Genetics : Viral Genetics

Study concepts, example questions & explanations for Genetics

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Example Questions

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Example Question #1 : Viral Genetics

When mutating a virus for vaccine development, which of the following characteristics would not be an ideal outcome?

Possible Answers:

altered target cell specificity

reduced pathogenicity

no antigenicity

altered host range

Correct answer:

no antigenicity

Explanation:

A mutated virus for vaccine development must retain antigenicity in order to induce an immune response in the recipient. Reduced pathogenicity, altered host range, or altered target cell specificity would all be desired traits in a vaccine strain.

Example Question #2 : Viral Genetics

Why do RNA viruses have mutation rates higher than those of DNA viruses?

Possible Answers:

RNA viruses are larger

RNA viruses are smaller

RNA viruses lack a proofreading function in the replicatory enzymes.

RNA viruses have a more redundant genetic code

Correct answer:

RNA viruses lack a proofreading function in the replicatory enzymes.

Explanation:

Viral RNA polymerases do not have the same proof-reading ability as DNA polymerases. This is a contributing factor to the difficulty of making vaccines from RNA viruses.  

Example Question #3 : Viral Genetics

Retroviruses are not considered RNA viruses because __________.

Possible Answers:

they are single-stranded

they have a DNA genome

they use DNA intermediates to replicate

they are double-stranded

Correct answer:

they use DNA intermediates to replicate

Explanation:

Retroviruses do have a single-stranded RNA genome, but they use DNA intermediates in replication. Retroviruses utilize reverse transcriptase to convert viral RNA into complementary DNA, which is then copied to produce double-stranded viral DNA.

Example Question #4 : Viral Genetics

Choose the correct answer:

The process by which viruses that have segmented genomes trade segments during replication is known as __________.

Possible Answers:

independent assortment

biosynthesis

mutation

incomplete linkage

Correct answer:

independent assortment

Explanation:

Recombination by independent assortment occurs in viruses that have segmented genomes. Genes are randomly assorted, which can result in the generation of viruses with new antigenic determinants (antigenic shift).

Example Question #5 : Viral Genetics

Retroviruses use __________ to make DNA from their own RNA, before inserting the DNA into the host cell’s genome.

Possible Answers:

reverse transcriptase

membrane fusion

telomerase

endocytosis

retrotransposons

Correct answer:

reverse transcriptase

Explanation:

Reverse transcriptase is an enzyme that can transcribe DNA from RNA, and is used by retroviruses to make a DNA transcript of their own RNA genome. The DNA is then inserted directly into the host’s genome. Endocytosis and membrane fusion are different terms for the process by which viruses insert material into the host cell, but not directly into the genome. Retrotransposons are genetic elements in eukaryotic cells that use reverse transcriptase to duplicate themselves throughout the cell genome. Telomerase is a type of reverse transcriptase found in eukaryotic cells that adds repeated sequences to the ends of chromatids.

Example Question #6 : Viral Genetics

A virus that has not yet entered a host cell contains what type of genetic material?

Possible Answers:

RNA

DNA

Viruses only produce genetic material after entering a host cell.

RNA and DNA

RNA or DNA

Correct answer:

RNA or DNA

Explanation:

Viruses are not universally recognized as living organisms. One of many differences between viruses and other organisms is that all other living organisms contain both DNA and RNA, while viruses only contain one or the other. Some RNA viruses are able to produce DNA using mechanisms such as reverse transcription, but this does not happen until after the virus infects the host cell.

Example Question #7 : Viral Genetics

The process through which segments of different, but similar strains, of viruses in the same cell are combined together to form a new virus is termed what?

Possible Answers:

Genetic drift

Antigenic shift

Conjugation

Transduction 

Antigenic drift

Correct answer:

Antigenic shift

Explanation:

In a cell infected by more than one strain of virus, the segments of the different strains can be combined during viral assembly. Transduction is when DNA is introduced to a cell by a viral vector. Conjugation is when bacteria insert genes into other cells, usually other bacteria, using a pillus. Genetic drift is a term in evolution that applies to all organisms, where allele frequencies in a population change due to random chance. Antigenic drift is when viruses accumulate mutations over time.

Example Question #8 : Viral Genetics

Viruses are classified in part by the type of genetic material they contain. Which of the following is not a classification of viruses?

Possible Answers:

Single-stranded DNA viruses

Double-stranded DNA viruses

Double-stranded RNA viruses

All are classifications of viruses

Single-stranded RNA viruses

Correct answer:

All are classifications of viruses

Explanation:

Viruses have an enormous variety of genome structures, more than any phylum of organism. They have a variety of ways of expressing their genes and replicating, all involving using the host cell’s own machinery.

Example Question #9 : Viral Genetics

Fill in the blanks:

Viruses with __________-fidelity transcriptases have __________ mutation rates.

Possible Answers:

high . . . high

high . . . undetectable

low . . . low

high . . . low

Correct answer:

high . . . low

Explanation:

Viruses that have high-fidelity transcriptases have relatively low mutation rates. Conversely, viruses with low-fidelity transcriptases have relatively high mutation rates. Generally, the higher the fidelity of any enzyme involved in replication of viral nucleic acid, the lower the mutation rate. 

Example Question #10 : Viral Genetics

What part(s) of the virus structure assists in invading host cells?

Possible Answers:

capsid

RNA

DNA

enzyme

spikes

Correct answer:

spikes

Explanation:

Spikes are either composed of hemagglutinin protein (HA) or protein neuraminidase (NA). HA helps the virus link with the host cell membrane while NA allows the release of a newly formed viral particle from the host cell.

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