K Barrett wrote:
Another thing was - I'm vaguely recalling this - that a lot of DNA in the
human genome is from viruses that have attached to it in the dim past,
raising the question(s) how do they know and what then is human?

In many cases, old viral sequence has features that scream "virus"
(long terminal repeats, etc) or can be identified by homology to
current, active viruses. But sometimes, it's not obvious that there is
a bright line dividing "human" and "virus." Viruses can pick up human
sequences. The reverse can also happen: sometimes, the evolutionary
history of a human gene includes insertion of viral elements. For
instance, the salivary amylase gene appears to have been generated when
a retroviral sequence inserted into the promoter region of an ancestral
pancreatic amylase gene. The retroviral sequence is what causes the
amylase gene to be expressed in salivary glands. So, in this case, the
sequence of a virus has become human.

Thanks again! This is great. Like having my own little continuing
education class.

Science really has exploded since I was in school. Recently I googled
Robert J. Griesbach USDA in order to read if he had any papers published on
microfungus (a question from a different thread here and more orchid
related) and came up with a list of abstracts for his papers, someof which
dealt with color (blue) in phalaenopsis. One google search on terms led to
another and another and I came away impressed at how some very minute
research leads to greater knowledge.

Anyway,

Thanks again for filling me in. I appreciate it.

K Barrett
wrote in message
oups.com...
K Barrett wrote:
Another thing was - I'm vaguely recalling this - that a lot of DNA in the
human genome is from viruses that have attached to it in the dim past,
raising the question(s) how do they know and what then is human?

In many cases, old viral sequence has features that scream "virus"
(long terminal repeats, etc) or can be identified by homology to
current, active viruses. But sometimes, it's not obvious that there is
a bright line dividing "human" and "virus." Viruses can pick up human
sequences. The reverse can also happen: sometimes, the evolutionary
history of a human gene includes insertion of viral elements. For
instance, the salivary amylase gene appears to have been generated when
a retroviral sequence inserted into the promoter region of an ancestral
pancreatic amylase gene. The retroviral sequence is what causes the
amylase gene to be expressed in salivary glands. So, in this case, the
sequence of a virus has become human.