Most of us are familiar with the terms genetics, DNA, chromosomes and genes. Genetic genealogy has its own set of terms, some of which are specific to the field of genetic genealogy/ancestral DNA testing (haplogroup, haplotype, clade, subclade, founder population, genetic origin, HRV, etc.) and others that are common to most genetic fields (markers, mutations, segments, blocks, SNPs, STRs, alleles, phenotype, genotype, etc.)
Terminology may vary slightly depending on which company you test with: i.e. 23andme.com refers to matching relatives as DNA relatives.
Here are some of the more common important genealogy terms, most of which have to do with genetic genealogy testing.
Allele – a variant of a given gene.
Autosomal DNA – genes that determine hereditary conditions, physical features and family relations. Think of autosomal dominant and autosomal recessive – in my family, blue eyes an autosomal recessive gene. I have brown eyes and so do my parents. My brother has blue eyes, as did our paternal grandfather and maternal grandmother. Relative matching is done with autosomal DNA.
Block or segment (of DNA) – Continuous segments on a chromosome measured in centiMorgans. When comparing the DNA of two people, anything matching above 5 consecutive centiMorgans on a chromosome is significant and means that the two individuals are somehow related. Ex.: The longest block on chromosome 17 for two related individuals is 10 centiMorgans.
centiMorgan (cM) – a unit of measuring genetic distance on a chromosome. For example, siblings share up to 50% DNA. My brother and I share 46% DNA or 2,527 centiMorgans. Most of our matching relatives, who appear as anywhere from 2nd to remote cousins, share less than 200 cMs with my brother and I, therefore less than 2% DNA.
Founder/founding population – Also known as Founder Effect. “In population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population.” (Wikipedia). For example, K originated in the Middle East thousands of years ago, but its splinter clade k1a1b1a is more European and specific to Ashkenazi Jews, having established itself up to 2,000 years ago in the Rhine basin. This subclade is believed to have originated from one woman nicknamed “Katherine”.
GEDCOM – Stands for Genealogical Data Communication. A type of file in which user-entered genealogical data is stored and can be exchanged. Family Tree Builder by MyHeritage is one of the most popular GEDCOM software.
Genetic drift – A mechanism of evolution. Best explanation given here: http://evolution.berkeley.edu/evolibrary/article/evo_24
Genetic origin – Basically, where your ancestors come from over a given time period, which is expressed as a haplotype.
Genotype – genetic material that is used to determine ancestry.
Haplogroup – A haplogroup and its branches or subclades is often mapped out in a haplogroup tree.
Haplotype – genetic markers that make up a haplogroup. Sometimes haplotype is confused for haplogroup and used interchangeably.
Markers – A specific point on a chromosome, usually the cause of a gene variant or mutation. Markers are used in determining inherited conditions, including ancestry and disease.
Maternal line – Your mother’s mother’s mother and so on. Based on mitochondrial DNA.
Migration – When people move from one place to another and settle there permanently, either individually or in groups. Plays a role in evolution along with natural selection, mutation and genetic drift.
Mitochondrial DNA – The X-chromosome is surrounded by a sac-like bacteria that determines the maternal line haplogroup and its genetic origin in both men and women. Passed from mother to child. Unlike Y-DNA, mitochondrial DNA can mutate slightly.
Modal haplotype – A more specific haplotype to determine specific lineages (Cohen, Levite, etc.).
Mutation – A permanent alteration on any part of a gene.
Paternal line – Your father’s father’s father and so on. Often the same paternal surname is passed down through generations.
Phenotype – genetic material that is used, along with environmental factors, to determine certain physical and behavioral characteristics. Also see: https://www.23andme.com/en-ca/gen101/phenotype/
Relative matching –Comparing the DNA (mostly autosomal) of two or more people to find matching markers and gene sequences that prove relation. Here is a good article explaining how FTDNA’s Family Finder works: https://dna.land/relative-finder-info
SNPs – Single-nucleotide polymorphism. Markers that are used to determine Y chromosome haplogroups and subclades, as well as the subclade of the mitochondrial X chromosome DNA. More about SNPs here https://www.23andme.com/en-ca/gen101/snps/
STRs – Short Tandem Repeats. Markers that are used to determine Y chromosome haplogroups, as well as Y modal haplogroups (Cohen).
Subclade – A subgroup or branch of a haplogroup. Ex. J1 is a subclade of J. Sometimes subclade and haplogroup/haplotype are used interchangeably (think of clade as a new haplogroup).
Vital records – a birth, marriage or death record or certificate.
X-match(ing) – This mostly applies to ftdna.com and gedmatch.com. When two people have matching segments on their X chromosome, meaning they are related through their mother’s maternal line or their father’s maternal line, or both. It works like this:
- If two women are an X-match, they can be related through either their mother’s or father’s maternal line, or even both. It is difficult to tell which, though.
- If a man and a woman are an X-match, they could either be related through their mother’s maternal line, or the woman can match the man through her father’s maternal line, but not vice versa.
- If two men are an X-match, then they can only be related to each other through their mother’s maternal line.
Please note that two individuals who are an X-match can also be related through autosomal DNA, and are likely closer in relation that way.
Finally, when you match someone on the X-chromosome, you do not necessarily need to share the same maternal-line haplogroup.
For further reference: