Molecular Biology and Genomics Practice Questions

Q: Which of the following statements about mitochondrial gene inheritance is true?

Mitochondrial genes are inherited from the mother.. ***Mitochondrial genes are inherited from the mother.*** - During fertilization, the **ovum** contributes the vast majority of the cytoplasm, including all the mitochondria, to the zygote. - This results in a distinctive pattern of **maternal inheritance** for mitochondrial DNA (mtDNA); only mothers pass mitochondria to all their offspring. *Mitochondrial gene mutations are inherited in a paternal pattern.* - This statement is incorrect because mitochondrial inheritance is exclusively **maternal**, meaning mutations are passed from the mother, not the father. - Paternal DNA is primarily contained within the nucleus of the sperm head, and very few, if any, paternal mitochondria enter the oocyte during fertilization. *Mitochondrial genes are inherited from the father.* - This is incorrect as mitochondria are almost exclusively inherited from the **mother's ovum**. - The sperm provides its nuclear DNA but typically contributes negligible or no mitochondria to the zygote. *Mitochondrial genes follow Mendelian inheritance.* - Mitochondrial inheritance is **non-Mendelian**; it does not follow the classic dominant/recessive patterns or segregation expected with nuclear genes. - Due to maternal inheritance, all offspring of an affected mother will inherit the mitochondrial condition, regardless of sex.

Q: BRCA1 gene is located on which chromosome?

17q21. ***17q21*** - The **BRCA1 gene** is located on the long arm (q) of **chromosome 17** at region 21. - This gene plays a crucial role in **DNA repair** and is associated with an increased risk of breast and ovarian cancers. *13q12* - This location corresponds to the **BRCA2 gene**, which is also involved in DNA repair and cancer predisposition. - While both BRCA1 and BRCA2 are significant, they are distinct genes on different chromosomes. *12q13* - This is not the correct chromosomal location for either BRCA1 or BRCA2. - Various other genes are located on chromosome 12, but not BRCA1. *21q17* - This is an incorrect chromosomal designation; the "q" arm designation is typically followed by a band number, and 17 is not a standard band number for chromosome 21 in this context. - **Chromosome 21** is primarily associated with **Down syndrome** (trisomy 21).

Q: Which of the following is not a method for introducing a gene into target cells?

FISH. ***FISH*** - **FISH (Fluorescence In Situ Hybridization)** is a cytogenetic technique used to detect and localize the presence or absence of specific **DNA sequences** on chromosomes. - It is an imaging and diagnostic technique, not a method for introducing genetic material into cells. *Electroporation* - **Electroporation** is a physical method that uses an **electric pulse** to create temporary pores in cell membranes. - These temporary pores allow for the direct uptake of **exogenous DNA** (or other molecules) into the cell. *Transfection* - **Transfection** is a general term referring to the process of deliberately introducing **nucleic acids (DNA or RNA)** into eukaryotic cells. - It encompasses various methods, including chemical (e.g., lipid-based), physical (e.g., electroporation), and viral approaches. *Site directed recombination* - **Site-directed recombination** is a molecular biology technique used to introduce **targeted genetic changes** (insertions, deletions, or substitutions) at specific locations in a genome. - This process involves the direct introduction of modified genetic material that then recombines with the host genome.

Q: Which of the following statements is true regarding the role of enzymes in recombinant DNA technology?

DNA ligase is used. ***DNA ligase is used*** - **DNA ligase** plays a crucial role in **recombinant DNA technology** by forming **phosphodiester bonds** to join DNA strands, such as in inserting a gene into a plasmid. - This enzyme is essential for **recombinant DNA formation** by covalently linking compatible sticky or blunt ends of DNA fragments. - DNA ligase catalyzes the final step of **sealing nicks** in the DNA backbone, creating stable recombinant molecules. *Restriction endonucleases are involved* - **Restriction endonucleases** (restriction enzymes) are indeed crucial for **cutting DNA** at specific recognition sites, creating DNA fragments with sticky or blunt ends. - While absolutely essential to the overall process, this statement uses "are involved" which is less specific than "is used" for describing the ligase's direct role in joining fragments. - Both enzymes work sequentially: restriction enzymes cut, then ligase joins. *Acid phosphatase is used* - **Acid phosphatase** is an enzyme found in lysosomes and is involved in **phosphate group removal** from substrates. - It is not used in **recombinant DNA technology** for cutting or joining DNA fragments. *Reverse transcriptase needed* - **Reverse transcriptase** is used to synthesize **cDNA from an mRNA template**, a process known as reverse transcription. - This enzyme is essential for creating **cDNA libraries** but is not directly involved in the core steps of cutting and joining DNA fragments in standard recombinant DNA procedures.

