This brief glossary was written to support an article about the Y
chromosome; this, rather than define every term in the article itself. It's
presently restricted to a handful of Y-DNA terms, but will grow in the
future. See below for acronyms EKA, STR,
SNP, LCA, MRCA, NPE, and Y-DNA.
- Autosomes. Autosomal testing sequences the first 22 pairs of
chromosomes in the human genome. They are formed in the parents' gamete
cells through recombination. The X and Y chromosomes, the 23rd pair, are
not significantly involved in recombination.
- Base Pairs. We inherit half our DNA from each
parent. Each set is a recombination -- chromosome by chromosome -- of
half of their parents' DNA. In this way, it can be said that we have
two genomes, one from the mother and one from the father. However, the Y
chromosome has only a set of single bases, that from the father's Y. I's
inherited whole hog, not just a half.
- Big Y. Sometimes abbreviated to BY, the Big Y is an FTDNA product
that tests up to fifteen million nucleotide positions on the Y chromosome.
The latest iteration is called Y-700. In addition to thousands of SNPs, it
includes up to 700 STRs. To date, it's the most effective and affordable
way to find previously undiscovered mutations on the Y.
- Downstream. To move downstream a tree (i.e., a "downstream SNP")
takes your X degrees closer toward the living branches of a tree. This is
analogous to looking at your genealogy tree from your own entry downstream
toward your children, grandchildren, and great grandchildren.
- Earliest Known Ancestor (EKA). An EKA is the earliest proven
ancestor known in a lineage, most commonly seen in paternal and maternal
lineages. For example, the EKA of my fatherline is John Cooley, c1738-1811.
The EKA of my motherline is Ruth Ruema Hoover, 1825-1905.
- Haplogroup. A set of SNP markers assigned to a specific ancestor
(who is usually unidentified). They're presense and placement is inferred
through multiple testing. In other words, they are SNPs grouped together at
the node of a tree. The number of member markers can change as new
haplogroups emerge through additional testing. For example, in Cooley Group
CF02, haplgroup R1b-A12020, SNP testing has revealed an unknown MRCA for the
Goshen, New York Cooleys. Although they are of the same haplogroup, these
testers have neither the Benjamin Cooley nor Samuell Coley SNPs, and belong
in a subgroup all their own. R1b-A12020, yes, but subclade R1b-A20349 as
well. Such designations are found in Y chromosomal and mitochondrial
lineages. Autosomal values shift dramatically from one generation to the
next and defy haplogroup designations.
- Haplotype. A set of markers inherited from one of the parents.
The term is most often used in genetic genealogy to refer to a male's
specific Short Tandem Repeat results. Each line on the results page of the
Cooley DNA Project represents a tester's haplotype.
- Last Common Ancestor (LCA). See Most Recent Common Ancestor (MRCA).
- Marker. Any number of forms of genetic mutations, including SNPs
and STRs, are referred to as genetic markers. Insertions and deletions are
also common markers. Markers can be significant to health. However,
genetic genealogy generally avoids such markers as they are influenced by
- Most Recent Common Ancestor (MRCA). The common ancestor to all
descendant branches; for example, a great-grandparent common to all second
cousins in the tree.
- Non-Paternal Event (NPE). An NPE results from adoption or an
extramarital affair. The child often gains the mother's maiden name or the
adopted father's surname. NPEs are often found through autosomal testing,
but can also be commonly found in Y-DNA testing, even if several generations
- Nucleotide. A simple molecule that represents a single base in a
genome. Each base is comprised of one of four molecules: adenine (A),
cytosine (C), guanine (G), and thymine (T), which gives rise to the genetic
alphabet soup, ACGT. The human genome has about 3.1 billion base pairs.
- Short Tandem Repeats (STRs). These are just what they sound like:
short strings of bases that repeat the same sequence near, or
in tandem of, one another. For example, I have 34 repeats of TTTC at
the region called DYS449. All other members of Cooley group CF01, including
my father, has 33 repeats. I'm proud to call myself a mutant.
- Single Nucleotide Polymorphism (SNP). A mutation caused by a
nucleotide flipping to one of the other four genetic letters.
- Upstream. Moving up a tree (i.e., an "upstream SNP"), closer to
the ancestral source. A grandfather is upstream of his grandchildren.
- Y chromosome (Y-DNA). One of the 23rd pair of
chromosomes. A female receives an X from both parents; a male gets an X
from his mother and Y from his father. In other words, it passes down only
the fatherline. Women are not part of the inheritance pattern. (Consider
that the male sex gene, SRY, cannot possibly be inherited in any other way.
It lives on the Y.)