This document defines key DNA and genetic genealogy terminology used in autosomal DNA testing and analysis. It explains terms like alleles, centiMorgans, haplogroups, haplotypes, identical by descent, inbreeding, phasing, single nucleotide polymorphisms, and more. Understanding these concepts is important for interpreting autosomal DNA test results and determining genetic relationships between individuals and ancestral populations.
2. Admixture
The autosomal DNA test ethnicity estimates.
Alleles
“An allele is one of a pair of genes that appear at a particular
location on a particular chromosome and control the same
characteristic, such as blood type or colorblindness.”
Vocabulary.com
Below you can see I inherited the Allele C from each parent.
The two together are a genotype. My genotypes here are
good. Sometimes they cause disease.
3. centiMorgan (cM)
“A centiMorgan (cM) is a measurement of how likely a segment of DNA is
to recombine from one generation to the next. A single centiMorgan is
considered equivalent to a 1% (1/100) chance that a segment of DNA will
crossover or recombine within one generation.” Family Tree DNA
4.
DNA Segment
“A DNA segment is any continuous run or length of DNA. It is described by
the place where it starts and the place where it stops.” From Family Tree
DNA.
Endogamous
“An endogamous population is one where the members usually only marry
within the population group. The bases for endogamy may be geography,
ethnic identity, social class, or religion. Long periods of intermarriage have
left many endogamous populations with lower than average levels of
genetic diversity. Examples of historically endogamous populations are the
Amish, the Basque, and the various sub-populations of the Jewish
Diaspora.” From Family Tree DNA
5. Fully Identical Segment
“Two individuals are said to share a fully identical region (FIR) or completely
identical region of DNA if the alleles on both chromosomes are identical
throughout the region…” Siblings share fully identical regions because they
can inherit DNA in the same region from both parents.
The Green in the chart about shows fully identical regions of siblings
6.
Haplogroup
“A haplogroup is a major branch on either the maternal or paternal tree of
humankind. Haplogroups are associated with early human migrations. Today
these can associated with a geographic region or regions.” From Family Tree
DNA
Haplotype
“A haplotype is the set of values for a set of DNA values. For example, the
results of the Y-DNA12 test for one person is their haplotype.
Two individuals that match exactly on all markers have the same haplotype.”
From Family Tree DNA
AncestryDNA uses Haplotypes to phase their results or separate them
according to maternal and paternal sides.
7. Half-Identical Region (HIR)
“A half-identical region (HIR) is when two people share a DNA segment
that’s half matches. The half-identical region may be either identical by
descent (IBD) or identical by state (IBS).” From Family Tree DNA site
We receive half of our DNA from our mother or father. Our matches will
match on our maternal or paternal side and will share half identical DNA.
8.
Identical by Descent (IBD)
Means a segment is inherited from a common ancestor
Identical by State (IBS)
Means a segment can’t be attributed to a common ancestor. Could be a
coincidence or an ancient segment.
9.
Inbreed
“In genetics, inbreed refers to someone whose parents are related. It most often
refers to cases where the relationship is within five generations.” Family Tree DnA
New Ancestor Discoveries NAD
You might hear AncestryDNA testers referring to NAD’s. They are talking about the
“New Ancestor Discoveries” you find on your DNA home page. I’ve found these are
generally not ancestors. They generally point to cousins.
10. DNA Segment mapping
Using autosomal segment data provided by companies like 23andMe and
Family Tree DNA to create a map of all your shared segments. Kitty’s DNA
Mapper website allows you to create maps with segment data from any
source.
12. Triangulation
Is when 3 or more people match on the same segment. This is where the
chromosome mapping, and chromosome browsers at 23andMe and Family
Tree DNA come in handy.
13. Single Nucleotide Polymorphism SNP’s
DNA copying errors. The more SNP’s we share the more closely related we are.
Below you can see a sequence that repeats until a copy error occurs, and we
get a G instead of a C.
A A T C G T
A A T C G T
A A T C G T
A A T G G T