Q: Transition from G2 to M phase of the cell cycle is controlled by which?

Cyclin B. ***Cyclin B*** - The transition from G2 to M phase is primarily controlled by the **maturation-promoting factor (MPF)**, which is a complex of **cyclin B** and **CDK1 (cyclin-dependent kinase 1)**. - **Cyclin B** levels rise during G2 and peak at M phase, activating CDK1 to initiate mitosis. *Retinoblastoma gene product* - The **retinoblastoma (Rb) protein** primarily regulates the G1/S transition by inhibiting the E2F transcription factor. - It acts as a **tumor suppressor**, preventing uncontrolled cell proliferation. *p53 protein* - The **p53 protein** is a critical **tumor suppressor** that monitors DNA integrity at various cell cycle checkpoints, particularly G1/S and G2/M. - If DNA damage is detected, p53 can induce cell cycle arrest and/or apoptosis, but it is not directly responsible for initiating M phase. *Cyclin E* - **Cyclin E** is essential for the **G1/S transition**, forming a complex with CDK2 to initiate DNA replication. - Its activity peaks during late G1 and early S phase, not during the G2/M transition.

Q: Gene amplification is achieved through

Polymerase Chain Reaction. ***Polymerase Chain Reaction*** - **PCR** is the **gold standard** molecular biology technique that generates **millions to billions of copies** of a specific DNA segment over a short period. - It utilizes a cyclical process of **denaturation**, **annealing**, and **extension** with **thermostable DNA polymerase** to achieve exponential amplification. - **Most widely used** method for gene amplification in research and diagnostics. *DNA strand hybridization* - **DNA strand hybridization** is the process where two complementary single-stranded DNA molecules bind together to form a **double-stranded molecule**. - This process is fundamental to many molecular techniques but does not, in itself, achieve **amplification**; rather, it is a **binding event**. *In situ DNA hybridization* - **In situ hybridization** is a technique that localizes and detects specific **nucleic acid sequences** (DNA or RNA) within cells or tissues directly on a slide. - While it uses **hybridization**, its primary purpose is **detection and localization**, not the **amplification** of DNA sequences. *Ligase chain reaction (LCR)* - **LCR** is a molecular technique that does amplify DNA sequences exponentially using **DNA ligase** to join adjacent oligonucleotide probes. - However, it is **less commonly used** than PCR, has more **stringent requirements** (requires knowledge of both strands), and is primarily used for detecting **known point mutations** rather than general gene amplification. - **PCR remains the standard** technique when the question refers to gene amplification without additional qualifiers.

Q: Which of the following is the origin of the mitochondrial DNA of all human adult cells?

Maternal only. ***Maternal only*** - **Mitochondria** and their DNA are almost exclusively inherited from the **mother's ovum**. - During fertilization, the sperm contributes only its nucleus to the zygote, while the ovum provides the bulk of the cytoplasm, including mitochondria. *Paternal only* - The **sperm's mitochondria** are typically found in its tail and are usually **destroyed** or degrade after entering the egg, or are actively excluded. - This prevents paternal mitochondrial DNA from being passed on to the offspring. *A combination of paternal and maternal DNA is inherited* - While nuclear DNA is a combination of paternal and maternal contributions, **mitochondrial DNA** inheritance is **uniparental** (from one parent only). - This is a fundamental aspect of human genetics and ancestry tracking. *Either paternal or maternal DNA is inherited* - This option incorrectly suggests variability, as **maternal inheritance** of mitochondrial DNA is the virtually universal rule in humans. - Rare exceptions of paternal mitochondrial DNA inheritance have been reported but are considered **anomalous** and not typical.

Q: What term describes the external manifestations of the genome?

