Epigenetic theories of homosexuality concern the study of
changes in gene expression or cellular phenotype caused by mechanisms other
than changes in the underlying DNA sequence. Epigenetic examines the set of
chemical reactions that switch parts of the genome on and off at strategic
times and locations in the organism's life cycle. Instead of affecting the
organism's DNA sequence, non-genetic factors cause the organism’s genes to
express themselves differently. DNA in the human body is wrapped around histones,
which are proteins that package and order DNA into structural units. DNA and
histone are covered with chemical tags known as the epigenome, which shapes the
physical structure of the genome. It tightly wraps inactive genes on the DNA
sequence making those genes unreadable while loosely wrapping active genes
making them more expressive. The more tightly wrapped the gene, the less it
will be expressed in the organism. These epigenetic tags react to stimuli
presented from the outside world. It adjusts specific genes in the genome to
respond to humans' rapidly changing environment. The idea of epigenetic and
gene expression has been a theory applied to the origins of homosexuality in
humans. One team of researchers examined the effects of epi-marks buffering XX
fetuses and XY fetuses from certain androgen exposure and used published data
on fetal androgen signaling and gene regulation through non-genetic changes in
DNA packaging to develop a new model for homosexuality.
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