Biology: Molecular Basis of Inheritance (Solved Examples Part 1)

Want guaranteed success in NEET Molecular Biology? PracBee presents 25 essential solved examples covering the complete syllabus of Molecular Basis of Inheritance. From analyzing DNA replication mechanisms to understanding gene expression control, our detailed solutions make learning molecular genetics engaging and effective. Each example is enriched with experimental data interpretation, molecular technique applications, and real-world connections. Master concepts like DNA repair pathways, genetic code degeneracy, and operon regulation through our systematic approach. Designed by NEET experts, these solutions transform complex biological concepts into high-scoring answers.


1. Technique used to transfer ssDNA from gel to nitrocellulose membrane is called as

A . Northern blotting

B . Southern blotting

C . Western blotting

D . Gel electrophoresis

Solution:

Southern blotting is a laboratory technique used to defect a specific DNA sequence in a sample of tissue. Western blotting is used to detect protein, Northern blotting (RNA blot) is used to study gene expression by detection of RNA in a sample.

Correct Answer : B

2. The structural gene in a transcription unit could be said as polycistronic

A . In eukaryotes only

B . Mostly in bacteria

C . In prokaryotes only

D . Mostly in eukaryotes

Solution:

Polycistronic condition also found in some species of nematodes, drosophila, plant. etc. so more accurate answer will be mostly in bacteria.

Correct Answer : B

3. Information flow or central dogma of modern biology is

A . RNA -Proteins - DNA

B . DNA - RNA - RNA}

C . RNA - DNA -Proteins

D . DNA - RNA -Proteins

Solution:

Central dogma term was proposed by Crick (1958). It proposes unidirectional or one way flow of information from DNA to RNA and then to protein (polypeptide).

Correct Answer : D

4. If there are 999 bases in an RNA that code for a protein with 333 amino acids, and the base at position 901 is deleted such that the length of the RNA becomes 998 bases, how many codons will be altered?

A . 11

B . 33

C . 333

D . 1

Solution:

1 codon consists of 3 bases. Therefore, a deletion on 901 positions will affect 33 codons.

Correct Answer : B

5. How many bases are found in ds DNA (B-type) if the molecule turns by 360°  ?

A . 20

B . 10

C . 40

D . 36

Solution:

For 360° turn i.e., one helix there is 10 base pair in B-DNA.

Correct Answer : A

6. If in an m-RNA base sequence is 5 -AUG CUA UAC CUC CUU UAU CUG UGA-3'. How many amino acid residues will make up the polypeptide corresponding to this m-RNA?

A . Ten

B . Seven

C . Eight

D . Eleven

Solution:

Each amino acid consist of coding triplet nitrogenous bases known as codon. UGA is a terminating codon, which doesn't code for any amino acid.

Correct Answer : B

7. Eight molecules of____ different histone proteins

A . 5 , constitute 'beads on string structure'

B . 4 , constitute 'one nucleosome'

C . 4 , constitute 'two nucleosomes'

D . 5 , do not exist in eukaryotes

Solution:

Eight molecules of histone core constitutes one nucleosome.

Correct Answer : B

8. The unequivocal proof that DNA is the genetic material came from an experiment

A . By Meselson and Stahl

B . Where a bacteria was injected into bacteriophage

C . Where phage DNA was labelled with radioactive Sulphur

D . Which proved that DNA enter into bacteria whereas protein remain outside

Solution:

The unequivocal proof that DNA is the genetic material came from an experiment by Harshey & Martha Chase which proved that DNA enter into bacteria whereas protein remain outside.

Correct Answer : D

9. Nucleotide arrangement in DNA can be seen by

A . X-ray crystallography

B . electron microscope

C . ultracentrifuge

D . light microscope

Solution:
X-ray crystallography is the study of molecular structure by examining diffraction patterns made by x-rays beamed through a crystalline form of the molecules. It is widely used in biochemistry to examine the molecular structure of molecules such as proteins and DNA.