Phenotype. ***Correct: Phenotype*** - The **phenotype** refers to the **observable characteristics** or traits of an organism, which result from the interaction of its genotype with the environment. - These external manifestations can include physical appearances (e.g., eye color), physiological traits (e.g., blood pressure), and even measurable behaviors. - This is the classic definition of phenotype - the external/outward expression of the genome. *Incorrect: Genotype* - The **genotype** describes the **genetic makeup** of an individual, specifically the set of alleles possessed for a particular gene or genes. - It represents the internal genetic code, not its outward expression. - Genotype is the "blueprint," while phenotype is the "building." *Incorrect: Allele* - An **allele** is one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome. - It is a specific variation of a gene, not the observable manifestation of the entire genome. - Alleles are components of the genotype. *Incorrect: Polymorphism* - A **polymorphism** is a common variation in the DNA sequence among individuals in a population. - It refers to differences in the genetic code itself, not the resulting physical or functional traits. - Polymorphisms contribute to genetic diversity at the DNA level.

Q: Xeroderma pigmentosum is due to:

Nucleotide excision defect. ***Nucleotide excision defect*** - **Xeroderma pigmentosum (XP)** is a genetic disorder characterized by a defect in the **nucleotide excision repair (NER)** pathway. - This pathway is crucial for repairing **DNA damage**, particularly **pyrimidine dimers** caused by **ultraviolet (UV) radiation**. *Base excision repair defect* - **Base excision repair (BER)** is a distinct DNA repair pathway that primarily deals with **small, non-helix-distorting base lesions** and single-strand breaks. - Defects in BER are associated with different conditions, such as some forms of **cancer susceptibility** but not XP. *Cross-linking repair defect* - **Cross-linking repair** mechanisms address formations where two strands of DNA are covalently linked, or DNA is linked to proteins, often by agents like **alkylating agents**. - Disorders like **Fanconi anemia** are associated with defects in **DNA interstrand crosslink repair**, which is different from the UV-induced damage seen in XP. *SOS repair mechanism defect* - The **SOS response** is a global bacterial mechanism dealing with extensive DNA damage, primarily involving the induction of various DNA repair enzymes. - There isn't a direct human disease called "SOS repair mechanism defect" that is analogous to XP; human repair mechanisms are more complex and distinct from the bacterial SOS response.

Question 1

Which of the following statements about mitochondrial gene inheritance is true?

Accepted Answer

Mitochondrial genes are inherited from the mother.

Answer

Mitochondrial gene mutations are inherited in a paternal pattern.

Answer

Mitochondrial genes are inherited from the father.

Answer

Mitochondrial genes follow Mendelian inheritance.

Question 2

BRCA1 gene is located on which chromosome?

Accepted Answer

17q21

Answer

13q12

Answer

12q13

Answer

21q17

Question 3

Which of the following is not a method for introducing a gene into target cells?

Accepted Answer

FISH

Answer

Electroporation

Answer

Transfection

Answer

Site directed recombination

Question 4

Which of the following statements is true regarding the role of enzymes in recombinant DNA technology?

Accepted Answer

DNA ligase is used

Answer

Acid phosphatase is used

Answer

Reverse transcriptase needed

Answer

Restriction endonucleases are involved

Question 5

Transition from G2 to M phase of the cell cycle is controlled by which?

Accepted Answer

Cyclin B

Answer

Retinoblastoma gene product

Answer

p53 protein

Answer

Cyclin E

Question 6

Gene amplification is achieved through

Accepted Answer

Polymerase Chain Reaction

Answer

DNA strand hybridization

Answer

In situ DNA hybridization

Answer

Ligase chain reaction (LCR)

Question 7

Which of the following is the origin of the mitochondrial DNA of all human adult cells?

Accepted Answer

Maternal only

Answer

Paternal only

Answer

A combination of paternal and maternal DNA is inherited

Answer

Either paternal or maternal DNA is inherited

Question 8

What term describes the external manifestations of the genome?

Accepted Answer

Phenotype

Answer

Genotype

Answer

Allele

Answer

Polymorphism

Question 9

Xeroderma pigmentosum is due to:

Accepted Answer

Nucleotide excision defect

Answer

Base excision repair defect

Answer

Cross-linking repair defect

Answer

SOS repair mechanism defect

Question 10

Which of the following best defines genomic imprinting?

Accepted Answer

Different expression of a gene depending on the parent of origin.

Answer

Expression of genes silenced on one chromosome through random X-inactivation.

Answer

Parent-specific gene expression due to chromosomal deletions only.

Answer

Uniparental disomy is a condition where both alleles come from one parent.

Molecular Biology and Genomics — MCQs

Molecular Biology and Genomics — MCQs

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