The genetic material found in a virus can be either DNA or RNA, but not both. The DNA or RNA can be either double-stranded or single-stranded. The genetic material of the virus contains the instructions necessary for the production of the capsid and spike proteins and also directs the replication of the viral genetic material. Some viruses are able to insert a copy of their genetic material into the DNA of the host cell, thereby ensuring that each time the host cell replicates the viral genetic material is also copied. The insertion of the viral genetic material into the host genome can result in uncontrolled growth of the cell, leading to tumor formation.