A short list of terms that we use and what they mean
DNA Di-oxy-ribonucleic acid, the fundamental biochemical building block of life,
which has a double-helix chemical structure. All living things have DNA in
all their cells. The two kinds of DNA typically tested for genetic
genealogy are from the male Y chromosome and mitochondria (abbreviated,
mtDNA) in every cell of both sexes. A third term, "autosomal", refers to all
types of DNA except those of the X & Y chromosomes.
Match A comparison of two Y-DNA samples which show great resemblance
to each other. They may be identical or display only a small number of minor
Match Quality A quantification of the degree of matching, i.e., the similarity of two
compared haplotypes. Several methods are used:
The preferred method is as a mutation-rate-adjusted probability of a
common ancestor in a specified number of generations, e.g., 90% within
A less-preferred method is "genetic distance" (GD), in which
the absolute differences of all allele values are summed. When used, the
number of markers compared should always be stated, e.g., 2:37.
As a fraction, with the number of markers whose alleles
agree completely (or disagree) as the numerator and the number tested in common as the
denominator e.g, 36/37 (or 1/37).
The degree of dissimilarity between two compared haplotypes, often
expressed as a percentage. This is essentially
the obverse of the first method.
CMA Common male ancestor, a direct paternal ancestor shared by two or more men
with matching Y-DNA.
MRCA Most recent common ancestor. The most recent common
ancestor is important because, if two persons share one ancestor, they will
also share the preceding ancestors.
MDKA, EKA Most distant (earliest) known ancestor, either paternal or
maternal. Taylor Family Genes asks for
this information because it helps "zero in" on the MRCA.
TMRCA Time to most recent common ancestor, expressed in
generations. Technically, the TMRCA is in "transmission events"
(number of generations minus 1). A transmission event occurs when a man
fathers a son.
A paternal lineage consisting of the patriarchal founder and his direct
filial descendants. In practice, only living descendants are found though
DYS Names a specific place (technically, "locus") on the Y-chromosome for STR testing,
also "marker". A typical marker name is "DYS393".
Marker This word has two meanings in DNA:
(1) For STR testing, it means a locus (place) on the Y-chromosome, with a name like
(2) For SNP testing, it means a specific, identified & catalogued mutation characterizing a
particular haplogroup, with a name like "P297".
Because of its dual meaning, it is good to identify the context in which one
uses the term.
Alleles In STR testing, The number of counted repetitions of DNA
patterns for a particular locus.
STRAbbreviation for "Short Tandem Repeats". In this type of
testing, repeating DNA patterns are counted and the values reported as
integers. With sufficient markers tested, STR testing specifically identifies an
individual haplotype and an ancestral paternal line. It can predict the
haplogroup into which the haplotype falls.
SNP Abbreviation for "Single Nucleotide Polymorphism". In this
type of testing, specific previously-catalogued mutations of DNA are looked for &
reported. SNP testing definitively establishes a haplogroup.
Haplogroup A category of types of DNA with similar
characteristics, a group of haplotypes. A common ancestor for all within a
haplogroup is most likely in the very distant past.
Haplotype A specific & unique pattern of Y-DNA. When two men
have the same haplotype, they have a common paternal ancestor, probably
within a genealogical time frame.
Mutation A change in the DNA pattern during transmission from father to son. Mutations
happen infrequently -- on the order of once in every 250 to 400 generations
-- and (it's believed) randomly. In STR testing, a mutation is revealed by a
difference in allele values. SNP testing looks for specific, known
Genetic Distance A measure of the difference between two haplotypes. A common technique
is to sum the absolute differences of all alleles across all loci.
Genealogical Time Frame The period of time for which it is possible to
identify specific individuals as one's ancestors. The length of this period
varies with place and culture; it is dependent on written records, use of
surnames and other factors. For western Europe, the consensus estimate is
that the genealogical time frame extends from the mid-1300s to the present.
Also see this page.