Genetics & Plant Biology

Genetics & Plant Biology

Which of the following enzyme participates in both the citric acid cycle and the electron transport chain?

Succinate dehydrogenase catalyzes oxidation of succinate to fumarate in citric acid cycle while directly transferring electrons to FAD becoming FADH2. It is embedded in inner mitochondrial membrane as Complex II of respiratory chain, linking TCA cycle to electron transport unlike other soluble dehydrogenases.

Ref: Lodish, Berk, Molecular Cell Biology and Bioenergetics, And Stryer Biochemistry, 9th Edition, Chapter 17 Citric Acid Cycle, Cites succinate dehydrogenase oxidizing succinate to fumarate as membrane-bound Complex II participating in both TCA cycle and electron transport chain directly donating electr

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Genetics & Plant Biology

Vitamin B12 deficiency can be diagnosed by urinary excretion of:

Vitamin B12 is cofactor for methylmalonyl-CoA mutase converting L-methylmalonyl-CoA to succinyl-CoA. Deficiency blocks this reaction causing accumulation of methylmalonic acid excreted in urine. Measurement of urinary methylmalonate thus serves as sensitive functional diagnostic marker for cobalamin deficiency distinguishing from folate deficiency.

Ref: Lehninger, Nelson and Cox, Principles of Biochemistry, 8th Edition, Chapter 18 Amino Acid Metabolism and Cofactors, Describes vitamin B12 as cofactor for methylmalonyl-CoA mutase, accumulation and urinary excretion of methylmalonate in deficiency used as diagnostic marker, published by W H Freeman.

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Genetics & Plant Biology

During complete metabolism of glucose, the number of ATP formed is:

Complete aerobic oxidation of one glucose via glycolysis, pyruvate dehydrogenase, citric acid cycle and oxidative phosphorylation yields approximately 30 to 38 ATP depending on shuttle. Traditional textbooks calculate 36 ATP using glycerol-phosphate shuttle accounting, making 36 the classical textbook value taught for glucose metabolism efficiency.

Ref: Berg, Tymoczko, Gatto, Stryer Biochemistry, 9th Edition, Chapter 18 Oxidative Phosphorylation and ATP Yield, Explains complete glucose oxidation through glycolysis, TCA cycle and electron transport yielding approximately 36 ATP per glucose under classical calculation accounting for shuttle systems,

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Genetics & Plant Biology

False about TATA box is that it:

TATA box consensus TATAAA is an AT-rich promoter element located approximately 25 to 35 base pairs upstream of transcription start site, not 10 bp. It binds TBP of TFIID, positioning RNA polymerase II accurately. Pribnow box TATAAT lies at -10 in prokaryotes causing confusion.

Ref: Alberts, Johnson, Lewis, Molecular Biology of the Cell, 6th Edition, Chapter 6 Transcription Control, Details TATA box TATAAA located 25 to 35 base pairs upstream transcription start site binding TBP positioning RNA polymerase II, distinguishes Pribnow -10 box, published by Garland Science.

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Genetics & Plant Biology

If a mutation converts a triplet codon “UGC” to “UGA”, it is called

UGC encodes cysteine while UGA is a termination codon. Mutation changing coding triplet to stop codon prematurely truncates translation, producing nonfunctional polypeptide. Such change introducing premature stop is termed nonsense mutation, distinct from missense altering amino acid or frameshift altering reading frame.

Ref: Lehninger, Nelson and Cox, Principles of Biochemistry, 8th Edition, Chapter 27 Protein Synthesis and Genetic Code, Defines nonsense mutation where codon for amino acid such as UGC cysteine mutates to stop codon UGA terminating translation prematurely, published by W H Freeman.

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Genetics & Plant Biology

In an area where DDT had been used extensively, the population of birds declined significantly because:

DDT biomagnifies and accumulates in avian tissues, disrupting calcium metabolism and inhibiting calcium-ATPase in shell glands. This causes thin, fragile eggshells that crack under incubation, preventing hatching rather than stopping egg production, leading to dramatic population declines in birds like raptors and pelicans.

