TRB PG Assistant - Genes and chromosomes – chromatin, euchromatin, heterochromatin, giant chromosomes Online Test (MCQ Quiz)

1. What is the fundamental unit of heredity?

A) Cell B) Gene C) Protein D) Organelle

2. Which of the following is NOT a component of a chromosome?

A) DNA B) Proteins (histones) C) RNA D) Centromere

3. The complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells is called:

A) Nucleolus B) Cytoplasm C) Chromatin D) Ribosome

4. Which type of chromatin is generally transcriptionally active and loosely packed?

A) Heterochromatin B) Euchromatin C) Metachromatin D) Parachromatin

5. Heterochromatin is characterized by:

A) Loose DNA packing and high gene activity B) Dense DNA packing and low gene activity C) The presence of only RNA D) Absence of histone proteins

6. Which of the following is a function of euchromatin?

A) Preventing DNA replication B) Facilitating gene expression C) Condensing the chromosome during mitosis D) Sealing the nuclear envelope

7. Constitutive heterochromatin is typically found:

A) Only during S phase of the cell cycle B) In regions that are always condensed C) In regions that are actively transcribed D) Throughout the entire nucleus during interphase

8. Facultative heterochromatin:

A) Remains condensed throughout the cell cycle B) Can change its condensation state depending on cellular needs C) Is transcriptionally active D) Is never found in eukaryotic cells

9. The centromere region of a chromosome is typically rich in:

A) Euchromatin B) Telomeres C) Heterochromatin D) Genes encoding ribosomal RNA

10. Which of the following is a characteristic of heterochromatin compared to euchromatin?

A) More accessible to transcription factors B) Undergoes replication earlier in S phase C) Undergoes replication later in S phase D) Less likely to be associated with DNA methylation

11. Giant chromosomes, such as polytene chromosomes, are formed by:

A) Fusion of multiple chromosomes B) Repeated rounds of DNA replication without cell division C) Condensation of chromatin into a single strand D) Degradation of histone proteins

12. Polytene chromosomes are commonly found in:

A) Mammalian somatic cells B) Yeast cells C) Salivary glands of Drosophila larvae D) Bacterial cells

13. The characteristic 'puffs' or 'balbiani rings' observed in polytene chromosomes represent:

A) Regions of tightly condensed heterochromatin B) Sites of active gene transcription C) Centromeric regions D) Telomeric regions

14. Which type of giant chromosome exhibits a lampbrush appearance?

A) Polytene chromosomes B) Lampbrush chromosomes C) B-chromosomes D) Sex chromosomes

15. Lampbrush chromosomes are typically found during which stage of meiosis?

A) Anaphase I B) Telophase I C) Prophase I (specifically diplotene stage) D) Metaphase II

16. The loops extending from the central axis of lampbrush chromosomes are sites of:

A) DNA replication B) Protein synthesis C) RNA synthesis (transcription) D) Chromosome condensation

17. The term 'chromatin' refers to the complex of:

A) DNA and RNA B) DNA and proteins C) RNA and proteins D) Lipids and carbohydrates

18. Histones are a class of proteins that are primarily involved in:

A) DNA replication B) RNA transcription C) Packaging and condensing DNA D) Cellular respiration

19. Which of the following is a key feature of heterochromatin?

A) High gene density B) Early replication timing C) Underrepresentation of repetitive DNA sequences D) Late replication timing

20. Euchromatin is generally associated with:

A) Late DNA replication B) High levels of DNA methylation C) Open chromatin structure D) Transcriptional silencing

21. The formation of polytene chromosomes involves multiple rounds of:

A) Mitosis B) Meiosis C) Endoreduplication (DNA replication without cytokinesis) D) Apoptosis

22. The banding patterns observed in Giemsa-stained polytene chromosomes are related to:

A) The distribution of euchromatin and heterochromatin B) The location of centromeres C) The number of DNA replication rounds D) The presence of RNA polymerase

23. In lampbrush chromosomes, the axial structure consists primarily of:

A) Single-stranded DNA B) Double-stranded DNA with associated proteins C) Single-stranded RNA D) Ribosomes

24. The functional significance of the lampbrush structure is to:

A) Maximize DNA replication efficiency B) Facilitate rapid chromosome segregation C) Increase the surface area for gene transcription D) Compact the genome for storage

25. Which of the following is a type of heterochromatin that is present in all cells of an organism and is replicated late?

