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Old 01-22-2003, 12:11 PM
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Can scientists determine whether a DNA sample is from a human being?


Given sample A and sample B of DNA, can a it be determined with a scientific certainty that, say, sample A is human and sample B is simian?
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Old 01-22-2003, 12:38 PM
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Yep.
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Old 01-22-2003, 12:39 PM
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Thanks, Dex. A follow-up, please. Is the DNA of a fetus the same as the DNA of its mother?
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Old 01-22-2003, 12:44 PM
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The fetus derives 1/2 of its DNA from its Mother and 1/2 from its Father.
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Old 01-22-2003, 12:45 PM
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Quote:
Originally posted by Libertarian
Thanks, Dex. A follow-up, please. Is the DNA of a fetus the same as the DNA of its mother?
Half of the nuclear DNA is. The other half is from the father. All of the mitochondrial DNA is from the mother.

Bear in mind that much of the DNA of both parents - more than 99% - is identical anyway.
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Old 01-22-2003, 12:46 PM
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Nope.

The DNA of a fetus is a combination of the DNA of its mother and father. This is why paternity tests work.

The only humans that have identical DNA are identical twins, and clones. So, in theory -if you were a twin (or a clone) you could be convicted/acquitted on the basis of your twin's (clone's) DNA.

The DNA of animals is sufficiently different from human DNA that you could not be convicted/acquitted on the basis of your dog's DNA.

Does that help?
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Old 01-22-2003, 01:13 PM
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What could both you AND your dog be charged with? Littering?
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Old 01-22-2003, 01:14 PM
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Is this leading to an abortion discussion?

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Old 01-22-2003, 01:16 PM
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I remember reading somewhere that over 90 per cent of human DNA is the same as that of the chimps (our closest relative among the primates). I can't remember, 96%, 98%? Whatever the difference is, it's enough to dedect, however.
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Old 01-22-2003, 01:23 PM
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The trouble with the abortion angle is that it is not clear that every entity with human DNA is a person. A hair sample or a liver biopsy sample has human DNA, but is not a person.

There is the famous example of HeLa cells. These were human cells taken from a cancerous tumor and used for research purposes. The cells were so agressive that they are sometimes found invading and contaminating other tissue cultures. In effect they are protozoans with 100% human DNA.

See:
http://www.madsci.org/posts/archives...1113.Cb.r.html
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Old 01-22-2003, 01:31 PM
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We share more than 90% of our DNA with chimpanzees, but I, too, don't recall the exact figure.

We share significant portions of our DNA with nearly all animals, anyway. It's the wonders of evolution and the fact we have never had a reason to make a serious change. In fact, our basic bodyplan (long torso with digestive tract running right down the center) was first evolved by ... you guessed it ... worms. Remove the appendages and a human will still live, something we inherited from our wormy ancestry.
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Old 01-22-2003, 01:47 PM
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Looking at this link http://www.answersingenesis.org/docs2002/1125dna.asp
I don't think typical DNA tests would be able to differentiate the two. It would take a karyotype of the entire genome to detect the differences. Remember that DNA testing uses the "nonsense" areas of the chromosome and that it can determine if the DNA came from a single source it tells nothing about what that source is.
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Old 01-22-2003, 02:29 PM
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Did you really post a link to ANSWERS IN GENESIS?!?!?!?

Do you know what the word "karyotype" means?

This message board is supposed to fight ignorance, not perpetuate it.
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Old 01-22-2003, 02:36 PM
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Quote:
Originally posted by dauerbach
I don't think typical DNA tests would be able to differentiate the two.
Why not?

Quote:
It would take a karyotype of the entire genome to detect the differences.
I don't think you know what "karyotype" means.

Quote:
Remember that DNA testing uses the "nonsense" areas of the chromosome and that it can determine if the DNA came from a single source it tells nothing about what that source is.
What do you mean, exactly, by "DNA testing"?
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Old 01-22-2003, 02:58 PM
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Ack, I didn't realize where I was and just glanced at what it said. The facts concerning similarity of genotypes is accurate (greater than 95%) , and I had no idea that it was an anti-evolution site. Shows what happens when you try to play at work.

Yes, I know what a karyotype is and said genome, but meant comparing the appearance of all the chromosomes in an intact nucleus.

