NEET (UG)

Practice Test 1 — Molecular Basis of Inheritance

12 questions • 18 minutes • auto-graded with full solutions

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Section A — MCQ (Single Correct)

Question 1

Guanine pairs with cytosine by:

Solution: G≡C is held by three hydrogen bonds.

Question 2

The pitch (one full turn) of the DNA helix is:

Solution: Pitch = 3.4 nm with 10 bp per turn.

Question 3

The transforming principle of Griffith was shown to be DNA by:

Solution: Avery, MacLeod and McCarty identified DNA as the transforming principle.

Question 4

DNA replication is best described as:

Solution: Each daughter DNA has one old and one new strand.

Question 5

The stop codons are:

Solution: UAA, UAG and UGA are stop codons.

Question 6

Splicing removes:

Solution: Introns are removed; exons are joined.

Question 7

In the lac operon, the repressor is coded by the:

Solution: The regulatory i gene codes for the repressor.

Question 8

The Human Genome Project was completed in:

Solution: HGP ran 1990–2003.

Section B — Assertion & Reason

Question 9

A: The G≡C base pair is stronger than the A=T base pair.
R: G pairs with C through three hydrogen bonds while A pairs with T through two.

Solution: More hydrogen bonds make G≡C stronger — R explains A.

Question 10

A: The lagging strand is synthesised discontinuously as Okazaki fragments.
R: DNA polymerase can add nucleotides only in the 5'→3' direction.

Solution: The 5'→3' restriction forces discontinuous lagging-strand synthesis — R explains A.

Question 11

A: In the lac operon, the genes are switched on when lactose is absent.
R: Lactose acts as an inducer that inactivates the repressor.

Solution: A is false — the genes are switched on when lactose is PRESENT; R is true (lactose is the inducer).

Question 12

A: DNA is generally preferred over RNA as the genetic material.
R: Being double-stranded, DNA is chemically more stable than single-stranded RNA.

Solution: Greater stability of double-stranded DNA is why it is preferred — R explains A.