8 Eukaryotic Chromosomes

1. What is the primary structural difference between the gene for the muscle protein titin and histone genes regarding their organization?

Histone genes are composed entirely of SINEs, while titin is composed of LINEs.
Titin contains an exceptionally high number of introns, while histone genes contain none.
Titin is found only in heterochromatin, while histone genes are in euchromatin.
Histone genes have a higher ratio of introns to exons than the titin gene.

2. Which organism’s genome is characterized by genes being closely packed together with very little ‘excess’ DNA?

Mus musculus
Saccharomyces cerevisiae
Oryza sativa
Homo sapiens

3. Which statement regarding the Alu element in the human genome is correct based on the provided material?

It accounts for 21% of the total human DNA sequence content.
It is a type of SINE (Short Interspersed Element) with approximately 1 million copies.
It is a protein-coding gene that regulates chromosomal stability.
It is a LINE (Long Interspersed Element) measuring 6−8 kb in length.

4. In the structural diagram of a chromosome, what role is attributed to ‘Unique sequences (genes)’?

They are the sites where DNA replication originates.
They ensure the replication of the chromosome ends.
They are the specific segments of DNA that carry hereditary information.
They are responsible for attaching the chromosome to the mitotic spindle.

5. Which specific type of transposable element accounts for approximately 1 million copies in the human genome and belongs to the SINEs category?

Simple sequence repeats (SSR)
L1 elements
HERV-K
Alu elements

6. Based on the Dewey et al. (2011) study of a family quartet, what prediction was made for the mother based on her genotype?

A specific required dose for blood thinners.
High risk for obesity and pulmonary embolism.
Inherited clotting mutation from her own father.
Risk for psoriasis, although yet to display symptoms.

7. How did the definition of a ‘gene’ change as our understanding of molecular biology progressed?

It broadened to include segments of DNA that produce functional RNA molecules as their final product.
It was redefined to include all 'junk DNA' as parts of larger genetic units.
It narrowed to include only sequences that contain both introns and exons.
It became limited strictly to the 1.5% of the genome that is translated into protein.

8. How does the ENCODE project’s findings challenge the traditional concept of ‘junk DNA’?

It revealed that at least 80% of the genome is biochemically active in at least one cell type.
It demonstrated that mutations in non-coding regions have no impact on human disease.
It showed that 'junk DNA' is actually composed entirely of essential telomeric repeats.
It proved that 90% of the genome codes for protein products in specific embryonic stages.

9. What percentage of the human genome is estimated to be functional in the regulation of gene expression (e.g., binding proteins, chromatin modifications)?

∼1.5%
∼60%
∼45%
∼20%

10. Which organism has the highest total number of genes, and how does this relate to biological complexity?

Rice (Oryza sativa); it shows there is only some correlation between gene number and complexity.
Mouse (Mus musculus); it suggests that mammals have reached a plateau of gene count.
Humans (Homo sapiens); it proves that the most complex organisms always have the most genes.
Yeast (Saccharomyces cerevisiae); it shows that single-celled organisms require the most genes for survival.

11. What is the defining characteristic of orthologous genes compared to paralogous genes?

Orthologs are found only in prokaryotes, while paralogs are unique to eukaryotes.
Orthologs are homologous genes found in different species, whereas paralogs are found in the same species.
Paralogs always retain the same function, while orthologs always evolve new functions.
Orthologs have identical sequences, while paralogs only share 50% similarity.

12. Which of the following describes the Hemoglobin β subunit gene’s organization?

It has 3 exons and 2 introns, where one intron contains more than 50% of the gene's DNA.
It lacks introns entirely because it must be expressed rapidly.
It is the largest gene in the human genome at 2.4 million base pairs.
It is primarily made of Alu elements that regulate its expression.

13. What is the primary characteristic of a pseudogene?

It is a gene that codes for RNA but has no protein product.
It is a gene that has exons but no introns.
It is a repetitive sequence such as a SINE or LINE element.
It resembles a functional gene but contains mutations that prevent its proper expression.

