Y chromosome DNA, along the line of fathers

The Y chromosome is possessed only by men. It comprises ~ 57,772,955 base pairs, a fraction of these have been studied. The Y chromosome is passed integrally from father to son. The father received it from his own father and so on back to a patriarch who was the first to possess the mutations that characterize his chromosome and that he transmitted to his sons. Mutations occur regularly along the chain of transmission from father to son. The presence of some mutations in the Y-DNA can therefore be used to follow lines of men.

The variations found in the Y-DNA are examined through two types of markers:

1. STR, for Short Tandem Repeat.Specific areas which comprise between 120 and 200 bases, most of the time adjacent on the the Y chromosome, are examined for the presence of a given repetitive pattern.Thus, the motif GAAA (Adenine Guanine Adenine Adenine) repeats between 13 and 20 times at a place marker called DYS458 in the DNA of a men.
Y-DNA tests based upon STR will examine between 12 and 111 (actually 114) of these sites or markers on chromosome Y. The STR values will form a signature.

The next figure shows a Y-DNA signature composed of 45 STR markers, some of these markers are multiple, composed of 2 or more values.


The price of y-DNA tests at FTDNA

Number of markers Price
12 99$
25 124$
37 149$
111 339$

A test comprising 25 markers is good to begin with. Other markers can be added as needed thereafter.

2. Singular Nucleotide Polymorphism (SNP). SNPs are mutations that occur at particular locus in a generational event. A locus is a particular nucleotide address on the chromosome. The SNP is thereafter transmitted hereditarily integrally to male descendants.
A given locus can show a base value (A,G,T,C) which is ancestral or derived when mutated. When derived it thus serve as a SNP. Thus, in the figure below, a C was replaced by a T in a DNA strand and the complementary base is self-assembled by additional attraction on the opposite strand.
Examination of a corresponding locus through genetic testing can thus permit to determine if its state is ancestral or derived and thus to follow various lines of men.
Moreover, when SNPs are sufficiently widespread or general allow genetists to use them to build phylogenetic lineages similar genealogies,thus contributing to the establishment of a taxonomic classification composed of haplogroups or clades and their subdivisions called subclades.


When you will receive your Y-DNA test results from FTDNA, a computer program will have been used to predict its haplogroup belonging, based on its ressemblance with other signatures in a large population. However, the haplogroup affiliation and sousclade subdivision should be confirmed in a specic test called *Deep Clade*. This test costs $139. Once your haplogroup known precisely, thereafter, when new SNP will be discovered, testing for it will cost $39 per SNP. The result of the test will show whether it is ancestral or derived, thus indicating the position of your y-DNA in the phylogenetic tree.

To get an idea of the usefulness of SNPs to study the phylogeny of the human Y-DNA, visit your personal page at FTDNA and click on the link labeled *haplotree*.

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