Molecular Basis of Inheritance Mock Test – Class 12 Biology

1. A DNA construct can be transcribed from its promoter after entering a bacterial cell, but it is progressively lost from the population because it is not copied as cells divide. Adding a functional [blank] would most directly correct the replication defect.

2. A mutation deletes most of the UTR of a eukaryotic mRNA but leaves the translated region, its stop codon and the encoded amino-acid sequence intact. Which outcome is most appropriate?

3. A coding region undergoes an insertion of exactly nucleotides between two existing codons. Assuming no stop codon is introduced by the inserted triplet, which outcome is most consistent with triplet reading?

4. Promoter recognition occurs normally in a bacterial transcription system, but the supply of ribonucleoside triphosphates is suddenly exhausted during elongation. What is the most direct consequence?

5. Which process is essential for hereditary continuity but is not itself part of the standard expression sequence represented by the central dogma?

6. Two genes encode exactly the same short polypeptide but differ at several nucleotide positions within their coding regions. No insertion, deletion or stop-codon change is present. Which explanation is most directly consistent with the genetic code?

7. A hypothetical polynucleotide retains deoxyribose and phosphate throughout its backbone, but every thymine base is replaced by uracil. Consider the following statements.
I. Its pentose feature remains DNA-like.
II. Its thymine-to-uracil change is RNA-like.
III. The uracil substitution alone makes the entire polymer ordinary RNA.

8. Assertion: Transfer of biological sequence information from protein directly back into DNA is part of the standard central-dogma pathway.
Reason: The usual information flow is , while an step occurs in some viruses.

9. A regulatory protein normally acts as a repressor by binding operator P but cannot bind operator Q because Q has a different sequence. A mutation converts Q into a sequence identical to P without changing the adjacent promoter or structural gene. What new effect becomes plausible?

10. Evaluate the following statements about bonds in nucleic-acid structure.
I. The nitrogenous base is attached to the carbon of the pentose by an N-glycosidic linkage.
II. Phosphate can be attached to the carbon of the sugar by a phosphoester linkage.
III. Adjacent nucleotides in a strand are connected through phosphodiester linkages.
IV. Hydrogen bonds between complementary bases form the covalent sugar-phosphate backbone of one strand.

11. Use the following arrangement. In a double-stranded DNA region, one strand acquires a local chemical alteration while the complementary strand at the same positions remains intact. Which feature of the duplex can most directly assist restoration of the original sequence information?

12. Before concluding from a DNase-treated sample that DNA is the transforming principle, investigators verify that the DNase preparation actually degrades DNA under the experimental conditions. Why is this control important?

13. Match each bacterial transcription component with its principal role. Each Column II entry is used once.

14. In the Taylor experiment with Vicia faba root cells, chromosomes are allowed one replication cycle in tritiated thymidine and then a second replication cycle in non-radioactive medium. Which autoradiographic pattern is most consistent with semiconservative replication?

15. Escherichia coli is grown for many generations in medium containing . Before transfer to , what is expected for its DNA?

16. An mRNA contains two AUG codons. The first AUG functions as the initiation codon, while the second AUG occurs later within the established reading frame and specifies an internal methionine. A mutation changes only the second AUG to a codon for valine. What is the most direct effect?

17. In a classical DNA-fingerprinting experiment, DNA is isolated but the restriction-digestion step is accidentally omitted before electrophoresis. Which consequence is most directly expected?

18. Three elements of a transcription unit are listed.
P. Promoter
Q. Structural gene
R. Terminator
For transcription proceeding through the structural gene in its normal orientation, the most appropriate order is:

19. A bacterial transcriptional unit contains several structural genes whose products participate in utilisation of the same nutrient. When the nutrient becomes relevant, transcription of the genes changes coordinately rather than independently. This pattern is most consistent with:

20. Assertion: A DNA strand has a chemically defined end and end even if its base sequence happens to read symmetrically.
Reason: Polynucleotide polarity arises from the arrangement of sugar-phosphate linkages and the chemically different terminal groups, not from whether the base sequence itself is symmetric.

21. Escherichia coli completes one generation in approximately under the stated experimental conditions. DNA is sampled and after transfer from medium to medium. These samples correspond approximately to:

22. A mutant small ribosomal subunit is unable to associate correctly with mRNA, while the large subunit and its rRNA-mediated peptide-bond catalytic activity remain intact. What is the most direct consequence?

23. In a bacterial transcription experiment, sigma factor is present long enough for RNA polymerase to recognise the promoter and initiate RNA synthesis. Sigma is then experimentally removed, but the core polymerase remains intact and nucleotide substrates are abundant. What is the most likely immediate outcome?