14. What role does the centromere play during eukaryotic cell division?

It acts as the primary site where DNA replication is initiated.
It protects the ends of the chromosome from degradation by exonucleases.
It provides a binding site for proteins that attach the chromosome to the mitotic spindle.
It codes for the histone proteins required for chromatin compaction.

15. What is the role of the ‘Origin of Replication’ in a chromosome?

It is the specific DNA sequence where DNA synthesis begins.
It is the region where the two sister chromatids are held together.
It ensures that the very ends of the chromosome are not lost during division.
It is the boundary between heterochromatin and euchromatin.

16. What significant discovery was made by ENCODE concerning single nucleotide changes identified in Genome Wide Association Studies (GWAS)?

Nearly all disease-associated SNPs are found in the 1.5% of the genome that codes for proteins.
Approximately 90% of these changes lie outside the protein-coding portion of genes.
Disease-associated SNPs are primarily located within centromeres and telomeres.
Only single-gene disorders can be identified through GWAS analysis.

17. Which of the following is a key finding regarding the transcriptional activity of the human genome according to the ENCODE project?

Approximately 60% of the genome is transcriptionally active, though most products are RNAs of unclear function.
The number of protein-coding genes was found to be much higher than previously thought, exceeding 100,000.
Transcriptional activity is only found in the telomeric and centromeric regions.
Transcription is limited strictly to the 1.5% of DNA that contains exons.

18. According to the human genome ‘Vital Statistics’, what is the mean number of exons per gene?

27,000
10.4
1
178

19. What is the significance of the (TxGy)n sequence found in eukaryotic chromosomes?

It represents the sequence of simple sequence repeats (SSR) that make up 3% of the genome.
It is the consensus sequence for the origin of replication in humans.
It comprises telomeres, ensuring that the ends of the chromosomes are fully replicated.
It is the sequence recognized by the mitotic spindle for chromosome attachment.

20. What distinguishes SINEs from LINEs in the human genome structure?

SINEs make up 21% of the genome, while LINEs make up only 13%.
LINEs are always located at the telomeres, while SINEs are at the centromeres.
LINEs are significantly longer (6-8 kb) compared to SINEs (100-300 bp).
SINEs contain the 'pol' gene for reverse transcriptase, while LINEs do not.

21. The ENCODE project identified approximately how many long noncoding RNAs (lncRNAs) in the human genome?

9,600
25,000
1.5 million
21,000

22. Based on the organization of human chromosome 22, which statement is true about its composition?

It contains exactly four genes within its 48×10^6 nucleotide pair length.
Its left arm contains mostly protein-coding genes in a highly compacted form.
It represents approximately 1.5% of the entire human genome.
It is composed of a single DNA molecule that is 3.2×10^9 nucleotide pairs long.

23. Which component of the human genome is described as a ‘nucleotide sequence closely resembling a functional gene but containing mutations that prevent proper expression’?

Ortholog
Intron
Pseudogene
Simple Sequence Repeat (SSR)

24. Comparing the gene density of E.coli to that of Homo sapiens, which statement accurately reflects the disparity in their genomic organization?

Both organisms share a similar gene density because they both utilize DNA as their primary hereditary material.
The gene density of humans is higher because human genes contain introns which increase the total genetic material.
E.coli has a gene density approximately 100 times higher than humans.
Humans possess a higher gene density due to having more genes (29,000) compared to E.coli (4,435).

25. Comparing Saccharomyces cerevisiae and human gene organization, what is a key difference in their non-coding DNA content?

Yeast genes are closely packed with little excess DNA, while human genes are interspersed with large amounts of non-coding 'junk' DNA.
Humans lack the regulatory DNA sequences that are prevalent in the yeast genome.
Yeast genomes have a higher percentage of 'junk DNA' than the human genome.
Yeast chromosomes lack centromeres, whereas human chromosomes have them.

