>
> Victor.......is this the complete message? It appears that you left off in
> the middle of a sentence......Thanks! Josie
>
> _____
>
Josie, it looks like the message got truncated. Below is a copy of that same message.
----------------------->
That's a keen observation and a good question about the number of differences in our mtDNA in relation to the CRS reference.
Let's start by saying that the CRS (Cambridge Reference Sequence) is just an arbitrary reference selected by some team of geneticist that were among the first to study the genetic sequences of mitochondrial DNA. They decided to use the sequence of one of their subjects as a comparison reference, maybe one of their own samples, who knows?. The selected mtDNA belongs to haplogroup H, the most prevalent haplogroup in Europe. Therefore many European persons who get tested have few differences if any with the CRS reference.
Next, what the commercial tests show us about our mtDNA is not the whole sequence of mtDNA but just one or two regions: HVR1 and HVR2 (Hyper Variable Regions). Supposedly these two regions don't have any medical implications so having a few more or a few less mutations is not very significant. But that is not always the case in the remainder of the mtDNA molecule. Some mutations could be good while other mutations could be bad in terms of health and disease.
To better understand what we're talking about let's use an analogy. DNA sequences are a string of chemical bases limited to four possible values A, T, C and G (Adenine, Thymine, Cytosine and Guanine). So think about a collar made up of coloured beads. The beads come in just four colors: red, yellow, green and blue. Now look at the following comparison between CRS and my own mtDNA in the 16310-16320 segment:
CRS Reference: TACATAAAAC
My mtDNA: TACATAAAGC
The difference in my bead collar is obvious at the 9th position or 16319; an A has been replaced by a G.
Therefore, if I have two or more mutations in my mtDNA than you it probably means that somewhere along the way some of my ancestress acquired extra mutations while yours remained unchanged. I said probably because there is such a thing as "back mutations" where a mutation reverts back to its original value or state but these are supposed to be even rarer than regular mutations. We don't know yet exactly all the events that can cause these mutations to ocurr but we can sure use them to trace the branches of our big motochondrial tree.
Saludos Cordiales,
Victor
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Maria, Your first thought is correct. You and your brother share the same mitochondrial DNA so there's no need for you to take the same test. If you were testing autosomal DNA then your results and your brother's could be slightly different, but the usefulness and accuracy of such tests is very limited for our genealogical purposes and it is not recommended. With your brother's Y-DNA and mt-DNA tests you will know your paternal Y-chromosome lineage and your maternal mitochondrial lineage. The next logical step if you wanted to research your genetic origins any further would to be to test either a maternal uncle's Y-DNA or a paternal aunt's mt-DNA, or both. We have to remember that genetic lines (Y-DNA & mt-DNA) branch out and multiply exactly like a genealogical tree. We start with two parents and then four grandparents and then eight great-grandparents. When we discover one of our genetic lines there is one ancestor at each generational step that has the same genetic line just like patrilineal surnames, with the difference that in old times people used to change their surnames but here there's no way we can change one's haplogroup. If we had a way to genetically test all our lines, as branches in our tree multiply going back in time it is very likely that some genetic lineages would appear repeatedly as some families tended to intermarry with a limited number of families, particularly when population was scarce. Whenever this has happened in ancient times these events are called a "bottle neck" event and are reflected by a lesser genetic diversity. Saludos, Victor --- In ranchos@yahoogroups.com, "readysetgo95814" <mcortez3@g...> wrote: > > > Victor, > > Thanks for the wonderful explanation on DNA. It didn't come across as patronizing at all. > > I have a question about something you stated for you or anyone else who may know the answer: "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..." > > My brother is taking both the yDNA and the mtDNA tests. I was thinking that since we come from the same set of parents there would be no benefit to having my DNA analyzed, but after reading the above I am thinking otherwise. Perhaps it would be more valuable to have a great uncle or aunt from both sides of the family (since all my grandparents are dead) have their DNA analyzed. > > Maria
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Victor,
Thanks for the wonderful explanation on DNA. It didn't come across as patronizing at all.
