SBMH - Snps and Strs


Introduction to SNPs and STRs

This is a complex topic and one that takes a long time to sink in so having a fixed place to go back and review what one learns sure helps. This segment focuses on Y-DNA rather than mtDNA or Autosomal DNA as Autosomal DNA in particular raises a quite different set of interests. So if your interest is Autosomal DNA this info set may not suit you.

There are some simple explanations and some more detailed ones. My advice is always start with the simple then later look at the more complex descriptions so as to avoid too much confusion. It is an exceedingly confusing topic.

The basic building blocks for full understanding can be very deep, but if one starts at the big picture, and then works back to the tiniest part (a 'Base' in a 'Nucleotide'), it does start to all fall into place ...

Genome >> DNA >> Genes >> DNA Molecule >> Nucleotides >> Base >> Base pairs >> Polymorphism in a base >> a Nucleotide becomes an SNP when a polymorphism or mutation in its' base, is seen in 1% or more of the general population >> An SNP can become a Haplogroup >> STRs are repeated clusters of nucleotides and their base pairs >> STR variations between people defines Haplotypes.

Nucleotides and their bases are identified by their position in the DNA string or helix. These are in the millions. The position in Y-DNA is called the Chr-Y position. e.g. The Chr-Y position for Y-DNA SNP named CTS4528 = 15697457. The Nucleotide polymorphism in its' base, at that position, is a change in the base from 'T' to 'C'. If this position's base had not mutated from T to C, then it would not qualify to be called an SNP. SNP simply means means an identified and named (i.e. CTS4528) Polymorphism (mutation) in a Nucleotide (base) at a Single identified position in a DNA chain thus the label S-N-P is created.

A base can be any of A, G, T and C. These four bases used by DNA are actually: Adenine (A) and Guanine (G) which are purines. Thymine (T) and Cytosine (C) which are pyrimidines (but this is now getting too deep).

Teams of scientists at many labs search the DNA chain looking for base mutations (polymorphisms) and when they find one that fits the > 1% of population numbers, they name it. i.e. Chris Tyler Smith found our CTS4528 polymorphism (mutation) and named it. If it had showed up at a very low % (well under 1% of the general population) it may only qualify as a 'Private SNP'. Private SNPs can not become Haplogroups. For more detail on Private SNPs see the menu item on this page.

We CTS4528, L151, DF100 folk, all tend to border just on or below that 1% in the countries we are found in. That is why we don't always show in the published trees.

Read on .....


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