26. What is the typical sequence repeat found in mammalian telomeres?

Poly-A tails
(AT)n
Simple Segmental Duplications
(TxGy)n

27. In the context of evolutionary biology, how are paralogous genes distinguished from orthologous genes?

Paralogous genes are found within the same species, whereas orthologous genes are found in different species.
Orthologous genes share sequence similarity, while paralogous genes do not share any detectable similarity.
Orthologous genes are only found in eukaryotes, while paralogous genes are specific to prokaryotes.
Paralogous genes always code for RNA, while orthologous genes always code for proteins.

28. Regarding the Intron/Exon organization of specific genes, which of the following is true for the muscle protein titin?

It contains 178 introns.
It has no introns, similar to histone genes.
It has only 3 exons, like the hemoglobin β subunit.
Its introns make up only 1.5% of its total DNA sequence

29. In the context of the ENCODE project, what was the significance of the 90% GWAS finding?

It proved that 90% of all human diseases are caused by mutations in the 1.5% protein-coding region.
It showed that most disease-associated genetic variations are located in regulatory or non-coding regions.
It confirmed that only 10% of the human genome has any biochemical function.
It discovered that 90% of the human population shares the exact same pseudogene mutations.

30. The ENCODE project findings challenged the traditional view of ‘junk DNA’. Which of the following statistics best supports this paradigm shift?

Approximately 90% of disease-associated SNPs are found within the protein-coding exons.
At least 80% of the human genome is biochemically active in at least one cell type.
The human genome contains approximately 21,000 protein-coding genes.
Exactly 1.5% of the genome encodes for proteins.

31. What is the primary role of ChIP-seq (Chromosome Immunoprecipitation-sequencing) as used in the ENCODE project?

To detect and map histone modifications across the genome.
To distinguish between orthologous and paralogous gene families.
To sequence the 1.5% of the genome that codes for proteins.
To determine the exact number of chromosomes in different eukaryotic species.

32. Which of the following describes the organization of the Ovalbumin gene?

It consists of 178 introns, making it the most complex gene in the genome.
It has 8 exons and 7 introns, where introns constitute 85% of the gene's DNA.
It is a rare example of a human gene that contains no introns.
It is composed primarily of SINEs that are never transcribed.

33. Regarding the structural organization of human genes, which protein-coding gene is noted for having a completely absent intron structure?

Ovalbumin gene
Titin gene
Hemoglobin β subunit
Histone genes

34. In the human genome, what is the significance of the 28.5% portion categorized as ‘Introns and noncoding segments’?

It represents sequences within genes that are removed during mRNA processing or do not code for protein.
It consists entirely of functional RNA molecules like rRNA and tRNA.
It is synonymous with the 45% of the genome made of transposons.
It is the only part of the genome that contains regulatory DNA sequences.

35. True or False: Most genes that code for RNA as their final product (like rRNA and tRNA) do not contain introns.

False
True

36. Based on the Vital Statistics of the Human Genome, what is the approximate mean gene size and what does this imply when compared to the mean exon size?

Mean gene size is 27,000 bp; since mean exon size is 145 bp, most of the gene consists of introns.
Mean gene size is 2.4×10^6 bp; this suggests that exons are typically thousands of base pairs long.
Mean gene size is 1,500 bp; this indicates that human genes are very compact like those in yeast.
Mean gene size is 17,106 bp; this represents the length of the protein-coding sequence.

37. The Indian Muntjac and Chinese Muntjac have vastly different chromosome numbers despite being closely related. What does this illustrate?

The Indian Muntjac has no Y chromosome, unlike the Chinese Muntjac.
Species with few chromosomes lack the 'junk DNA' found in species with many chromosomes.
The number of chromosomes can vary considerably between eukaryotic organisms without necessarily changing gene content.
Organisms with more chromosomes are always more biologically complex.

