Molecular Biology and Genomics Practice Questions

Q: In which of the following conditions is a Barr body absent in females?

45 X0 genome. ***45 X0 genome*** - A Barr body is a **condensed, inactivated X chromosome** found in somatic cells of females with at least two X chromosomes. - Individuals with a **45 X0 genome** (Turner Syndrome) have only one X chromosome, therefore no Barr body is formed. *46 XX genome* - Individuals with a **46 XX genome** are typical females and will have one Barr body per somatic cell, as one of the two X chromosomes is inactivated. - This is the normal female karyotype. *47 XXX* - Individuals with a **47 XXX genome** (triple X syndrome) have two Barr bodies per somatic cell, as two of their three X chromosomes are inactivated. - The number of Barr bodies is typically one less than the number of X chromosomes. *None of the options* - This option is incorrect because the 45 X0 genome indeed leads to the absence of a Barr body in females. - There is a specific condition listed among the options where a Barr body is absent.

Q: Effect of environment on genes is called?

Epigenetics. ***Epigenetics*** - **Epigenetics** refers to heritable changes in **gene expression** that do not involve alterations to the underlying **DNA sequence**. - These changes are often influenced by **environmental factors**, such as diet, stress, and exposure to toxins, which can affect how genes are turned on or off. *Positive Eugenics* - **Positive eugenics** aims to improve the human population by encouraging the reproduction of individuals deemed to have "desirable" traits. - This concept is ethically controversial and focuses on directed breeding rather than environmental gene influence. *Negative Eugenics* - **Negative eugenics** aims to reduce the prevalence of "undesirable" traits in the human population by discouraging or preventing the reproduction of individuals deemed to possess them. - Like positive eugenics, this is a highly controversial concept focused on limiting reproduction based on perceived genetic quality. *Euthenics* - **Euthenics** is a movement focused on improving human well-being and development by improving living conditions and the environment. - While it acknowledges the impact of the environment, it focuses on societal and lifestyle improvements rather than the direct molecular changes in gene expression.

Q: Who invented the technique for identifying individuals by their DNA?

Jeffreys. ***Jeffreys*** - **Alec Jeffreys** developed the technique of **DNA fingerprinting** in 1984, which revolutionized forensic science and paternity testing. - His method involved analyzing **variable number tandem repeats (VNTRs)** in DNA to create a unique profile for each individual. *Shapiro* - **Robert Shapiro** is a legal figure, famously associated with the O. J. Simpson murder trial, not directly with the invention of DNA identification techniques. - While he was involved in cases where DNA evidence was used, he did not contribute to its scientific development. *Lewis* - **Edward B. Lewis** was a Nobel Prize-winning geneticist known for his work on **developmental genetics** in *Drosophila melanogaster*, not for DNA identification techniques. - His research focused on gene clusters and their role in embryonic development. *Pasteur* - **Louis Pasteur** was a pioneering microbiologist and chemist, famous for his discoveries related to **vaccination**, microbial fermentation, and pasteurization. - His work predates the discovery and application of DNA for individual identification by over a century.

Q: What is the primary function of reverse transcription?

Synthesis of DNA from an RNA template. ***Synthesis of DNA from an RNA template*** - **Reverse transcription** is catalyzed by the enzyme **reverse transcriptase**, which uses an **RNA template** to synthesize a complementary DNA (cDNA) strand. - This process is fundamental in the life cycle of **retroviruses** like HIV, allowing them to integrate their genetic material into the host genome. *Synthesis of RNA from a DNA template* - This process is known as **transcription**, where genetic information is copied from **DNA to RNA**, not the reverse. - It is a key step in gene expression, leading to the production of various types of RNA molecules. *Synthesis of DNA from a DNA template* - This describes **DNA replication**, the process by which DNA makes copies of itself, ensuring genetic continuity during cell division. - It involves enzymes like **DNA polymerase** and creates two identical DNA molecules from one original DNA molecule. *Synthesis of RNA from an RNA template* - This process is known as **RNA replication** and is characteristic of certain **RNA viruses** (e.g., influenza virus), where RNA serves as both the template and the genetic material. - It involves an enzyme called **RNA-dependent RNA polymerase**.

Q: In which stage of cell division is chromosomal study best carried out?

