Viral Genetics

Question 1

What is viral genetics?

Answer 1

It’s the knowledge of mechanism of heritable information in virus.

This heritable information included: Genome structure, replication and genetic changes .

Question 2

What is the reason why virus are continually changing?

Answer 2

Genetic selection

Question 3

What are the two phenomenon in which virus change their genomic structure

Answer 3

Mutation and recombination

Question 4

Phenotypic structure of virus can be changed by?

Answer 4

Interaction between viral grne products.

Question 5

What is mutation?

Answer 5

It’s the change in the DNA sequence of an organism.

This is a result of error during replication.

Question 6

Does mutated virus survive if mutation proved to be lethal?

Answer 6

No they don’t

Question 7

In what condition does mutated virus survive?

Answer 7

I) if it provides selective advantage.
I’m) if it occurs early in the course of infxn

Question 8

What is genetic recombination?

Answer 8

It is the rearrangement of DNA sequences by the breakage and rejoining of chromosomes or chromosome segments.

Question 9

List the four types of genetic recombination:

Answer 9

Intramolecular recombination.
Reassortment
Reactivation
Market rescue/Cross activation.

Question 10

What is reassortment?

Answer 10

This is the exchange of segments between virus to produce various stable virus.

Question 11

Five an example of a virus type that reassortment occur in

Answer 11

Segmented virus

Question 12

Give an example of viruses that undergo reassortment

Answer 12

Arenaviridae
Birnaviridae
Influenza virus A&B
Reoviridae

Question 13

How many segments does Arenavirus have?

Answer 13

2

Question 14

Birnaviridae has how many segments?

Answer 14

2

Question 15

Reoviridae has how many segments?

Answer 15

10-12

Question 16

Buynavirus has how many segments?

Answer 16

3

Question 17

Influenza A and B virus has how many segments?

Answer 17

8

Question 18

Explain the mechanism of Reactivation

Answer 18

. Two virions of the same strain that are lethally mutated in different genes coinfect a host

This results to viable recombinants

Question 19

List the types of virus that undergoe reactivation;

Tips ROP

Answer 19

Poxvirus
Orthomyxovirus
Reovirus.

Question 20

Explain the mechanism of reassortment

Answer 20

An infectious virus and an inactivated virus infects a host simultaneously.

The progeny of infectious virus is produced having active genes from both virus.(Infectious and inactivated)

Question 21

Between what other type of virus can cross reactivation occur?

Answer 21

Infectious & a non infectious virus
Two infectious virus.
Two noninfectious virus.

Question 22

List the three types of interactions between gene Viral products

Answer 22

Complementation
Phenotype mixing
Interference

Question 23

What is complementation

Answer 23

This the interaction of viral gene products in cells infected by two viruses.

Here one or both virus may be defective.

Defective virus: lacks one or more fxnal genes.

If both virus are defective, the fxnal gene of one virus synthesis genetic product (Proteins and enzymes) for the other and vice versa, allowing the growth of both viruses.

If only one is defective, the other stable virus synthesis genetic product that complement the defective virus.

Question 24

Can complementation occur between unrelated viruses?

Answer 24

Yes

Question 25

What is phenotypic mixing

Answer 25

This happens in both enveloped and non enveloped virus.

It is an association of a genotype with a heterologous phenotype.

When two genetically diff virions of same family infect a cell: They can be :

I) Incorporation of the genome of one virus to the capsid protein of another virus -TRANSCAPSIDATION.
This is not a stable genetic change B/c upon replication the phenotypically mixed paren will yield progeny with capsids derived from its genome.

ii) In enveloped virus: PSEUDOTYPE FORMATION.

Virus doesn’t have to closely related.
Nucleocapsid of one virus becomes encased completely with an envelope of another OR

🌻It can be incompletely enveloping with the phenotypically mixed virus having a portion of its normal envelope with antigen and that of the other virus with their antigen.

Question 26

Why is that phenotypic mixing usually occurs btw different members of same virus family?

Answer 26

This is so that the intermixed capsid Proteins must be able to interact with the capsid to form structurally intact capsid.

Question 27

The phenomenon where two viruses simultaneously infect a cell and increases the yield of another is known as?

Answer 27

Enhancement.

Question 28

The phenomenon where two viruses simultaneously infects a host and inhibit the growth of another is known as

Answer 28

Interference.

Question 29

List the 3 mechanism at which interference can occur;

Answer 29

1)Virus A inhibts the ability of Virus B to get absorbed into the cell by blocking or destroying their common receptor.

2) Virus A competing with virus B for its replication components (Polymerase, translation initiation factor)

3) Virus A induces Virus B to produce an inhibitor called Interferon preventing the replication of Virus A