By DNA testing I meant what is currently used in the legal system, either PCR or RFLP. Both tests give no information as to what species the sample came from.
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Old 01-22-2003, 03:10 PM
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Quote:
Originally posted by Lemur866
The trouble with the abortion angle is that it is not clear that every entity with human DNA is a person. A hair sample or a liver biopsy sample has human DNA, but is not a person.

There is the famous example of HeLa cells. These were human cells taken from a cancerous tumor and used for research purposes. The cells were so agressive that they are sometimes found invading and contaminating other tissue cultures. In effect they are protozoans with 100% human DNA.

See:
http://www.madsci.org/posts/archives...1113.Cb.r.html
Does biology define the term "person" or "human being"? Or must that be defined by a branch of philosophy other than science? Say, ethics, maybe?
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Old 01-22-2003, 03:17 PM
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Quote:
Originally posted by dauerbach
Ack, I didn't realize where I was and just glanced at what it said. The facts concerning similarity of genotypes is accurate (greater than 95%) , and I had no idea that it was an anti-evolution site. Shows what happens when you try to play at work.
OK, that's better. Given the nature of the link, I wanted to know where you were coming from.

I agree with you, the info you linked to is surprisingly correct considering that it's posted on a creationist site. The point that the percentage of similarity between chimps and humans varies with what kind of differences are considered is perfectly valid.


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By DNA testing I meant what is currently used in the legal system, either PCR or RFLP. Both tests give no information as to what species the sample came from.
They don't give species information in and of themselves. However, they can be used to identify species when used in conjunction with a data bank. Here is an example of using PCR to determine the species of a sample of tuna.
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Old 01-22-2003, 03:25 PM
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Quote:
Originally posted by Libertarian
Does biology define the term "person" or "human being"? Or must that be defined by a branch of philosophy other than science? Say, ethics, maybe?
The latter.

Biologists may try to define, in scientific terms, what is meant by an "individual," a "species," a "member of the species Homo sapiens, etc., but even these definitions may be open to dispute. I do not think that "person" or "human being" are, by their nature, scientific terms.
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Old 01-22-2003, 04:10 PM
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You can define "human being" scientifically, by saying that any member of the species Homo sapiens is a human being. And we can use the biological species concept. But that is not satisfactory ethically, since it would mean that people who can't interbreed would not be human!

In my opinion, "Personhood" is a legal and/or ethical concept, not a scientific concept. Science can give you information on which you can base your ethical judgements.

For instance, we could ethical judge dolphins and elephants and intelligent robots to be "people", even if they aren't humans. And going the other way, we don't judge human tissue to be a person neccesarily.

I'm pretty comfortable in not having a rigorous definition of personhood, since I doubt human competence in making that definition. There will always be cases that no one considered when making the rules. Although all persons must have some sort of brain activity, I still don't want anencephalic babies to be judged *things*.

The bottom line is that biology can reveal that there is no sharp demarcation in these categories. A single cell taken from your finger is not a human being. But is a single fertillized egg cell? What exactly is the difference? Is there a difference if we take the nucleus from your finger cell and insert it in a fertillized egg cell? Are identical twins one person or two? How about conjoined twins that share a body but have two heads? Would it make a difference if one of the twins had brain damage and was in a permanent vegetative state and the other wasn't? What about conjoined twins with two bodies but one head? How about a person with an extra leg?

For the vast majority of human beings there isn't any confusion between where the individual starts and stops. But for many other species this isn't the case. Take grass...grass usually reproduces by new blades springing up from underground rhizomes. This means that the new blades are genetically identical to the parent blade. But are they new individual grass organisms, or is the individual organism the patch of grass that includes many blades, like a tree contains many leaves? Does it make a difference if you take a hoe and cut the patch in two?

Anyway, the point of all this rambling is to demonstrate that personhood and individuality are ethical decisions informed by science, not scientific decisions.
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Old 01-22-2003, 05:03 PM
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While we have the various DNA test experts assembled, allow me to slightly hijack thusly:

Could the common PCR or RFLP tests distinguish me from my non-twin brother? My sister? My half-brother or -sister, either with the same mother or father?

