15 extra multiple-choice questions for Molecular Genetics (12th Standard Zoology, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
Who coined the term "gene" in 1909 to refer to the discrete determiners of inherited characteristics?
- A. Wilhelm JohannsenCorrect
- B. Gregor Mendel
- C. Walter Sutton
- D. George Beadle
Explanation. The Danish biologist Wilhelm Johannsen coined the term "gene" in 1909, whereas Gregor Mendel had previously referred to these hereditary units as "factors".
Q2
Which organism was used by George Beadle and Edward Tatum in the early 1940s to propose the one gene-one enzyme hypothesis?
- A. Escherichia coli
- B. Neurospora crassaCorrect
- C. Streptococcus pneumoniae
- D. Drosophila melanogaster
Explanation. Beadle and Tatum used Neurospora crassa, the red bread mould, to propose that one gene controls the production of a single enzyme.
Q3
In the transformation experiments of Avery, Macleod, and McCarty, the transforming ability of the heat-killed S-strain extract was lost only when treated with which enzyme?
- A. Protease
- B. RNase
- C. DNaseCorrect
- D. Amylase
Explanation. Digestion of the extract with DNase inhibited the transformation of R-strain bacteria into the virulent S-strain, demonstrating that DNA is the transforming substance.
Q4
Which radioactive isotopes were used by Alfred Hershey and Martha Chase in 1952 to selectively label viral proteins and DNA?
- A. 14C and 15N
- B. 3H and 14C
- C. 35S and 32PCorrect
- D. 15N and 32P
Explanation. Hershey and Chase used radioactive sulphur-35 to label proteins and radioactive phosphorus-32 to label DNA during bacteriophage infection of Escherichia coli.
Q5
What is the primary chemical difference between the pentose sugar ribose found in RNA and deoxyribose found in DNA?
- A. Deoxyribose has one less carbon atom than ribose
- B. Deoxyribose has one less oxygen atom than riboseCorrect
- C. Deoxyribose has one more hydroxyl group than ribose
- D. Deoxyribose is a hexose sugar while ribose is a pentose sugar
Explanation. Deoxyribose and ribose are both five-carbon sugars, but deoxyribose lacks one oxygen atom compared to ribose.
Q6
A nucleoside is converted into a nucleotide when a phosphate group is covalently attached to which carbon of the pentose sugar?
- A. 1' carbon
- B. 2' carbon
- C. 3' carbon
- D. 5' carbonCorrect
Explanation. A nucleoside consists of a nitrogenous base linked to the 1'-carbon of a sugar, and becomes a nucleotide upon addition of a phosphate to the 5'-carbon.
Q7
Who first coined and used the term "RNA world" in 1986 to hypothesize that RNA was the first genetic material on Earth?
- A. Walter GilbertCorrect
- B. Leslie Orgel
- C. Francis Crick
- D. Carl Woese
Explanation. Walter Gilbert first used the term "RNA world" in 1986, although Leslie Orgel, Francis Crick, and Carl Woese had independently proposed the concept earlier.
Q8
Approximately how many base pairs of DNA are wrapped around a single histone octamer to form a typical nucleosome in eukaryotes?
- A. 100 bp
- B. 140 bp
- C. 200 bpCorrect
- D. 340 bp
Explanation. In eukaryotes, a typical nucleosome contains 200 base pairs of DNA helix wrapped around a histone octamer.
Q9
The 30 nm chromatin fiber is stabilized by H1 interactions and forms a solenoid structure containing how many nucleosomes per turn?
- A. Two nucleosomes
- B. Four nucleosomes
- C. Six nucleosomesCorrect
- D. Eight nucleosomes
Explanation. The folding of nucleosome chains into a 30 nm solenoid structure is stabilized by H1 interactions and has six nucleosomes per turn.
Q10
Given that Escherichia coli has approximately 4.6 x 10^6 base pairs and replicates in 18 minutes, what is its average rate of polymerization?
- A. 500 bp/sec
- B. 1000 bp/sec
- C. 2000 bp/secCorrect
- D. 5000 bp/sec
Explanation. E. coli replicates its genome of 4.6 million base pairs within 18 minutes, requiring an average polymerization speed of roughly 2000 base pairs per second.
Q11
In prokaryotes, which specific subunit of the RNA polymerase holoenzyme is responsible for recognizing the promoter sequence on DNA?
- A. Alpha subunit
- B. Beta subunit
- C. Omega subunit
- D. Sigma subunitCorrect
Explanation. The prokaryotic RNA polymerase core enzyme synthesizes RNA, while the transiently associated sigma subunit is responsible for promoter site recognition.
Q12
What is the name of the AT-rich promoter region found in eukaryotes, which is also referred to as the Goldberg-Hogness box?
- A. Pribnow box
- B. TATA boxCorrect
- C. Shine-Dalgarno sequence
- D. Solenoid box
Explanation. The TATA box is an AT-rich eukaryotic promoter region, whereas the corresponding prokaryotic region is known as the Pribnow box.
Q13
The point mutation causing sickle cell anemia involves a single base substitution in the sixth codon of the beta-globin gene, changing it from:
- A. GTG to GAG
- B. GAG to GTGCorrect
- C. GUG to GAG
- D. GAG to GUG
Explanation. Sickle cell anemia is caused by a point mutation that changes the sixth codon of the beta-globin gene from GAG to GTG, substituting glutamic acid with valine.
Q14
What is the name of the prokaryotic ribosome binding site located at the 5' end of mRNA that base-pairs with 16S rRNA?
- A. TATA box
- B. Pribnow box
- C. Shine-Dalgarno sequenceCorrect
- D. Kozak sequence
Explanation. The Shine-Dalgarno (S-D) sequence is a ribosome binding site on prokaryotic mRNA that base-pairs with 16S rRNA to facilitate translation initiation.
Q15
Which is the largest known human gene, consisting of approximately 2.4 million bases?
- A. Insulin
- B. Hemoglobin
- C. DystrophinCorrect
- D. Actin
Explanation. Dystrophin is the largest known human gene, spanning 2.4 million bases, while the average human gene consists of 3000 bases.
Frequently asked questions
How many MCQs are there in Molecular Genetics?
This chapter has 15 book-back multiple-choice questions, each with the correct answer and a step-by-step explanation.
Are these 12th Standard Zoology MCQs free to practise online?
Yes. Every question, answer and explanation here is free, and you can also take them as a timed practice test.
Where can I find the Molecular Genetics book-back answers?
The correct option for each question is highlighted on this page with a worked explanation, plus a quick answer-key summary at the top.
