Molecular Basis of Inheritance Mock Test – Class 12 Biology

1. 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?

2. A mutation replaces many positively charged lysine and arginine residues of core histones with electrically neutral residues, while the DNA sequence remains unchanged. What is the most direct predicted effect?

3. A eukaryotic cell forms normal nucleosomes, but proteins required for higher levels of chromatin packaging are experimentally made non-functional. Which effect is most directly expected?

4. Match each item with its role in the Hershey-Chase experimental logic. Each Column II entry is used once.

5. A genome-sequencing project successfully determines the nucleotide sequence of every cloned fragment, but all information about sequence overlaps between fragments is lost. Which task becomes most directly impaired?

6. A proposed primitive biological system contains only one major nucleic-acid type. The molecule can preserve sequence information and can also catalyse certain reactions needed by the system. Which interpretation best fits the RNA-world hypothesis?

7. Cells with fully -labelled DNA undergo one generation in medium, producing only hybrid DNA. They are then transferred back to medium for one more replication. What DNA classes are expected after that replication?

8. Suppose both strands of one DNA transcription unit are independently used as templates. What problem is most directly predicted from their sequence relationship?

9. When lactose and glucose availability are considered in the lac operon, which statement is most accurate?

10. A double-stranded DNA molecule contains nucleotide residues in total, and the ratio is . How many residues of each base are present?

11. A germ-line mutation inserts exactly nucleotides within the amino-acid-coding region of a gene. The inserted triplet is a sense codon and no existing start or stop signal is disrupted. Which outcome is most consistent with the molecular principles?

12. Two men being considered in a paternity case are monozygotic twins. The child's nonmaternal VNTR bands are compatible with the DNA fingerprint shared by both twins. What can classical VNTR-based fingerprinting conclude?

13. Along a chromatin segment, electron microscopy reveals regularly spaced bead-like structures connected by stretches of DNA. If each bead contains DNA associated with a histone octamer, the observation most strongly indicates:

14. The supplied genetic-code information states UAU = tyrosine and UAA = stop. A single-base substitution changes an mRNA codon from UAU to UAA within the middle of a coding region. What is the most direct predicted consequence?

15. Avery-MacLeod-McCarty and Hershey-Chase used different organisms and different experimental approaches. Which shared conclusion is strengthened when their results are considered together?

16. Translation begins at the first codon of the sequence . Which grouping is consistent with a contiguous triplet code?

17. The relation describes the combinatorial capacity of a triplet code built from four RNA bases. Which interpretation of this relation is valid?

18. Consider the following statements about processing of eukaryotic hnRNA.
I. The primary transcript may contain both exon and intron sequences.
II. Splicing removes introns and joins exon-derived regions.
III. Tailing adds methyl guanosine triphosphate to the end.
IV. Capping modifies the end, whereas an adenylate tail is added at the end.

19. Three experiments are summarised below.

Which interpretation best reflects the progression of evidence?

20. Consider the following statements about the nitrogen isotope used in the Meselson-Stahl experiment.
I. is heavier than .
II. was used to make DNA of greater density.
III. was detected by measuring radioactive decay from DNA.
IV. The experiment distinguished DNA populations using density-gradient centrifugation.

21. Evaluate the following statements concerning split genes and RNA-world interpretation.
I. Split genes contain exon regions interrupted by introns.
II. Introns can be interpreted as ancient features of genome organisation.
III. The existence of introns alone proves the exact molecular sequence by which the earliest life evolved.
IV. RNA splicing is compatible with the idea that RNA-dependent processes have deep evolutionary significance.

22. In a eukaryotic nucleus, RNA polymerases I and III are selectively inhibited while RNA polymerase II remains active. Which combined prediction is most appropriate?

23. A selective inhibitor blocks eukaryotic RNA polymerase II while RNA polymerases I and III remain functional. Which combined outcome is most consistent with this condition?

24. A tRNA normally carries amino acid X and has an anticodon complementary to codon P. Its anticodon mutates so that the tRNA now recognises codon Q, but it continues to carry amino acid X. If codon Q normally specifies amino acid Y, what can occur?

25. A polynucleotide is described from left to right. Its left terminus has a free phosphate attached to the carbon, and its right terminus has a free hydroxyl group on the carbon. What is the direction of the chain as described?

26. Consider the following statements about the genetic code.
I. Codons are read successively without punctuation between neighbouring triplets.
II. The meaning of most codons is shared across widely different organisms.
III. The code is absolutely identical in every known cellular and organellar system.
IV. Mitochondrial codons and some protozoan systems provide exceptions to complete universality.

27. DNA in eukaryotic chromatin is negatively charged because of its phosphate groups, whereas histones are rich in positively charged amino acids such as lysine and arginine. Which consequence follows most directly from this charge relationship?

28. Researchers compare VNTR allele frequencies across several geographically separated populations to estimate patterns of genetic diversity. Which feature of the markers makes this application possible?

29. During genome assembly, one sequenced fragment overlaps equally well with two different assembled regions because both regions contain the same repetitive sequence. No unique polymorphic marker or chromosome anchor is present in the fragment. What is the most defensible conclusion?

30. 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?

31. A newly discovered virus uses single-stranded RNA as its hereditary material. Its mutation rate is much higher than that of a comparable DNA-based system, but it still transmits genetic information successfully between generations. Which interpretation best fits the standard DNA-RNA comparison?

32. 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.

33. 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?

34. Two mutants of the same gene show the following results.

Which interpretation best distinguishes P from Q?

35. Reported Human Genome Project observations include about human genes, an average gene size of approximately , a genome size of about , and less than of the genome as protein-coding. Multiplying the first two values gives about bases, or roughly of the genome. Why does this not necessarily contradict the stated protein-coding fraction?

36. Four hypothetical molecules are evaluated as possible long-term hereditary material.

Which molecule best satisfies the standard criteria for genetic material?

37. 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?

38. A DNA duplex contains , and its G-C content is . How many hydrogen bonds hold the paired bases together?

39. Four insertion or deletion events occur within coding regions, away from start and stop signals.

Assuming no additional mutations, which grouping of effects is expected from triplet reading?

40. Two structural-gene organisations are compared.

P and Q are best described as:

41. Escherichia coli DNA is fully labelled with and then allowed to replicate for three generations in . Under semiconservative replication, which pair correctly gives the fraction of DNA molecules that are hybrid and the fraction of all individual DNA strands that still contain ?

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

Which inference is best supported?

43. A bacterial transcriptional arrangement contains three successive polypeptide-coding cistrons that can be represented within a common transcript. Which description best captures this organisation?

44. Two linear double-stranded DNA fragments, P and Q, are each long. P contains GC base pairs, while Q contains GC base pairs. Which comparison is correct?

45. DNA polymerase is supplied with a correct DNA template and all four deoxyribonucleoside monophosphates, but no deoxyribonucleoside triphosphates are available. Which outcome is most directly expected?

46. 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?

47. A molecular unit contains adenine joined to deoxyribose, and the sugar is also linked to phosphate. This complete unit is a:

48. Assertion: Complementarity of the two DNA strands provides a structural basis for semiconservative replication.
Reason: Each parental strand can act as a template for synthesis of a complementary daughter strand.

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

50. 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?