Metaphase. ***Metaphase*** - During **metaphase**, chromosomes are maximally condensed and align at the cell's equatorial plate, making them easily visible and distinguishable under a microscope. - This arrangement allows for clear visualization of **chromosome number**, **size**, and **morphology**, which is crucial for genetic analysis. *Prophase* - In **prophase**, chromosomes begin to condense, but they are still diffuse and not fully compact, making detailed study difficult. - The nuclear envelope is also still present for most of prophase, obstructing a clear view of the chromosomes. *Telophase* - During **telophase**, chromosomes decondense and arrive at opposite poles, becoming less distinct and harder to analyze individually. - New nuclear envelopes form around the separated chromosomes, further obscuring their view for detailed study. *Anaphase* - In **anaphase**, sister chromatids separate and move towards opposite poles, but they are in motion and not aligned, making them difficult to capture and analyze individually. - The separated chromatids are also stretched and elongated, which makes their morphological assessment challenging.

Q: Which of the following statements is most specifically characteristic of mature cytoplasmic messenger RNA (mRNA) compared to its precursor?

Has a lower molecular weight than hn-RNA.. ***Has a lower molecular weight than hn-RNA.*** - **Mature mRNA** undergoes **splicing**, which removes **introns** (non-coding regions) from the heterogeneous nuclear RNA (hnRNA) precursor. - The removal of these introns results in a **shorter, more compact molecule** with a lower molecular weight compared to the original hnRNA. *Transcribed from nuclear DNA.* - While mRNA is indeed **transcribed from DNA**, this statement is true for **all types of RNA (rRNA, tRNA, and mRNA)**, not just mature cytoplasmic mRNA specifically, and does not differentiate it. - The initial transcript is **hnRNA**, which is then processed into mature mRNA. *Contains uracil instead of thymine.* - This is a characteristic of **all RNA molecules**, not just mature cytoplasmic mRNA, and is a fundamental difference between RNA and DNA. - DNA contains **thymine**, while RNA contains **uracil**. *Sugar is ribose.* - This is a distinguishing feature of **all RNA molecules**, indicating that the sugar component of its nucleotides is **ribose**, whereas DNA contains **deoxyribose**. - This statement is not unique to mature cytoplasmic mRNA.

Q: DNA microarrays allow detection of gene mutations through which process?

Hybridization. ***Hybridization*** - DNA microarrays detect mutations by **hybridizing labeled patient DNA** to **thousands of oligonucleotide probes** containing known DNA sequences immobilized on a solid surface. - A mismatch between the patient's DNA and the probe results in **reduced or absent hybridization**, indicating a **mutation or genetic variation**. - This principle allows **high-throughput screening** of multiple genes simultaneously. *Polymerase Chain Reaction* - PCR is used to **amplify specific DNA sequences exponentially**, creating millions of copies from minimal starting material. - While PCR may be used to **prepare DNA samples** before microarray analysis, it is **not the detection mechanism** on the chip itself. *Cloning* - Cloning involves creating **identical copies of DNA fragments, cells, or organisms** using vectors and host cells. - It's a method for **producing large quantities** of specific DNA sequences but **not a detection technique** for mutations on microarrays. *Southern Blotting* - Southern blotting detects specific DNA sequences through **gel electrophoresis, membrane transfer, and probe hybridization**. - While it also uses hybridization, it is a **low-throughput technique** analyzing one sample at a time, unlike the **high-throughput parallel analysis** of DNA microarrays.

Q: The Central Dogma of molecular biology includes all except?

Reverse transcription. ***Reverse transcription*** - The **original Central Dogma** as proposed by Francis Crick described the unidirectional flow of genetic information: **DNA → RNA → Protein**. - **Reverse transcription** (RNA → DNA) was **not part of the original Central Dogma** and was only discovered later with the identification of **reverse transcriptase enzyme** in retroviruses by Baltimore and Temin (1970). - While reverse transcription is now recognized as an important biological process, it represents an **exception to the classical Central Dogma** rather than a core component. *Transcription* - **Transcription** (DNA → RNA) is a **fundamental process** within the Central Dogma. - It involves synthesis of RNA from a DNA template and is the first step in gene expression in all living organisms. *Translation* - **Translation** (RNA → Protein) is the **second major step** of the Central Dogma. - This process occurs on ribosomes where mRNA is decoded into a specific sequence of amino acids to form proteins. *RNA replication* - **RNA replication** (RNA → RNA), while primarily seen in RNA viruses, is considered part of the **expanded Central Dogma**. - It represents one of the possible flows of genetic information in biological systems, though not universal to all organisms.