24. Ribosomal subunits assemble normally on an mRNA, and charged tRNAs still recognise their codons. However, the catalytic rRNA responsible for peptide-bond formation is selectively inactivated. What is the most direct outcome?

25. A DNA profile recovered from an object matches a person's VNTR profile at every locus examined. Which additional claim is not justified by that match alone?

26. A lac repressor is mutated so that it can never bind inducer and therefore remains capable of operator binding. In the same strain, however, the operator is independently mutated so that this repressor cannot bind it. The promoter and structural genes are functional. Which outcome is most likely?

27. Escherichia coli DNA is stated to have an extended length of approximately . Using , its DNA contains approximately:

28. The Human Genome Project uses polymorphic markers in genome mapping, while DNA fingerprinting uses highly variable repetitive loci for individual comparison. What principle links these two applications?

29. A lac-operon mutant produces normal permease and transacetylase, and repression is relieved normally in the presence of inducer. However, lactose enters the cell but is not efficiently hydrolysed into glucose and galactose. The defective gene is most likely:

30. Four events of bacterial transcription are listed.
P. Promoter recognition with the initiation-associated factor
Q. RNA-chain elongation by the polymerase
R. Termination at the end of the transcription unit
S. Release of the completed transcript
The most appropriate order is:

31. Samples are collected from one individual and analysed successfully at the same fingerprinting loci.

What should replace the question marks under the stated conditions?

32. An mRNA segment is . The DNA template strand that produced it, written opposite the RNA in the transcriptional orientation, is:

33. A cell enters S phase and duplicates a DNA region containing a gene that is not being expressed. Later, the same gene becomes active and only its information is copied into RNA. This contrast illustrates that:

34. A double-stranded DNA molecule contains . Irrespective of its G-C content, how many purine bases are present in the complete molecule?

35. Study the approximate nucleic-acid sizes shown below.

Using only the scale of the two cellular genomes, the haploid human value is approximately how many times the Escherichia coli value?

36. Escherichia coli contains about of DNA and completes replication in approximately . The effective whole-genome duplication rate required over that interval is closest to:

37. In a classical fingerprinting experiment, a positive-control DNA known to contain the probe target fails to produce any autoradiographic band, and the test sample also shows no bands. Which interpretation is most appropriate?

38. Assertion: Genetic material should be chemically stable but not absolutely incapable of change.
Reason: Complete absence of heritable variation would remove the mutational source needed for evolutionary change.

39. Griffith and Avery-MacLeod-McCarty studied the same general phenomenon but reached different levels of conclusion. Which comparison is accurate?

40. Equal very small DNA samples are tested under two conditions.

Which inference is best supported?

41. A supplied codon table shows that both UUU and UUC specify phenylalanine. Two otherwise identical mRNAs differ only by having UUU in one and UUC in the other at the same codon position. Both produce phenylalanine there. This observation illustrates:

42. The coding strand of a transcription unit is . What RNA sequence is produced, assuming this region is transcribed in the stated orientation?

43. A mutant release factor can recognise UAA and UAG normally but cannot recognise UGA. An mRNA contains UGA as its normal stop codon and a downstream in-frame UAA. What is the most likely outcome?

44. Normal beta-globin coding DNA contains the triplet , corresponding to glutamate. A single-base substitution changes it to , whose mRNA counterpart is and specifies valine. Which information-flow chain describes the mutation?

45. Consider the following statements about charged and uncharged tRNA.
I. A charged tRNA carries an amino acid at its acceptor end.
II. An uncharged tRNA lacks the amino acid that should be delivered during translation.
III. Charging changes the tRNA anticodon into the corresponding mRNA codon.
IV. Charged tRNAs provide amino-acid-bearing substrates for ribosomal protein synthesis.

46. A crime-scene profile is compared with three individuals.

Which conclusion stays within what the fingerprint alone supports?

47. In a triplet code using the four bases A, U, G and C, the first position of a codon is fixed as A while the second and third positions may each contain any of the four bases. How many different codons satisfy this condition?

48. A transcription unit has the coding strand . A mutation reverses promoter orientation so that the opposite DNA strand becomes the coding strand for transcription through the same region. Which RNA sequence would now correspond to the newly designated coding strand, written ?

49. A mutant DNA polymerase operates at approximately the normal replication speed but incorporates incorrect nucleotides much more frequently. If the errors persist in the DNA, the most important consequence is:

50. Two polymorphic markers are being considered for human-genome analysis.

Which interpretation is correct?