Viral genetics

Question 1

Are most viruses haploid or diploid?

Answer 1

Most are haploid (one copy of genetic material)

Question 2

All viruses are haploid except ___

Answer 2

Retroviruses (2 copies of single-stranded RNA)

Question 3

Genetic principles in virology

Answer 3

• Recombination
• Reassortment
• Complementation
• Phenotypic mixing

Question 4

Genetic principle behind H1N1 influenza epidemic

Answer 4

Reassortment; when viruses with segmented genomes (eg, influenza virus) exchange genetic material

Question 5

Why is Hepa B required for Hepa D infection? What genetic principle applies?

Answer 5

• Hepatitis D virus requires the presence of replicating hepatitis B virus to supply HBsAg, the envelope protein for HDV
• Complementation
  
  • When 1 of 2 viruses that infect the cell has a mutation that results in a nonfunctional protein, the non-mutated virus “complements” the mutated one by making a functional protein that serves both viruses

Question 6

Exchange of genes between 2 chromosomes by crossing over within regions of significant base sequence homology

Answer 6

Recombination

Memory aid:

• Re_C_ombination
• _C_hromosomes
• _C_ross over

Question 7

When viruses with segmented genomes (eg, influenza virus) exchange genetic material

Answer 7

Reassortment

Memory aid:

• Rea_S_sortment
• _S_egmented

Question 8

Examples of segmented viruses

Answer 8

• Bunyaviruses
• Orthomyxoviruses (influenza viruses)
• Arenaviruses
• Reoviruses

Question 9

Sequela (e) in influenza virus if reassortment happens

Answer 9

Can cause genetic shift/antigenic shift

Question 10

When 1 of 2 viruses that infect the cell has a mutation that results in a nonfunctional protein, the non-mutated virus “complements” the mutated one by making a functional protein that serves both viruses

Answer 10

Complementation

Question 11

Example of complementation

Answer 11

Hep D and B

Question 12

Occurs with simultaneous infection of a cell with 2 viruses

Answer 12

Definition

Note:

• Phenotype mixing occurs when the genome of virus A is coated with the surface proteins of virus B and infectivity is determined by the virus B protein coat, but the progeny is encoded by virus A genetic material and will have the virus A coat

Question 13

Which type of viral genetic event can cause worldwide pandemics?

Answer 13

Reassortment, which happens when viruses with segmented genomes (eg, influenza virus) exchange segments

Question 14

Viral genome reassortment occurs in viruses with what type of genomic structure?

Answer 14

Segmented genomes