The Human Genome : An Historical Record Of Endogenous Retroviruses

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Background Information:
The human genome represents an historical record of Endogenous Retroviruses that currently impact the human species as these ancient retroviruses integrated themselves into the human genome long ago. Human endogenous retroviruses, or HERVs, comprise a significant part of the human genome with roughly 100,000 elements and fragments, forming as much as 8% of the genome, however their abundance in the genome had not been previously predicted in early studies (Shors, K). HERVs have been associated as cofactors in several chronic forms of cancers and autoimmune diseases such as HIV, and neurological diseases (Shors, K). Even though the association of HERV expression and human disease is prevalent, many appear to be
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These are the endogenous viruses and some individuals can have thousands of copies of these A-type viruses in their chromosomal DNA. B-type viruses have an eccentric core and the mammary tumor viruses exclusively possess this structure (Cloyd, M) . These viruses exist as endogenous and exogenous viruses and when expressed can cause mammary tumors. C-type viruses have a central electron core (Cloyd, M) . Most of the oncoviruses and endogenous viruses are C-type viruses. The D-type viruses have a rod-shaped core and consist primarily of lentiviruses (Cloyd, M) . HERVs are a subclass of a gene known as transposon. These genes can be packed and moved within the genome to serve a vital role in gene expression and regulation. HERVs have been grouped into three broad classes, based on the sequence similarities, which are broken into subgroups based on the specificity of their tRNA binding site. Class I HERVs are related to gamma retroviruses such as murine leukemia viruses (Griffiths, D). Class I includes the subgroups of HERV-W and HERV-H. Class II HERVs are related to beta retroviruses such as mammary tumor viruses and include several subtypes of HERV-K elements (Griffiths, D) . Class III HERVs are related to spumaretrovirueses and subgroups include HERV-L and HERV-S (Griffiths, D) . Class I and class III are the oldest groups, seen in primitive lineage, and class II includes those active most recently. HERVs
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