Ref: Carson, Ecology: From Individuals to Ecosystems Inspired by Begon, Townsend, Harper, 5th Edition, Chapter 12 Pollution Ecology, Explains DDT biomagnification causing eggshell thinning impaired calcium deposition and hatching failure in birds, leading to population decline, published by Wiley-Blackwe

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Genetics & Plant Biology

Bt Cotton is a:

Bt cotton incorporates cry genes from Bacillus thuringiensis encoding insecticidal delta-endotoxin via Agrobacterium-mediated transformation. Expression of Cry1Ac toxin kills lepidopteran bollworm larvae upon ingestion, so Bt cotton contains transgene from bacterium and is classified as transgenic genetically modified plant not conventional hybrid.

Ref: Glick and Patten, Molecular Biotechnology, 5th Edition, Chapter 12 Transgenic Plants, Discusses Bt cotton developed through insertion of Bacillus thuringiensis cry genes encoding insecticidal toxin as classic example of transgenic plant resistant to bollworm, published by ASM Press.

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Genetics & Plant Biology

ABO blood grouping in human beings cites the example of:

ABO locus exhibits three alleles IA, IB, i representing multiple allelism in population. IA and IB are codominantly expressed producing both antigens in AB individuals, while i is recessive. Hence ABO demonstrates both codominance at molecular level and multiple allelism at genetic level.

Ref: Stansfield, Colome, Cano, Molecular and Mendelian Genetics Glossary, And Hartl Genetics Text, 8th Edition, Chapter 2 Blood Groups, Describes ABO system demonstrating both multiple allelism with IA IB i alleles and codominance of IA and IB, published by Jones and Bartlett.

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Genetics & Plant Biology

The expected phenotypic ratio of a dihybrid cross is:

Mendelian dihybrid cross between heterozygotes AaBb x AaBb yields independent assortment of two unlinked genes. Phenotypic classes appear as 9 dominant for both traits, 3 dominant first recessive second, 3 recessive first dominant second, and 1 recessive for both traits overall.

Ref: Snustad and Simmons, Principles of Genetics, 7th Edition, Chapter 3 Mendelian Inheritance Extensions, Details dihybrid cross AaBb x AaBb independent assortment yielding phenotypic ratio 9:3:3:1 representing two character segregation, published by Wiley.

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Genetics & Plant Biology

If a hemophilic man marries a carrier woman, then which of the following holds true for his progenies?

A hemophilic father carries mutant XhY and carrier mother XH Xh. Daughters receive Xh from father and either XH or Xh from mother, yielding 50 percent XH Xh carriers and 50 percent Xh Xh hemophilic daughters. Sons show 50 percent hemophilia as described.

Ref: Hartl, Essential Genetics, 6th Edition, Chapter 4 X-linked Inheritance and Hemophilia, Illustrates cross between hemophilic male XhY and carrier female XH Xh giving 50 percent carrier and 50 percent hemophilic daughters inheritance pattern, published by Jones and Bartlett.

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Genetics & Plant Biology

Restriction endonucleases are very important enzymes used in Genetic engineering. They are used for:

Restriction endonucleases are bacterial enzymes recognizing specific palindromic sequences in double-stranded DNA and cleaving phosphodiester bonds. They generate cohesive or blunt ends for recombinant DNA technology, enabling precise cutting of dsDNA vectors and inserts, while RNA cutting and DNA ligation require distinct enzymes.

Ref: Brown, Genomes, 4th Edition, Chapter 3 Recombinant DNA Technology and Molecular Cloning, Explains restriction endonucleases recognize palindromic double-stranded DNA sequences cleaving phosphodiester bonds generating sticky or blunt ends for genetic engineering, published by Garland Science.

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Genetics & Plant Biology

Which of the following forms left-handed helix?

Z-DNA adopts a left-handed double helix with zigzag phosphate backbone, forming under high salt or alternating purine-pyrimidine GC repeats and negative supercoiling. Unlike right-handed B-DNA and A-DNA and right-handed RNA duplexes, its conformation creates distinct major and minor grooves recognized by proteins.

Ref: Watson, Baker, Bell, Molecular Biology of the Gene, 7th Edition, Chapter 6 Structure of DNA, Describes Z-DNA left-handed helix with zigzag backbone formed by alternating purine-pyrimidine sequences high salt negative supercoiling contrasting right-handed B and A forms, published by Pearson.

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