The specific situation which occurrs in the screenplay I'm writing is that a man attempts to fake his own death by substituting the burned-beyond-recognition body of his brother and assuming his identity. Would a DNA test be able to tell the difference?
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Old 01-22-2003, 05:44 PM
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Quote:
Originally posted by vibrotronica

Could the common PCR or RFLP tests distinguish me from my non-twin brother? My sister? My half-brother or -sister, either with the same mother or father?
...
Would a DNA test be able to tell the difference?
Yes, yes, yes, and yes. It all depends on which primers you choose to use, and what part of the DNA you want to amplify.
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Old 01-22-2003, 08:26 PM
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OK, just so I don't have to wade through the bullshit after Googling, what does karyotype really mean in a biological context?
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Old 01-22-2003, 09:38 PM
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A karyotype is a picture taken of a cell's nucleus where the chromosomes (tightly bundled strands of chromatin) are visible. It is usually taken during the beginning stage of mitosis and a stain may be used to highlight the chromosomes. In a good karyotype, you can differentiate each individual chromosome.

Given three karyotypes, one from a human, one dog and one fruit fly, it is easy to tell which karyotype belongs to which animal based on the number of chromosomes.

Karyotypes may be used to detect the sex of an individual, and even diseases related to chromosome number, e.g., Klinefelter's Syndrome.
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Old 01-23-2003, 08:09 AM
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They don't give species information in and of themselves. However, they can be used to identify species when used in conjunction with a data bank. Here is an example of using PCR to determine the species of a sample of tuna.

This isn't really determining the species of tuna de novo, but rather comparing the electrophoresis pattern with knowns. As such it is identical to the way DNA fingerprinting is used in humans. Throw human or simian DNA into the array and all you will know that it is not from one of the given species of tuna. You will not know if it is mammalian, reptilian, fish, etc. Perhaps, if you had human and simian standards, and carefully chose the restriction enzymes you could differentiate human from ape, but I still question even that. Most of the differences in the two genomes would be histocompatability sites, with perhaps a HOX or two different, but since the technology is really comparing junk stretches of the genome I still doubt that you could differentiate the two. Karyotype would easily do it, I am still looking for cites to support my contention that fingerprinting would not.
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Old 01-23-2003, 09:27 AM
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dauerbach, I think you are simply arguing semantics at this point. We do have human and simian standards for comparison, and given this a given sample could be identified as being from one or the other (or from neither). This is the question posed by the OP, not whether a sample could be identified without comparison.

In any case, you have the same problem with karyotype - unless you have a reference to compare it to in detail, all you can say is that the sample does or does not have a particular chromosome number or morphology. This in itself does not give any more information about species identity than DNA analysis does.
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Old 01-23-2003, 10:44 AM
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Colibri,

I don't think we are arguing semantics. I look at the question like this: You find blood or semen or whatever at a crime scene. You process the sample and run it through any type of DNA fingerprinting routine you want. Is there any way to determine that the DNA is from an ape. I say no. If you are allowed to look at the karyotype I say why bother, just look at the criminal. If it is an ape it would be readily apparent.
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Old 01-23-2003, 12:24 PM
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Quote:
Originally posted by dauerbach
You find blood or semen or whatever at a crime scene. You process the sample and run it through any type of DNA fingerprinting routine you want. Is there any way to determine that the DNA is from an ape. I say no.
Well, then, all I can say is you are incorrect. I have already provided an example of how PCR can be used for species identification in tuna. Similar techniques could be used to match simian DNA to species, or at least to conclude that it's simian rather than some other taxon. The OP is not concerned with whether species IDs can be made de novo, but whether they can be made at all.
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Old 01-23-2003, 12:26 PM
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No, that's not correct. It is true that you couldn't tell it was ape blood just by looking at it, or random DNA tests. But if you suspected it was ape blood, you could compare the DNA of the blood sample to a blood sample taken from a known source, a chimpanzee. You absolutely CAN determine which species provided the blood. Currently I believe it would require a brute force approach to determine the species. First you test if it is a chimpanzee. If not, test if it is a gorilla. If not test if it is an orangutan. If not, test if it is a siamang.

Of course, these tests are really done in reverse, just like the paternity tests they do on Montel Williams. They can tell you absolutely that the specimen is NOT from such and such a person, or from such and such a species. Do that often enough from enough loci and you can get any arbitrary confidence level that it IS from a specific person or species that you want.
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Old 01-23-2003, 01:20 PM
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Ok, I tried to find this on the web and could not. Could I have some cites please.
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Old 01-23-2003, 01:36 PM
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Quote:
Originally posted by dauerbach
Ok, I tried to find this on the web and could not. Could I have some cites please.
I gave you a cite.
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Old 01-23-2003, 01:59 PM
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Thank you colibri. Finally, and at last I am satified and admit I am wrong.
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