I have a question about something you stated for you or anyone else who may know the answer: "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..."
My brother is taking both the yDNA and the mtDNA tests. I was thinking that since we come from the same set of parents there would be no benefit to having my DNA analyzed, but after reading the above I am thinking otherwise. Perhaps it would be more valuable to have a great uncle or aunt from both sides of the family (since all my grandparents are dead) have their DNA analyzed.
Maria
--- In ranchos@yahoogroups.com, "v.h.villarreal" <raices_regias@y...> wrote:
>
> 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
> >
>
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That's a keen observation and a good question about the number of differences in our mtDNA in relation to the CRS reference.
Let's start by saying that the CRS (Cambridge Reference Sequence) is just an arbitrary reference selected by some team of geneticist that were among the first to study the genetic sequences of mitochondrial DNA. They decided to use the sequence of one of their subjects as a comparison reference, maybe one of their own samples, who knows?. The selected mtDNA belongs to haplogroup H, the most prevalent haplogroup in Europe. Therefore many European persons who get tested have few differences if any with the CRS reference.
Next, what the commercial tests show us about our mtDNA is not the whole sequence of mtDNA but just one or two regions: HVR1 and HVR2 (Hyper Variable Regions). Supposedly these two regions don't have any medical implications so having a fewer more or a fewer less mutations is not very significant. But that is not always the case in the remainder of the mtDNA molecule. Some mutations could be good while other mutations could be bad in terms of health and disease.
To better understand what we're talking about let's use an analogy. DNA sequences are a string of chemical bases limited to four possible values A, T, C and G (Adenine, Thymine, Cytosine and Guanine). So think about a collar made up of coloured beads. The beads come in just four colors: red, yellow, green and blue. Now look at the following comparison between CRS and my own mtDNA in the 16310-16320 segment:
CRS Reference: TACATAAAAC
My mtDNA: TACATAAAGC
The difference in my bead collar is obvious at the 9th position or 16319; an A has been replaced by a G.
Therefore, if I have two or more mutations in my mtDNA than you it probably means that somewhere along the way some of my ancestress acquired extra mutations while yours remained unchanged. I said probably because there is such a thing as "back mutations" where a mutation reverts back to its original value or state but these are supposed to be even rarer than regular mutations. We don't know yet exactly all the events that can cause these mutations to ocurr but we can sure use them to trace the branches of our big motochondrial tree.
Saludos Cordiales,
Victor
--- In ranchos@yahoogroups.com, "Josie T. Trevino" <Josiett3@s...> wrote:
>
> Victor......thanks for the explanation on DNA, and you do not sound
> patronizing. I appreciate the detail that you provide regarding DNA. I
> have been so involved in searching for my ancestors that I never gave DNA a
> thought until now. This adds more flavor to the research that I love!
>
> I noticed that I only have four "HVR1 differences from CRS" (mutations) in
> my mtDNA results posted on the database for Family Tree DNA while others
> have five, six and more. What does this indicate? I understand that the
> CRS is used as a basis for comparison with mtDNA and that, in my case, I
> have four instances of differences from the CRS.......what I do not
> understand is......is this a good thing? :-) Am I trying to read too much
> into this?
>
> Thanks again, Victor, for your help......and thanks to the other members of
> this group who have helped me! I appreciate it!
>
> Josie in San Antonio
> _____
>
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Emilie, I know we're straying off topic, but just a brief comment about your reply. What your neighbor may have been talking about is something called a trisomy, a rare kind of chomosomal anomaly where there's an extra chromosome in one of the numbered pairs. So instead of the normal XY in a male this individuals have an XYY. It is possible that such individuals have exceptional characteristics, either for good or evil. One could just as easily become a serial criminal or a super bright scientist. Victor --- In ranchos@yahoogroups.com, "Emilie Garcia" <auntyemfaustus@h...> wrote: > > 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 ---
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