38. What is the approximate size of a LINE (Long Interspersed Element) in the human genome?

6-8 kb
5-10 bp
9-10 kb
100-300 bp

39. Which category of repetitive DNA elements accounts for the largest percentage of the human genome?

Simple Sequence Repeats (SSR)
Introns
Transposons
LINEs (Long Interspersed Elements)

40. Which of the following describes the correct timeline and scope for the Human Genome Project?

Finished in 2001, allowing the ENCODE project to map all genes by 2007.
Started in 1996, draft in 2001, and finished sequence in 2003.
Started in 2003, with the ENCODE project finishing the final draft in 2012.
Started in 1996, with the first 69 individual genomes finished by 2003.

41. How has the traditional definition of a gene evolved based on recent findings in the human genome?

It is now restricted only to sequences that can be translated into a folded protein structure.
It now includes DNA segments that produce functional RNA molecules without being translated into proteins.
It identifies genes as any sequence of DNA that is biochemically active, regardless of transcription.
It defines a gene solely as a unit of heredity that resides on a centromere.

42. The ENCODE project utilized ChIP-seq primarily to detect which of the following?

The presence of SINEs and LINEs in the E. coli genome.
The rate of telomere shortening in aging cells.
Histone modifications and protein-DNA binding sites.
The exact number of pseudogenes in a family quartet.

43. What is the function of the specific DNA sequences known as centromeres during cell division?

They serve as binding sites for proteins that attach the chromosome to the mitotic spindle.
They protect the ends of the chromosomes from being degraded or shortened.
They contain the instructions for synthesizing histone proteins.
They provide a starting point for DNA replication to begin.

44. What proportion of the human genome is actually transcribed into RNA, even if it does not code for protein?

Less than 10%
Exactly 80%
Approximately 60%
Approximately 30%

45. Which of the following best describes the correlation between the total number of genes and the perceived complexity of an organism?

Complexity is defined strictly by the gene density per 1000 base pairs.
The amount of total DNA (bp) is the only accurate predictor of an organism's complexity.
There is only some correlation, as some plants like rice have significantly more genes than humans.
There is a linear correlation where higher chromosome numbers always result in higher gene counts.

46. Which portion of the human genome is described as ‘Miscellaneous’ and includes simple sequence repeats (SSR) and segmental duplications (SD)?

45%
80%
1.5%
25%

47. According to the ENCODE project, what percentage of the human genome is estimated to be involved in the regulation of gene expression?

Approximately 20%
Approximately 60%
Approximately 45%
Exactly 1.5%

48. How do the SINEs and LINEs differ in terms of their physical size within the genome?

LINEs consist of short repeats of 5−10 bp, while SINEs are 6−8 kb.
SINEs are thousands of base pairs long, whereas LINEs are only a few hundred.
LINEs are 6−8 kb in length, whereas SINEs are 100−300 bp.
Both SINEs and LINEs are typically 9−10 kb in length.

49. In the human genome, what percentage of the total sequence is actually comprised of exons (protein-coding sequences)?

28.5%
1.5%
30%
45%

50. What is the mean gene size in the human genome?

145 nucleotide pairs
3,000 nucleotide pairs
2.4×10^6 nucleotide pairs
27,000 nucleotide pairs

51. In the case study of the family quartet, which finding demonstrates the predictive power of whole-genome sequencing regarding pharmacogenomics?

The prediction of obesity for the daughter and son.
The confirmation that the mother already displayed clinical symptoms of psoriasis.
The identification of a novel synthetic human reference sequence based on the daughter's DNA.
The determination of the accurate dose of blood thinners for the father.

52. What was a major implication of the 2012 ENCODE project regarding non-coding RNA?

They proved that non-coding RNAs have no biochemical function in the cell.
They found that non-coding RNAs are only present in yeast and bacteria.
They identified approximately 8,800 small RNA molecules and 9,600 long noncoding RNAs.
They discovered that non-coding RNA makes up 45% of the genome.