Correct Answer : A

10. What sequence on the template strand of DNA corresponds to the first amino acid inserted into a protein?

A . TAC

B . UAC

C . UAG

D . AUG

Solution:

The first mRNA codon to specify an amino acid is always AUG. A DNA strand with the sequence TAC will corresponds to the first amino acid i.e., AUG.

Correct Answer : A

11. Which of the following enzyme produces replication fork at the time of replication?

A . Primase

B . Helicase

C . Ligase

D . Topoisomerase

Solution:

Helicase is the enzyme which opens replication fork in DNA at the onset of replication.

Correct Answer : B

12. DNA fingerprinting involves identifying differences in some specific regions in DNA sequence, called as:

A . Satellite DNA

B . Repetitive DNA

C . Single nucleotides

D . Polymorphic DNA

Solution:

DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called repetitive DNA because in these sequences a small stretch of DNA is repeated many times. These sequences normally do not code for any proteins, but they form a large portion of the human genome. These sequences show a high degree of polymorphism and form the basis of DNA fingerprinting.

Correct Answer : B

13. What is the main function of tRNA in relation to protein synthesis?

A . Initiates transcription

B . Inhibits protein synthesis.

C . Identifies amino acids and transport them to ribosomes.

D . proofreading,

Solution:

tRNA (or transfer RNA) is a single stranded RNA molecule which brings amino acid at the site of protein synthesis and reads the genetic code in the process of transcription.

Correct Answer : C

14. Which of the following is not the features of DNA double helix?

A . The backbone is constituted by sugar- phosphate and the base project outside

B . A purine always pairs with pyrimidine

C . The pitch of helix is 3.4 nm and there are roughly 10 base pair in each turn

D . Plane of one base pair stacks over the other in double helix

Solution:

DNA bases are projected inside the double helix chain.

Correct Answer : A

15. In some viruses, RNA is present instead of DNA indicating that

A . their nucleic acid must combine with host DNA before replication.

B . they cannot replicate.

C . there is no hereditary information.

D . RNA can act to transfer heredity.

Solution:

RNA and DNA both are genetic material and carry genetic information from one generation to other. A virus is a small parasite that cannot reproduce by itself. Most viruses have either RNA or DNA as their genetic material. Once a virus infects a susceptible cell, it can direct the cell machinery to produce more viruses.

Correct Answer : D

16. In Lac operon, the regulatory gene is also called i gene, here the term

i is derived from the word

A . Inducer

B . Integrator

C . Inhibitor

D . Inactive repressor

Solution:

The regulatory gene in lac operon is i gene. Here i is derived from 'inhibitory' since its product inhibits transcription.

Correct Answer : C

17. Commonly used vectors in human genome project:-
A. YAC and MAC
B. YAC and BAC
C.  and MAC
D. Only YAC

Solution:

Yeast artificial chromosome (YAC) and Bacterial artificial chromosomes (BAC) are used as a vector in HGP. They can transfer large DNA segments.

Correct Answer : B

18. In some viruses the flow of information is in reverse direction,that is, from RNA to DNA. This process can be termed as

A . Teminism

B . Reverse central dogma

C . Central dogma

D . More than one option is correct

Solution:

It is the case of reverse central dogma which is also known as teminism because it is discovered by Temin & Baltimore in RSV.

Correct Answer : D

19. DNA exists in a double-stranded form whereas RNA is mainly a single stranded molecule. What is the likely reason for DNA being double stranded?

A . RNA strands cannot form base pairs.

B . Double stranded DNA is a more stable structure.

C . DNA cannot exist in the single stranded form.

D . It is easier to replicate double stranded DNA than single stranded RNA.

Solution:

Double stranded DNA is much more stable than single stranded RNA and this helps to protect our genetic code.

Correct Answer : B

20. Protein synthesis in an animal cell occurs

A . only on the ribosomes present in cytosol

B . only on ribosome attached to the nuclear envelope and endoplasmic reticulum

C . on ribosome present in the nucleolus as well as in cytoplasm

D . on ribosomes present in cytoplasm as well as in mitochondria.

Solution:

The mitochondria contain its own set of ribosomes which synthesize proteins, so protein synthesis occurs both in mitochondria and cytoplasm.

Correct Answer : D