Antigenic drift is in flu viruses, minor changes in viral proteins due to gene mutation

In flu viruses, antigenic shift is major change in the viral protein due to gene reassortment

A concatemer is two or more identical linear nucleic acid molecules in tandem

A hepadnavirus is a vrisu whose DNA genome replicates by way of an RNA intermediate

A negative strand is a nucleic acid strand that has the opposite snese to the mRNA that is produced

Nucleocapsid is the complete complex of nucleic acid and protein packaged in a virus particle

Overlapping genes are tow or more genes in which part of all of the one gene is embedded in the other

The positive strand is a nucleic acid strand that has the same sense as the mRNA

A polyprotein is a large protein expressed from a single gene and subsequently cleaved to form several individual proteins

A replicative form is a double-stranded DNA moelcule that is an intermediate in the replication of single-stranded DNA viruses

RNA replicase is an enzyme that can produce RNA from an RNA template

Rolling circle replication is a mechanism used by some plasmids and viruses of replicating circular DNA which starts by nicking and unrolling one strand and using the other still circular strand as a template for DNA synthesis

Transposase is an enzyme that catalyzes the insertion of DNA segments into other DNA molecules