Q: What is the classification of the Y chromosome?

Submetacentric. ***Submetacentric*** - The **Y chromosome** is classified as submetacentric because its **centromere** is located off-center, resulting in two arms of unequal length. - The short arm (Yp) is smaller than the long arm (Yq), but not as disproportionate as in acrocentric chromosomes. - The **X chromosome** is also submetacentric, making both sex chromosomes belong to this category. *Metacentric* - A **metacentric chromosome** has its **centromere** located in the middle, resulting in two arms of approximately equal length. - Examples include chromosomes 1, 3, 16, 19, and 20, which have nearly equal arm ratios unlike the Y chromosome. *Acrocentric* - An **acrocentric chromosome** has its **centromere** located very close to one end, creating one very short arm and one very long arm. - The five acrocentric human chromosomes are **13, 14, 15, 21, and 22**, which possess satellite DNA and nucleolar organizing regions (NORs) on their short arms. - The **Y chromosome is NOT acrocentric** despite historical confusion; it has a more centrally positioned centromere than true acrocentric chromosomes. *None of the options* - This option is incorrect because the Y chromosome has a specific and well-established classification as **submetacentric** based on its centromere position and arm ratio.

Q: Function of reverse transcriptase is

RNA dependent DNA synthesis. ***RNA dependent DNA synthesis*** - **Reverse transcriptase** is an enzyme that catalyzes the formation of **DNA from an RNA template**, a process known as reverse transcription. - This function is crucial for **retroviruses** like HIV, which use it to integrate their RNA genome into the host cell's DNA. *DNA dependent RNA synthesis* - This process is known as **transcription**, carried out by **RNA polymerase**. - It involves the synthesis of **RNA from a DNA template**, the opposite of reverse transcription. *DNA dependent DNA synthesis* - This process is known as **DNA replication**, carried out by **DNA polymerase**. - It involves the synthesis of **new DNA strands from existing DNA templates**. *RNA dependent RNA synthesis* - This process is characteristic of **RNA viruses**, specifically those with **RNA replicase** enzymes. - These enzymes synthesize **new RNA strands from an RNA template** for viral replication.

Question 1

In which of the following conditions is a Barr body absent in females?

Accepted Answer

45 X0 genome

Answer

46 XX genome

Answer

47 XXX

Answer

None of the options

Question 2

Effect of environment on genes is called?

Accepted Answer

Epigenetics

Answer

Euthenics

Answer

Positive Eugenics

Answer

Negative Eugenics

Question 3

Who invented the technique for identifying individuals by their DNA?

Accepted Answer

Jeffreys

Answer

Shapiro

Answer

Lewis

Answer

Pasteur

Question 4

What is the primary function of reverse transcription?

Accepted Answer

Synthesis of DNA from an RNA template

Answer

Synthesis of RNA from a DNA template

Answer

Synthesis of DNA from a DNA template

Answer

Synthesis of RNA from an RNA template

Question 5

In which stage of cell division is chromosomal study best carried out?

Accepted Answer

Metaphase

Answer

Telophase

Answer

Anaphase

Answer

Prophase

Question 6

Which of the following statements is most specifically characteristic of mature cytoplasmic messenger RNA (mRNA) compared to its precursor?

Accepted Answer

Has a lower molecular weight than hn-RNA.

Answer

Transcribed from nuclear DNA.

Answer

Contains uracil instead of thymine.

Answer

Sugar is ribose.

Question 7

DNA microarrays allow detection of gene mutations through which process?

Accepted Answer

Hybridization

Answer

Polymerase Chain Reaction

Answer

Cloning

Answer

Southern Blotting

Question 8

The Central Dogma of molecular biology includes all except?

Accepted Answer

Reverse transcription

Answer

Transcription

Answer

RNA replication

Answer

Translation

Question 9

What is the classification of the Y chromosome?

Accepted Answer

Submetacentric

Answer

Metacentric

Answer

Acrocentric

Answer

None of the options

Question 10

Function of reverse transcriptase is

Accepted Answer

RNA dependent DNA synthesis

Answer

DNA dependent RNA synthesis

Answer

DNA dependent DNA synthesis

Answer

RNA dependent RNA synthesis

Molecular Biology and Genomics — MCQs

Molecular Biology and Genomics — MCQs

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