Jordan Surname DNA Project: Definitions
Alleles -- One of the different forms of a gene of DNA sequence that can exist at a single locus.  Alternatively, one of several alternate forms of a gene occupying a particular location on a chromosome.

Chromosome -- Is composed of DNA, which itself is composed of four (4) nucleotides:   A (adenine);  T (thymine);  C (cytosine);  and G (guanine);  Chromosome = thread-shaped structure occurring in cell nucleus, which transmits hereditary characteristics.

DNA -- Deoxyribonucleic Acid.

DYS -- D = DNA:  Y = Chromosome;  S = (STR) Single Tandem Repeats;  The DYS numbering scheme (e.g. DYS388, DYS 390) for the Y-STR haplotype loci is controlled and administered by an international standards body called HUGO, Human Gene Nomenclature Committee based at the University College, London.

These results compare individuals to see how closely or distantly they may have shared a common ancestor.  The estimated rate of mutational change is estimated to be approximately one change per 500 generations for these loci (the locations on the Y chromosome).  Since our test uses 12 different loci, it is reasonable to expect a change to occur every 40 or so generations;  however, these changes can take place at any time.

Gene -- The fundamental and functional unit of heredity.

Haplotype -- Refers to a single or unique set of chromosomes.  A set of closely linked alleles (genes or DNA polymorphisms) inherited as a unit.  Different combinations of polymorphisms are known as haplotypes.

Haplogroup -- Haplogroups are groupings of individuals with the same genetic characteristic such as restriction enzyme recognition sites or deletions at the same location on the DNA. A haplogroup is a "Distinct Y chromosomes, defined solely on the basis of unique mutation events (UME) character states, are designated as haplogroups." Each haplogroup consists of a variable number of Y chromosomes that share the same UME character state but vary in Y-STR haplotype.(from Peter de Knijff). More generally, haplogroup can be defined as a cluster of similar haplotypes. Wilson's paper (Helgason's were slightly different) gives the "modal" haplotype (the single most common haplotype) for his set of subjects in haplogroups 1, 2, and 3 (the most common European haplogroups):
The above are modal haplotypes; see Wilson's study. The HG2 haplogroup is the Nordic group. If your results match one of the above patterns, or differ in just one marker, we feel some confidence in classifying your haplogroup. For a list of haplogroups, see Y Chromosome Consortium [Y chromosome haplogroup tree and nomenclature].

Results that match HG2 indicate a strong connection with Nordic (Scandanavian) countries. The HG2 Nordic Haplogroup is one of two Nordic Haplogroups. This indicates that the family of origin were probably of Viking descent or a male ancestor was of Viking blood.

Kohanim Project -- See the website located at Also as well, see Dr. Michael Hammer above.

Loci -- The position that a given gene occupies on a chromosome. (Plural)

Locus -- A specific location on a chromosome. (Single)

MH -- Modal Haplotype = Any person who matches exactly the alleles found to be most common among the descendants of a person.  A person who matches 11 alleles whiile being only one off in only one (1) loci, will be considered to be in the haplogroup, rather than in the family haplotype.

MLE -- The Most Likely Estimate of when the MRCA between two people lived.

Modal -- The value at which an absolute or maximum occurs in the frequency distribution of the variant.

MRCA -- The Most Recent Common Ancestor between two people. See the expanded definition at the bottom.

Mutation -- Small changes during the DNA copying process during transfer from father to son.

STR -- Short Tandem Repeats = A VNTR (see below) in which the repeated sequence is from one (1) to five (5) base pairs.

Y-chromosome -- is passed down from generation to generation only through the male line;  from father to son, father to son, etc.

VNTR -- Variable Number Tandem Repeats.  A defined region of DNA containing multiple copies of short sequences of bases, which are repeated a number of times, the number of repeats varying among individuals in the population.

Most Recent Common Ancestor (MRCA)

Click here to go to a site that helps you calculate your MRCA for two related families.

Click here to see a diagram of the MRCA prediction of various numbers of test markers.

In order to understand MRCA, you must understand the following:
MRCA: (most recent common ancestor): the common ancestor between two people.
MLE: most likely estimate of when the most recent common ancestor between two people lived. It appears that testing labs are using a probability of 50% when figuring the MLE rather than a higher percentage such as 90%.
Generation: Genetics uses 20 years for each generation.
Heyer principle: Y chromosome mutations occur generally once every 500 generations per locus (or "per marker") with a mutation rate of 0.2%.
Example of Heyer principle: Using the Heyer principle, we would expect EACH locus to change 1 digit in 500 generations. If we use a 12 marker test, in 500 (generations) / 12 (markers) = 41.667 generations we would expect to have a change in 1 of the 12 markers by one digit. Thus, two Jordans with a common ancestor would almost certainly have a one digit change in 835 years or have a one digit difference in their marker results.

As genealogists, we want to know when the MRCA between two people lived. We know that where all 12 markers match, there is a 50% probability that the MRCA was no longer than 14.4 generations (288 years), and a 90% probability that the MRCA was within the last 48 generations. The Most Likely Estimate (MLE) for a 12/12 match, however, is 14.4 generations (which happens to be the 50% probability figure; 48 at 90%, 63 generations at 95%). The range for a 12/12 match is 1 to 63 generations.

What if there is an 11/12 marker match? For an 11/12 match, there is a 50% probability that the MRCA lived no longer than 36 generations, which is also the MLE. This translates into 36 x 20 = 720 years. The range for an 11/12 match is 1 to 104 generations (85 generations at 90%, 104 at 95%).

What if there is a 10/12 match? For a 10/12 match, there is a 50% probability that the MRCA lived no longer than 61 generations, which is also the MLE. This translates into 61 x 20 = 1220 years. The range for a 10/12 match is 1 to 145 generations (122 at 90%, 145 at 95% probability).

We do know that if the results of two people are different by one mutation, that these people are related. If different by two mutations, probably related. As we see three or more mutations, the people who may be related are very distantly related. The concept of MRCA puts the relation back many generations.