bond. To prevent polymerization of nucleotides, which of the following modifications would you choose?

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

• Replace purine with pyrimidine
• Remove/Replace 3' OH group in deoxyribose
• Remove/Replace 2' OH group with some other group in deoxyribose
• Both B and C
Correct Option: B  [ Remove/Replace 3' OH group in deoxyribose ]

Remark: Polymerization requires a free 3' OH.

Discontinuous synthesis of DNA occurs in one strand, because _______

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

• DNA molecule being synthesized is very long
• DNA dependent DNA polymerase catalyzes polymerization only in one direction (5' -> 3')
• It is a more efficient process
• DNA ligase has to have a role
Correct Option: B  [ DNA dependent DNA polymerase catalyzes polymerization only in one direction (5' -> 3') ]

Remark: The enzyme only works 5' to 3'.

Which of the following steps in transcription is catalyzed by RNA polymerase?

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

• Initiation
• Elongation
• Termination
• All of the above
Correct Option: D  [ All of the above ]

Remark: RNA Pol does all 3, with help from factors for init/term.

Control of gene expression in prokaryotes takes place at the level of _______

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

• DNA-replication
• Transcription
• Translation
• None of the above
Correct Option: B  [ Transcription ]

Remark: Transcription initiation is the main control point.

Regulatory proteins are the accessory proteins that interact with RNA polymerase and affect its role in transcription. Which of the following statements is correct about regulatory protein?

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

• They only increase expression
• They only decrease expression
• They interact with RNA polymerase but do not affect expression
• They can act both as activators and as repressors
Correct Option: D  [ They can act both as activators and as repressors ]

Remark: Regulatory proteins can activate or repress transcription.