Wow, Victor, I printed out your wonderful explanation below. I think
I am beginning to grasp something. I remember learning something about
chromosomes from school so very long ago. Also, the man next door talked
about some monster criminals, murderers, who were shown to be "YY". I
thought I recalled that men were "XY" and women were "XX". YY's would be
genetic monsters, no? They should be locked up or killed. They are not
really human if they exist. I wonder if my neighbor was joking. I
know that often I don't get the jokes.
Emilie Garcia
Port Orchard, WA ---
----- Original Message -----
Sent: Friday, November 18, 2005 7:50
PM
Subject: [ranchos] mtDNA and other
DNA
Josie,
At the risk of oversimplifying this whole
thing, I'm posting a few
essential concepts about DNA. Please excuse me if
I sound patronizing.
We all have heard that DNA is the blueprint of
life. And it is! Or
to be more exact, each organism's DNA is
its own blueprint of life.
Just think how it is possible to clone an
animal (make an exact
genetic replica) from the DNA found in the nucleus of
a single cell.
And notice that in theory a clone could be made from
practically every
cell in the body, as most cells have a copy of all their
DNA, their
full genome.
Although each cell with a nucleus has their
full genome it only has a
small section of it activated, the specific
section that contains the
instructions that each cell must carry out.
Imagine a huge theater
performance with many, many actors, where every
actor has a copy of
the whole script but some actors only have to read a
few lines or a
few pages at most. So it is with cells; each one has
differentiated
to play a specific role in the body.
We could
say, for practical purposes, that for each cell's role or
function a set of
instructions are written and stored in a gene.
There are many things that
cells do and therefore there are many
genes. These genes in turn are
packaged into chromosomes of which
human cells have 46. These cells
with 46 chromosomes are called
diploid cells.
Since we're not
clones, half of those 46 chromosomes come from each of
our
progenitors. 23 from the father and 23 from the mother to make
23
pairs. Every chromosome is of equal size to its pair except in
males
where the 23rd pair or the XY is an uneven pair. There's a
section in
the Y chromosome that is unmatched in the X chromosome and it
is
called a non-recombining section or segment.
Like I said
above, every cell in the body has two sets of chromosomes
or a total of 46,
but there's an exception: reproductive cells.
Reproductive cells only
carry 23 single chromosomes or half the number
of other cells and they are
called haploid cells. But each of these
chromosomes in reproductive
cells are a combination of the
corresponding chromosome pair in diploid
cells.
Since Y chromosome has an unmatched segment that doesn't
recombine
with the X chromosome, this segment passes almost unaltered
from
generation to generation (but only in the male line or
patrilineal
ancestry). These non recombining sections of the Y
chromosome are
what genetic labs analyze in the now famous YDNA
tests.
The other 22 pairs of chromosomes or the autosomal DNA from
both
progenitors do recombine and shuffle their genes before creating
a
single set of chromosomes in reproductive cells. In other words,
out
of our full genetic material our reproductive cells can only carry
on
and pass to our children half of it. But in contrast to what
we
receive: half from our mother and half from our father, we do
not
necessarily pass on to our progeny the same proportions we
receive
from each. And furthermore, each reproductive cell can have
a
different proportion or combination of genetic material from
our
progenitors, otherwise all our children would be identical.
Makes
sense? That is why it is so difficult to trace the genetic
lineage of
any other of our ancestors besides the Y lineage. Yet, we
can tell
when a child gets a trait from his/her grandpa or her/his grandma,
etc.
Mitochondrial DNA is a whole different story. To start with,
some
people think that mtDNA is part of our chromosomes but it is not.
Like
chromosomal DNA, mtDNA is also in the cells but it is found only
in
the protoplasm not in the nucleus. Mitochondrial DNA is not
strictly
human. Biologists believe that millions of years ago human
cells and
mitochondrial cells created a symbiosis or mutually
beneficial
association. Human cells provide the nutrients
mitochondria need and
these in turn provide the energy the human cells need
to carry out all
their functions. None can live without the
other.
I started out saying that DNA is the blueprint of life and I
was
referring to chromosomal DNA from both parents. But to build a
human
being, like building a house or anything else, you not only need
a
blueprint but also the raw materials and a lot of energy. These
raw
materials and energy always come from the mother, because only
females
get pregnant and give birth. In fecundation and conception
the male
only provides one cell; all the mitochondrial "machinery" is
provided
by the female.
So you can see, mtDNA is strictly inherited
thru the maternal line.
And when a mutation ocurrs in mtDNA all offspring
inherit the same
distinctive mutation. But mutations in mtDNA are
much more rarer than
mutations in YDNA, therefore a single mismatch in
mtDNA can mean a
shared ancestor many, many generations ago, beyond the
conventional
genealogical framework. This is our deeper ancestry
link!
Saludos,
Victor
--- In ranchos@yahoogroups.com,
"Josie T. Trevino" <Josiett3@s...> wrote:
>
> Hi!
>
> Someone once explained to me that the mtDNA results
were, in some
cases, the
> result of Spaniards marrying the "local
girls" ........is this what
you are
> referring to,
Arturo? I do not understand these numbers.....I am
just
> trying to make heads or tails out of it......and to justify the
$$$$
I spent
> to get these numbers! :-)
>
Seriously, I don't mind spending the money if it will give me some
clues
as
> to my ancestors, the migration pattern they followed, etc. I
have only
> researched about three or four generations on my Dad's
maternal line and
> three or four on my Mom's maternal and paternal
lines so I have a
long way
> to go. I have been focusing on my
Dad's paternal Trevino lineage and go
> "way back" to about the 1400s in
Spain.
>
> I really enjoy reading the messages
everyone is sending regarding
Y-DNA and
> mtDNA because I am slowing
learning a little here and there. What I
really
> like is
finding out that I have matches to a few in this group, Linda,
> Victor,
Arturo and an exact match with Ed! Even though I have never
met
any
> of you in person I do feel a connection! The only
grandparent I
knew was
> my Mom's father and he died when I was 7
years old. My other
grandparents
> died before I was
born. I only have one brother so you can see that my
> familia is
very small.......maybe that is why I am always looking
for "mi
>
gente!" I have met several primos and primas (live ones!)
through
> genealogy and it feels good when we share information and
discover
that our
> great-grandparents were brothers/sisters and here
we are digging up
their
> information!
>
>
It would be wonderful if a group were started concentrating on
mtDNA.
>
> Josie in San Antonio
>
|
|
by Date 
-