Learning the DNA Lingo
Participating in a DNA surname project? We’ll help you understand some of the scientific terms you'll come across.
Surname project participants may be overwhelmed by the terms genetic genealogists and testing companies toss around. We’ll help you understand some of that confusing lingo.

DYS (DNA Y-chromosome Segment): DYS followed by a number identifies a short segment of Y-chromosome DNA, also called a Short Tandem Repeat (STR) or a marker. A Y-DNA test reveals how many repeats of a particular nucleotide sequence are found at that DYS marker. For example, DYS390 is one of the most commonly tested Y-DNA markers, and values for the marker typically range from 19 to 28 repeats.

Haplogroup: a collection of related haplotypes with a common ancestor. The haplogroup (also called a clade) is usually defined by a single nucleotide polymorphism (SNP) mutation that arose in an ancestor hundreds or thousands of years ago, and is found in all of the descendant haplotypes.

Haplotype: an individual’s set of single nucleotide polymorphisms (SNPs) or DYS markers. Males who are recently related through their paternal line will have similar haplotypes and belong to the same haplogroup. The more diverse two haplotypes are, the more time has passed since their most recent common ancestor.

Modal: the set of most-common DYS values in a group of closely related haplotypes. A particular branch of a surname, for example, might have a slightly different modal from another branch of the name.

MRCA (Most Recent Common Ancestor): the most recent paternal ancestor of two males. Every male on earth shares an MRCA with every other male, although some will have an MRCA thousands of years ago and others will have an MRCA within the last few generations. Y-DNA results can reveal how many generations have passed between two participants and their MRCA.

Mutation: a usually harmless change in the DNA sequence. A mutation can change the value of a DYS marker, for example. Although mutations are random, they typically occur at a known rate and thus provide a rough molecular “clock” useful for surname studies.

NPE (non-paternal event): a break in the Y-chromosome line resulting from adoption, infidelity or another cause. NPEs (also known as non-paternity events or false paternity) can be detected by Y-DNA testing.

SNP (Single Nucleotide Polymorphism): the mutation of a single nucleotide in the Y-DNA sequence. One of the nucleotides, represented by the letters A, T, C or G, replaces another at that location in the sequence. Haplogroups are defined by SNPs.

STR (Short Tandem Repeat): a repeat of a short nucleotide sequence on the Y-chromosome. The DYS390 marker, for example, is an STR with between 19 and 28 repeats of the short nucleotide sequence. Closely related males will have a similar number of repeats.

TMRCA (Time to Most Recent Common Ancestor): an estimate of the amount of time between two males and their most recent paternal ancestor, calculated using differences between the two haplotypes.
Thinking about incorporating genetic genealogy into your family history research? Start with our complete guide to genetic genealogy, part of the December 2009 Family Tree Magazine.
From the September 2010 Family Tree Magazine
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