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DNA Decay
Name: Tyler
Status: Other
Grade: Other
Location: Outside U.S.
Country: Canada
Date: Fall 2010
Question:
I'm simply a curious party that heard a rediculous claim
on some U.F.O. documentary and the subject of human/alien hybrids
came up with people talking about a skull they found which they
claim to be a hybrid skull. They said it was over 900 years old, and
that the Mitochondrial DNA in it was strange in that the DNA from
the human mother was there, but not the supposedly alien father. My
question is just to settle my stupid-theory-struck brain. How long
does it take for any recoverable human DNA to decay?
Replies:
Tyler
Human, animal, and plant DNA all same stuff, just in different physical
arrangements.
So that distinction is not relevant.
I did a Google search on "Oldest DNA Found" and found this credible article
that reports the discovery of some bacteria DNA that is 419 million years
old has been found.
http://news.discovery.com/earth/oldest-dna-bacteria-discovered.html
I also found this article from Popular Science magazine that reports the
discovery of the oldest HUMAN DNA "found in the New World" comes from
copralites found in a cave in Oregon. Copralites are dried excrement. This
sample tested at 14,300 years old.
http://www.popsci.com/scitech/article/2008-04/oldest-human-dna-found-americas
Scores of other sites of interest that resulted from this Google
(http://www.google.com) search also showed up and are interesting.
So, to answer part of your question, YES, 900 year old DNA is a possibility.
You are right to ask about the credibility of sources of information
especially in this day of mass media. There are a lot of claims by people
and legitimate organizations (such as pharmaceutical companies) with dubious
motivations and even fraudulent credentials in the public media. I find
especially amusing the Discovery Channel and History Channel's interviews
with "UFOlogists" a new but yet unrecognized scientific field. So when you
are reading articles like this, consider all of the proposed "facts" and
look for inconsistencies, contradictions or really ridiculous claims such as
a 25 year old providing an eye witness report of something that purportedly
happened 100 years ago. Another earmark of a bogus report is the citation
of irrelevant facts in the story to fill in the space required to make the
article long enough for publication. Most of the time these techniques are
not hard to do.
Now for the 2nd part of your question:
I grew up in Roswell, New Mexico between 1947 and 1964. I heard the stories
about the local UFOs and while in the 7th grade, while 9 years old in 1956,
I went to the local library and found some books on UFOs and concluded that
the stories were bogus. I have been listening to these stories for 55 years
now and I have decided to reject all UFO stories until at least one single
piece of physical evidence was presented before I would begin to consider
the possibility of alien visits to Earth. So far I have seen nothing.
Something as simple as a hand calculator prior to 1970 when the rest of us
were using slide rules.
It is always pertinent to ask, who conducted the study and what is the
source of their funding, especially in today's mass media world.
Sincere regards,
Mike Stewart
PS Can you pick out the inconsistency in my answer? Please note my first
citation is from DISCOVER.com while in the next paragraph I question
DISCOVER channel's reliance on testimony from "UFOLOGISTS." But I feel
confident that the article is valid because it presents a lot of consistent
facts.
Tyler,
I think the more amusing part of the tale you tell is about
mitochondrial DNA. Mitochondrial DNA is passed only from the mother
(not the father). So the program's "shocking" claim is actually very
well understood biology.
Although I did not see the program you describe, many similar programs
use a mix of part-truths and willful misrepresentation (like this
program has, describing the paternal mitochondrial DNA as
"inexplicably missing"). I would recommend a large measure of caution
and skepticism in how you approach this.
However, to answer your direct question, there are biological
techniques that can tell you a lot from even highly decayed DNA. DNA
does decay relatively quickly, but even a sample that is 900 years as
you cite could yield important information. It all depends on what
you're analyzing, how you're analyzing it, and the particular degree
of decay from your sample.
Hope this helps,
Burr
Mitochondrial DNA is always inherited maternally.
Mitochondria are organelles inside our cells. They contain
mitochondrial DNA, in addition to the chromosomal DNA.
A sperm cell is small – a nucleus containing 23 chromosomes (in
humans), and very little cytoplasm. It swims as fast as it can to win
the race and fertilize the egg. It does not carry mitochondria because
it travels light and they would slow it down.
An ovum (egg) is larger; it contains 23 chromosomes in the nucleus of
the cell, surrounded by lots of cytoplasm, including mitochondria with
mitochondrial DNA.
(Humans: 46 chromosomes, 23 inherited from Mom and 23 inherited from
Dad; other species have different numbers of chromosomes per cell.)
Occasionally parents of different species might produce a hybrid,
e.g., a male donkey and female horse produce a mule, whose nuclear DNA
is half donkey and half horse, and whose mitochondrial DNA is all
horse. Different species, but still they are earthlings, not aliens.
The fossil skull most likely had an earthling father of the same
species as its mother. Its chromosomal DNA would have been inherited
equally from both parents. Its mitochondrial DNA would have come only
from its mother.
Sarina Kopinsky, MS, CGC (genetic counselor)
DENVER GENETIC LABORATORIES
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Update: June 2012
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