The genome is 3020–3320 nucleotides long (for the full length strand) and 1700–2800 nucleotides long (for the short length strand).
The virus is divided into four major serotypes (adr, adw, ayr, ayw) based on antigenic epitopes present on its envelope proteins.
These serotypes are based on a common determinant (a) and two mutually exclusive determinant pairs (d/y and w/r).
The nucleocapsid encloses the viral DNA and a DNA polymerase that has reverse transcriptase activity similar to retroviruses.
The outer envelope contains embedded proteins which are involved in viral binding of, and entry into, susceptible cells.
In addition to alterations at the sites of DNA repair, epigenetic alterations are also caused by HBx recruiting the DNA methyltransferase enzymes, DNMT1 and/or DNMT3A, to specific gene loci to alter their methylation levels and gene expression.
Each altered micro RNA can affect the expression of several hundred messenger RNAs (see micro RNA).A number of bat infecting species have also been described.It has been proposed that a New World bat species may be the origin of the primate species.The viral strains have also been divided into ten genotypes (A–J) and forty subgenotypes according to overall nucleotide sequence variation of the genome.The genotypes have a distinct geographical distribution and are used in tracing the evolution and transmission of the virus.Hepatitis B virus is classified as the type species of the Orthohepadnavirus, which contains eight other species.