A) Facultative heterochromatin B) Constitutive heterochromatin C) Euchromatin D) Interchromatin

26. The Barr body, found in the nuclei of female mammals, is an example of:

A) Euchromatin B) Constitutive heterochromatin C) Facultative heterochromatin D) A polytene chromosome

27. The process of 'chromosome puffing' in polytene chromosomes indicates:

A) Chromosome breakage B) Gene silencing C) Active gene expression D) DNA repair

28. The structural organization of chromatin, including euchromatin and heterochromatin, is crucial for:

A) Protein synthesis B) Energy production C) Regulation of gene expression D) Cellular movement

29. Which of the following terms describes the DNA-protein complex that makes up chromosomes?

A) Nucleosome B) Chromatid C) Chromatin D) Centrosome

30. The euchromatic regions of a chromosome are typically:

A) Rich in repetitive DNA sequences B) Undergoing late DNA replication C) Deacetylated histones and accessible to transcription machinery D) Highly condensed and transcriptionally silent

31. Heterochromatin is often characterized by:

A) Acetylated histones B) Hypomethylated DNA C) Enriched repetitive DNA sequences D) High gene activity

32. Giant chromosomes like polytene chromosomes allow for:

A) Rapid cell division B) Detailed observation of gene activity C) Reduced metabolic rate D) Increased genome stability

33. In lampbrush chromosomes, the lateral loops are extensions of the axial fiber that are actively engaged in:

A) DNA replication B) mRNA synthesis C) Protein translation D) Chromosome condensation

34. The telomeres, regions at the ends of eukaryotic chromosomes, are typically composed of:

A) Euchromatin B) Heterochromatin C) Centromeric DNA D) Ribosomal DNA

35. Which of the following is a consequence of the tightly packed nature of heterochromatin?

A) Increased rate of DNA mutation B) Reduced accessibility to DNA repair enzymes C) Enhanced gene transcription D) Earlier replication during S phase

36. The transformation of euchromatin to heterochromatin can lead to:

A) Gene activation B) Transcriptional silencing C) Increased DNA replication D) Formation of nucleoli

37. Polytene chromosomes are an example of which phenomenon?

A) Chromosomal aberration B) Endopolyploidy C) Aneuploidy D) Polyploidy

38. The chromomeres, visible as bead-like structures in chromosomes, are more prominent in:

A) Condensed mitotic chromosomes B) Interphase nuclei C) Lampbrush chromosomes D) Polytene chromosomes

39. Which histone modification is generally associated with active transcription in euchromatin?

A) Histone methylation B) Histone ubiquitination C) Histone acetylation D) Histone phosphorylation

40. Heterochromatin plays a role in maintaining genome stability by:

A) Promoting recombination B) Preventing the formation of aberrant DNA structures C) Increasing gene expression D) Facilitating DNA repair

41. The specific banding pattern of chromosomes, observable in both polytene and mitotic chromosomes, is often used for:

A) Determining cell size B) Identifying chromosomal abnormalities C) Measuring gene expression levels D) Calculating the rate of DNA replication

42. Which component of chromatin is primarily responsible for the basic structure of the nucleosome?

A) Histone H1 B) Non-histone proteins C) Core histones (H2A, H2B, H3, H4) D) DNA polymerase

43. The transition from a decondensed euchromatic state to a condensed heterochromatic state is often mediated by:

A) Histone deacetylases B) Histone acetyltransferases C) DNA ligase D) RNA polymerase

44. Polytene chromosomes are formed by endomitosis, which is a process where:

A) The cell divides after DNA replication B) DNA replicates but the cell does not divide C) Chromosomes fuse together D) Chromosomes break apart

45. The 'puffs' in polytene chromosomes are regions where:

A) DNA is highly condensed B) Transcription is occurring C) DNA replication is stalled D) Histone proteins are being removed

46. Lampbrush chromosomes are characterized by extensive looping, which facilitates:

A) DNA repair B) Gene silencing C) Transcription of specific genes D) Chromosome condensation

47. The differential condensation of chromatin into euchromatin and heterochromatin is a key mechanism for:

A) Cellular respiration B) Cell signaling C) Cellular differentiation and development D) Cell motility

48. Which of the following is NOT a characteristic of heterochromatin?

A) Late replication B) Transcriptional silencing C) Early replication D) Presence of repetitive DNA sequences

49. The study of giant chromosomes has been instrumental in understanding:

A) Mitochondrial function B) The relationship between chromosome structure and gene activity C) The process of photosynthesis D) The mechanism of viral replication

50. Which type of chromatin is more sensitive to DNase I digestion, indicating a more open structure?

A) Heterochromatin B) Euchromatin C) Constitutive heterochromatin D) Facultative heterochromatin

Genes and chromosomes – chromatin, euchromatin, heterochromatin, giant chromosomes - Online Test

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