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What is the difference between Polymorphism and SNP - (Dec/31/2011 )

What is the difference between Polymorphism and SNP? And because of which one of thez two, is responsible for diseases?


SNP is just one type of polymorphism and involves only one nucleotide. Any type polymorphiism can be associated with disease.


But it is becoz of polymorphism only, each individual differ from each other, then how polymorphism contributing to diseases.


You should read this paper Attached File


DDLJ on Sat Dec 31 16:50:47 2011 said:

But it is becoz of polymorphism only, each individual differ from each other, then how polymorphism contributing to diseases.

1. SNP is a type of polymorphism
2. polymorphism just means that the DNA is "different" due to a mutation for example, a base switch (T and not G for example at a certain place)
3. I think its clear that when you normally have GATC and due to a SNP you have all of a sudden AATC that this change in sequence can cause a disease..
(another example: take for example a SNP in a gene coding for a protein and because of this SNP you get a stop codon rather then a codon for an AA , then what happens? translation will stop and you will not form that protein.. result: disease (or not, its not always the worst case scenario ofcourse)

And that paper might help indeed.


each person has their own polymorphism .. although we are human but we are difference ....
SNP is the altheration in your genome seq. that may or may not be the cause of your disease
depend on where it occur and if it occur in coding seq. some ime it can change your amino acid or cannot...
and althoug it change your amino acid but if it not effect to the protein function it cannot cause the disease...
In the case ,SNP can cause disease such as sickle cell anemia....
remember that when the symptom or disease occue it mean that our body cannot control or cannot compensate to be the normal condition.....


Polymorphism originaly meant something that differs from person to person (or individuals within other species in general), and is considered normal and common. Like, there are known mutations, that are causes of diseases, cancer or so. These are not called polymorphisms, but causative mutations. And of course these are also rare. Sickle-cell anemia mutation would be hardly called SNP, at that time.

Many things can be polymorphic, single nucleotide polymorphisms (SNPs), repeat lengths, bigger sequence changes (insertions/deletions), immune system antigens and receptors... but they all need to be generaly present in population and not directly and clearly linked to a disease. (on the basis of highly polymorphic regions of short tandem repeats in genome is based the person identification and paternity testing, because no person has all of the regions of the same length).
So originaly SNP, was not connected to a disease.

However nowadays things get more complicated. As far as I now a sequence variant is considered a "real" SNP if there is some level of "commoness" in the population, like.. 5 %. But the more and more SNPs we know, we found out that many of them are actually associated with a disease (that means, that person with this variant is more likely to have a disease, than person without it, but there is no clear functional link, that this would cause the disease in 100 %, in in vitro model, animal models, etc.). As many of the diseases are caused by combination of factors (in reallity I would say all of them are) some SNPs may just help to develop a disease but can be pretty common at the same time.
Theory is, if some sequence variant is causing disease, the bearers are less likely to reproduce, so the frequency of the "bad" variant will be very low in population, selected out. Of course if the selection is not that hard, the variant not that often harmful or sometimes harmful sometimes even beneficial, the frequency in population could be even quite high, like those 5 - 10 % for example.
Of course, if someone was just screening people, he would initialy consider this variant a SNP, but later it can be found that it has a role in some pathology.

The more we know about cell systems, and the more genomes are we sequencing, the thin line between SNP (a "common" variant) and a causative mutation is getting more blurred. The SNP database for example, now hold every variation that was recorded from numerous whole genome sequencing studies, and there are variants or "mutations" there, that would be hardly considered either common or benign (like the rs77375493 entry, which is a causative acquired mutation, a direct cause of 98% of polycythemia vera, still... in a SNP database..).

So, to sum it up. Now it's really difficult to really specify what SNP is and what isn't. The original definition is depricated, since things become more complex. Some SNPs are considered just "one or other" variants, usualy when you have frequency around 50/50 and have no or very weak associations to anything, some could be very rare and with unclear connection to diseases. To even more complicate this, not only coding sequence variations can have some effect, variations in promoter, regulatory sequences, or just "some" regions we re not sure what function they have, these are usually called "functional SNPs".
Also it has been long thought, that coding sequence SNPs, that doesn't result in any change in the amino acid sequence (silent SNPs), are the "real" SNPs, having no effect at all.. seems this is not true 100%, it may doesn't have a direct effect on protein it codes, but differences in DNA (or mRNA) sequence, can have regulatory functions in addition, or higher succeptibility to mutation into differen variant or DNA damage or so. So some of these can be also "functional SNPs".

So probably now, every variant (single nucleotide) that's observed in person, is most likely to be called "SNP". But for some well established mutations, this is never actually used.
As time changes, today a SNP, causative agent tomorrow..


Thank you very much Brain on a stick