Microbiology & Biotechnology

Microbiology & Biotechnology

Multiple genes are involved in the inheritance of which of the following disease:

Skin color exhibits polygenic inheritance controlled by multiple loci such as MC1R, SLC24A5, TYR producing continuous variation. In contrast, color blindness, sickle-cell anemia, and phenylketonuria follow monogenic Mendelian patterns, not requiring cumulative additive effects of several independent genes.

Ref: Hartl, Principles of Population Genetics, 4th Edition, Chapter 8, Quantitative and Polygenic Inheritance, explains skin color as polygenic trait controlled by multiple genes with additive effects versus monogenic disorders like sickle-cell and phenylketonuria, published by Sinauer Associates.

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Microbiology & Biotechnology

Person having sex chromosomes XXY suffers from which of the following:

Klinefelter syndrome karyotype 47,XXY results from nondisjunction causing extra X chromosome in males, presenting tall stature, small testes, gynecomastia, and infertility. It contrasts with Down trisomy 21, Edwards trisomy 18, and Patau trisomy 13 autosomal aneuploidies.

Ref: Thompson and Thompson, Genetics in Medicine, 8th Edition, Chapter 6, Human Chromosome Aneuploidies, discusses Klinefelter syndrome 47 XXY karyotype due to nondisjunction, clinical features and comparison with Down and Edwards syndromes, published by Elsevier Saunders.

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Microbiology & Biotechnology

Crossing over occurs in which phase:

Homologous recombination via crossing over occurs during pachytene stage of prophase I in meiosis, mediated by synaptonemal complex and recombination nodules exchanging chromatid segments. This generates genetic variation and ensures proper segregation, absent in telophase, anaphase, and metaphase I.

Ref: Hartl and Jones, Genetics: Analysis of Genes and Genomes, 8th Edition, Chapter 3, Meiosis and Crossing Over, details pachytene stage of prophase I, synaptonemal complex formation and homologous recombination generating genetic diversity, published by Jones and Bartlett Learning.

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Microbiology & Biotechnology

The original codon changes to stop codon in which type of mutation:

Nonsense mutation substitutes a coding codon with UAA, UAG, or UGA termination codon, causing premature translation stop and truncated nonfunctional protein. It differs from missense which alters amino acid identity and sense mutation retaining coding meaning, often leading to loss-of-function.

Ref: Griffiths et al., Introduction to Genetic Analysis, 11th Edition, Chapter 10, Types of Mutations, defines nonsense mutation creating premature UAA, UAG, UGA stop codons causing truncated proteins versus missense and sense mutations, published by W H Freeman.

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Microbiology & Biotechnology

Human telomeres consist of tandem repeats if sequence:

Human telomeres consist of conserved TTAGGG tandem repeats synthesized by telomerase to prevent chromosome end attrition. This G-rich hexanucleotide forms t-loop and G-quadruplex structures protecting genome stability, unlike variant sequences not found in vertebrate telomeres.

Ref: Alberts et al., Molecular Biology of the Cell, 6th Edition, Chapter 5, Telomeres and Telomerase, describes human telomeric repeat sequence TTAGGG tandem arrays, t-loop formation and maintenance by telomerase enzyme, published by Garland Science.

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Microbiology & Biotechnology

If the amount of ‘G’ in a DNA sample is 20%. What will be the amount of ‘T’?

According to Chargaff's rule in double-stranded DNA, G pairs with C and A pairs with T. If G is 20%, C is 20%, leaving 60% for A+T, so T equals 30%. This parity reflects base complementarity and antiparallel duplex stability.

Ref: Watson et al., Molecular Biology of the Gene, 7th Edition, Chapter 6, DNA Structure and Chargaff Rules, explains base pairing parity where amount of guanine equals cytosine and calculated thymine proportion from guanine percentage, published by Pearson Education.

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Microbiology & Biotechnology

Which of the following amino acid is present abundantly in histones?

Histones are highly basic proteins enriched in arginine and lysine residues, whose positively charged guanidinium groups electrostatically bind acidic phosphate backbone of DNA. This abundance enables tight nucleosome compaction, chromatin organization, and regulation of gene accessibility during transcription.

Ref: Nelson and Cox, Lehninger Principles of Biochemistry, 7th Edition, Chapter 28, Chromatin Structure and Histones, discusses basic amino acid enrichment of arginine and lysine in histones for electrostatic interaction with DNA phosphate backbone, published by W H Freeman.

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Microbiology & Biotechnology

Which of the following takes place in both bacterial as well as eukaryotic mRNA synthesis?

Both prokaryotes and eukaryotes synthesize mRNA through DNA-dependent RNA polymerase transcribing complementary RNA from template strand. Capping, poly-A tailing, and spliceosome-mediated splicing are eukaryote-specific post-transcriptional modifications absent in bacteria, which couple transcription and translation.

Ref: Lewin, Genes XI, 11th Edition, Chapter 12, Transcription and RNA Polymerases, describes DNA-dependent RNA synthesis as universal step in both bacterial and eukaryotic mRNA formation, distinguishing capping and polyadenylation, published by Jones and Bartlett Learning.

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Microbiology & Biotechnology

Which of the following vector contains telomeric sequences?

Yeast artificial chromosomes contain autonomous replication sequences, centromere, selectable markers, and telomeric repeats to replicate stably as linear chromosomes in yeast. Plasmid, lambda, and M13 vectors lack telomeres, as bacteria and phages maintain circular genomes without telomeric structures.

Ref: Primrose and Twyman, Principles of Gene Manipulation and Genomics, 8th Edition, Chapter 5, Cloning Vectors for Eukaryotes, explains yeast artificial chromosomes containing telomeres, centromeres and autonomously replicating sequences for stable maintenance, published by Wiley Blackwell.

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Microbiology & Biotechnology

The uptake of external DNA into bacterial cell is facilitated in the presence of

Calcium chloride renders E. coli competent by neutralizing negative charges on DNA phosphate backbone and membrane phospholipids, increasing membrane permeability and facilitating DNA adsorption. Heat shock then promotes uptake, a method widely used for plasmid transformation in molecular cloning laboratories.

Ref: Brown, Gene Cloning and DNA Analysis, 7th Edition, Chapter 2, Transformation and Competent Cells, details calcium chloride mediated artificial competence, membrane destabilization and plasmid uptake in Escherichia coli, published by Wiley Blackwell.

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Microbiology & Biotechnology

In gel electrophoresis, which of the following molecule will move faster if the amount of DNA present is same in all?

Supercoiled plasmid DNA is most compact conformation with reduced hydrodynamic radius and greater charge density, migrating fastest through agarose matrix under electric field. Nicked open-circular form is bulkiest and slowest, while linear migrates intermediate when identical mass loads.

Ref: Sambrook and Russell, Molecular Cloning: A Laboratory Manual, 3rd Edition, Volume 1, Chapter 5, describes agarose gel electrophoresis migration of supercoiled, linear and nicked plasmid isoforms based on conformation and compactness, published by Cold Spring Harbor Laboratory Press.

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Microbiology & Biotechnology

The TATA box:

TATA box, AT-rich consensus sequence around -25 to -30 upstream of transcription start, located on non-template coding strand, binds TBP of TFIID to position RNA polymerase II pre-initiation complex, facilitating basal transcription, not silencing gene expression.

Ref: Lodish et al., Molecular Cell Biology, 8th Edition, Chapter 8, Eukaryotic Transcription Initiation, explains TATA box consensus at -25 position, TBP binding and recruitment of RNA polymerase II pre-initiation complex, published by W H Freeman.

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