Basic
Genealogy DNA Definitions
Allele
Any one of a number of genetic markers that can exist in a particular location on a chromosome. In genealogy, an allele is most often used to
refer to the number of the pattern of repeats in a given DNA sequence. The variation in the number of these repeats may be used to differentiate
people.
DYS (DNA Y-Chromosome Segment)
The number given to a designated marker on the Y-Chromosome. DYS numbers are controlled by the HUGO Gene Nomenclature Committee to maintain
uniformity in the system. For example: DYS393 = 12 DYS393 is the number system controlled by HUGO, 12 is the allele (also called the number of repeats).
Gene
Among their other functions genes control heredity. Genes are the fundamental unit of heredity, they are a specific unit of DNA within a
chromosome.
Genome
All the genetic material (DNA) in a cell. The full set of chromosomes carried by a particular organism.
Haplotype
The genetic make-up of an individual chromosome. In genealogy testing, a
Y-chromosome haplotype is the numbered results of a Y-DNA test. These numeric test results are then compared to other individuals haplotypes for
indications of relationship. The female mtDNA test results are reported as differences form the Cambridge Reference Sequence. In its most simple form;
your haplotype is the complete set of results on whatever markers were tested.
Haplogroup
A large group of people who share the same unique event polymorphism (changes) at a specific location in their DNA sequence. Haplogroups are used
to define genetic populations, and are of particular interest in genealogy as the members of the group are thought to share a common founding ancestor. Y-DNA haplogroups are assigned lettered A - R designations, and are then
further subdivided with numeric and lower case letters. MtDNA haplogroups have been assigned different lettered and numeric designations.
Locus
The specific location on a chromosome or location where a particular marker
is located.
Marker
A distinctive physical location on a segment of DNA with no known coding
information. However, it is a sequence of DNA with a known genetic pattern that can be tested for a pattern of inherited characteristics. In a
genealogy Y-DNA test DYS393 is the name of a marker.
Mutation
A change in the DNA sequence. These are inheritable changes in non-coding
areas of the DNA sequence used as markers in genealogy to determine whether individuals share a common ancestor.
Non-Coding Regions
Segments of DNA with no known purpose, however acts as a recorder accumulating mutations and preserving ancestral history. Also know as "junk
DNA."
SNP (Single Nucleotide Polymorphisms) (Snip)
A small change in the DNA sequence when a single nucleotide, such as when a
base A replaces becomes a C, G or T. When this change occurs it is called a polymorphism. These changes occur infrequently, and so are used to define
haplogroups.
STR (Short Tandem Repeats)
Short patterns in the DNA sequence which repeat a number of times in a row.
For example GATAGATAGATAGATA, four repeats of the GATA sequence. In this example the allele or marker has a numeric value 5. In Y-DNA testing the
differences in STR repeats provide the basis for comparison among individuals
STR vs. SNP
DNA testing for genealogy usually starts with STR testing from between 12
and 37 individual markers. The test results are then studied to determine the haplogroup for the individual being tested. Occasionally the individual
may be difficult to place in a haplogroup or he may simply wish to further refine his test results, SNP testing may then be ordered.
UEP (Unique Event Polymorphism)
A type of mutation in which the rate of change is so low that it can be
called a one time event. This essentially unique mutation is useful for studying deep ancestry. SNP's are in this class of mutations.
MORE TO READ
This is an excellent site on DNA 101 lessons: http://blairgenealogy.com/dna/dna101.html
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