Exams › NEET › Biology › Molecular Basis of Inheritance
248 questions with worked solutions.
Q1. Which of the following is a transcription factor produced by a regulatory gene?
Answer: A repressor
A regulatory gene can produce a protein that affects transcription. A repressor is such a protein: it binds to DNA near a gene and blocks RNA polymerase, reducing transcription.
Q2. Which of the following combination is false?
Answer: A-G
A-T is a normal DNA base pair, and A-U is a normal RNA base pair. A-G is not a standard complementary pair, so it is the false combination.
Q3. Which scientist experimentally proved that DNA is the sole genetic material in bacteriophage?
Answer: Hershey and Chase
Hershey and Chase used bacteriophages labeled with radioactive phosphorus in DNA and radioactive sulfur in protein. Only the DNA label entered the bacterial cells and directed production of new phages, proving DNA is the genetic material.
Answer: 2.2 meters
The DNA length is the number of base pairs times the distance between adjacent base pairs. Using 0.34 nm per bp and 6.6 × 10^9 bp gives 2.244 × 10^9 nm, which is about 2.2 m after unit conversion.
Q5. Which of the following RNAs should be most abundant in animal cell?
Answer: r-RNA
rRNA is the most abundant RNA in animal cells because ribosomes are extremely numerous and each ribosome contains large amounts of rRNA. mRNA, tRNA, and miRNA are present in much smaller amounts relative to rRNA.
Q6. The final proof for DNA as the genetic material came from the experiments of:
Answer: Hershey and Chase
Hershey and Chase used bacteriophages labeled with radioactive phosphorus and sulfur to track which molecule entered bacteria. Their results showed DNA was the genetic material, providing the final confirmation.
Q7. Which one of the following is not applicable to RNA?
Answer: Chargaff’s rule
Chargaff’s rule describes the base composition relationships in double-stranded DNA, where adenine equals thymine and guanine equals cytosine. RNA does have phosphate-sugar ends, nitrogenous bases, and can form complementary base pairs, but it does not generally obey Chargaff’s rule.
Answer: 17% A, 33%, T 33%
In double-stranded DNA, cytosine pairs with guanine, so %C = %G = 17%. That leaves 66% for adenine and thymine, which must be equal, so each is 33%.
Q9. Which of the following statements is correct?
Answer: Adenine pairs with thymine through two H-bonds
In DNA, adenine pairs specifically with thymine, and this pair is stabilized by two hydrogen bonds. The three-hydrogen-bond pairing belongs to guanine and cytosine.
Answer: UAGAC
During transcription, RNA is built complementary to the DNA template strand. Applying the pairing rules to ATCTG gives UAGAC, which matches option B.
Q11. DNA fragments are:
Answer: Negatively charged
DNA has a sugar-phosphate backbone, and the phosphate groups are deprotonated under normal biological conditions. That gives DNA an overall negative charge.
Q12. The unequivocal proof of DNA as the genetic material came from the studies on a
Answer: bacterial virus
The decisive evidence came from bacteriophages, which infect bacteria and allowed researchers to separate viral DNA from protein. Experiments showed that the DNA entered the host and directed production of new viruses, proving DNA was the genetic material.
Q13. Transformation was discovered by:
Answer: Griffith
Griffith discovered bacterial transformation in his experiments with Streptococcus pneumoniae. He showed that a non-virulent strain could be transformed into a virulent one by exposure to material from heat-killed virulent bacteria.
Q14. Anticodon is an unpaired triplet of bases in an exposed position of
Answer: tRNA
The anticodon is a three-base sequence found on transfer RNA, where it base-pairs with the complementary codon on mRNA during protein synthesis. This pairing helps ensure the correct amino acid is added to the growing polypeptide chain.
Q15. Initiation codon of protein synthesis (in eucaryotes) is
Answer: AUG
In eukaryotes, translation typically starts at the AUG codon, which codes for methionine. The initiator tRNA pairs with AUG to establish the correct reading frame for protein synthesis.
Q16. What base is responsible for hot spots for spontaneous point mutations?
Answer: 5-methylcytosine
5-methylcytosine is prone to spontaneous deamination, producing thymine and creating a T:G mismatch. This makes methylated CpG sites common mutation hot spots.
Answer: Regulator genes
Regulator genes produce products that control the transcription of other genes, especially structural genes in an operon or gene network. They act as switches or modulators rather than encoding the structural proteins themselves.
Q18. Which step of translation does not consume a high energy phosphate bond?
Answer: Peptidyl-transferase reaction
The peptidyl-transferase reaction forms the peptide bond between amino acids on the ribosome, and it does not directly use a high-energy phosphate bond. The energy for this bond comes from the aminoacyl-tRNA linkage created during amino acid activation, which does consume ATP.
Q19. DNA elements which can shift their position are called
Answer: transposons
Transposons are mobile DNA sequences that can change their position in the genome, so they are often called “jumping genes.” Exons, introns, and cistrons do not refer to movable DNA elements.
Q20. Three codons causing chain termination are
Answer: UAG, UGA, UAA
The three termination codons in mRNA are UAG, UGA, and UAA. They signal the ribosome to stop translation, so the option containing exactly these three is correct.