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DNA Glossary for Genealogists

Last updated: 2011 Nov 10

allele
variant of a gene or genetic marker. For STR markers, each allele is designated by the number of repeats of the short base sequence.
autosome
one of the non-sex-determining chromosomes. Autosomes occur in nearly identical pairs. See also X and Y.
base
the building block of DNA, one of four molecules that link up to make a DNA chain. The four are named adenine, cytosine, guanine, and thymine (A, C, G, T for short). These are also called nucleotides.
buccal
pertaining to the cheeks or the mouth cavity in general. Buccal cell samples for analysis can be obtained easily and painlessly by a gentle brushing or scraping of the inside of the mouth.
chromosome
one of the DNA macromolecules found in the cell nucleus. Humans have 46 chromosomes. See also X and Y.
CRS
the Cambridge Reference Sequence for mtDNA, used for convenience to compare with all human mtDNA sequences, such that any sequence can be expressed concisely as a relatively short list of difference from the reference
DNA
deoxyribonucleic acid. The chemical constituent of genes and chromosomes. DNA has four different base units, designated A, C, G, and T, which are connected in long double chains, and the sequence of these bases encodes the genetic information.
DYS
DNA Y-chromosome Segment. A label for loci or genetic markers on the Y chromosome. Each marker is designated by a number, according to international conventions. Virtually all DYS designations discussed in the context of genetic genealogy are those of STR markers (which are useful for genealogy because of their relatively high mutation rate).
electropherogram
the record produced by the analytic technique called electrophoresis, which segregates complex molecules in a mixture by applying an electric field. The molecules migrate at different rates, according to molecular weight. In the case of DNA analysis, this determination of molecular weights is equivalent to measuring the length of each DNA segment in a batch, as well as the relative amount (subject to issues of calibration) of each type of DNA segment.
gene
a meaningful sub-unit of DNA, encoding a protein.
gene conversion
a process replacing one allele of a pair with a copy of the other. This term is used by extension for all kinds of loci, not just genes. See also recLOH.
genome
the entire inventory of nuclear DNA in an organism.
genotype
a set of allele values of one or more markers for one individual. Since most of the DNA consists of nearly identical pairs of chromosomes, a genotype typically has two alleles for each marker, one from each parent. See also haplotype.
haplogroup
a classification comprising many different haplotypes thought to be related. Haplogroups are defined in terms of markers that mutate so slowly they are treated as if they have occurred only once in all time. The major haplogroups originated thousands or tens of thousands of years ago.
haplotype
a set of allele values of one or more markers for one individual and identified as coming just from one parent, particularly markers on the Y chromosome or in mitochondrial DNA. See also genotype.
heterozygous
having two different alleles in the two copies of the same marker or locus existing on a pair of chromosomes. By extension, this term is sometimes applied to the two copies of a locus found on opposite arms of a palindrome on the Y chromosome. See also homozygous.
homozygous
having the same allele in the two copies of the same marker or locus existing on a pair of chromosomes. By extension, this term is sometimes applied to the two copies of a locus found on opposite arms of a palindrome on the Y chromosome. See also heterozygous.
HVR1
Hypervariable Region 1. A portion of the mtDNA molecule noted for its especially high mutation rate, consisting roughly of locations 16024-16569.
HVR2
Hypervariable Region 2. (See HVR1.) The limits of HVR2 are even more vague than for HVR1. HVR2 is generally said to start at location 1 and to extend for a few hundred bases, but part of this region is often called HVR3.
locus
(plural: loci) specific site on a DNA chain.
marker
a distinctive sub-unit of DNA, often not part of a gene. Often used interchangeably with locus, but referring to the contents of the site, rather than the site itself.
microsatellite
See STR.
mitochondria
organelles within the cell responsible for converting food into usable energy. Each mitochondrion has its own DNA. The mitochondria in a child come entirely from the mother, and so mitochondrial DNA ("mtDNA" for short) is a tracer of female-line ancestry, just as Y DNA is a tracer for male-line ancestry.
motif
a sequence of DNA bases (typically three or four) that is repeated in multiple copies in a microsatellite or STR. The term is also used for a combination of several mutations associated with a particular haplogroup, especially for mitochondrial DNA.
mtDNA
See mitochondria.
mutation
An event in which the DNA chain alters. In the case of STR markers, a mutation is almost invariably the gain or loss of one repeat of the basic short sequence (or, rarely, two repeats). Other types of mutations include the substitution of one base for another and the insertion or deletion of a whole segment. See also recombination.
nucleotide
a unit of DNA. See also base.
organelle
any small, compact, and cohesive entity within a cell. An organelle is to a cell what an organ is to a multi-celled creature.
palindrome
a sequence of letters (or DNA bases) that reads the same forwards and backwards.
PCR
Polymerase Chain Reaction. A chemical process that replicates a given sample of DNA many times, in imitation of natural replication. The process cycles between two stages: splitting the two strands of DNA apart and then forming new double strands by adding a mixture of the enzyme polymerase and the four DNA bases. By adding primers as well, the process can be used to replicate just the one or more DNA segments of interest.
poly-C
consisting of many contiguous cytosine ("C") bases. Such segments of DNA are prone to mutation by the insertion (or sometimes the deletion) of one or more cytosines, presumably by the same process that produces ordinary STR mutations.
primer
a reagent consisting of a relatively short DNA sequence exactly matching the sequence flanking a marker of interest. A primer needs to be long enough that (in principle) it matches only one spot in the entire human genome, but, in practice, many segments of human DNA appear more than once, through a poorly understood process of duplication. Two primers, one for each end of the desired marker, are used in the PCR amplification step to selectively amplify that marker. The primers are often tagged with a flourescent dye to help in detecting the amplified DNA segments.
recLOH
recombinant loss of heterozygosity. See also gene conversion.
recombination
a process of "mixing and matching" of paired chromosomes that takes place at cell division. One or more segments may be swapped between the two chromosomes, or occasionally a segment may replace the corresponding segment on the other chromosome. This process can also occur on palindromic segments of the Y chromosome and may affect paired loci, such as DYS385a and DYS385b.
STR
Short Tandem Repeat. Also known as microsatellite. This is a genetic marker consisting of multiple copies of a short motif, (a sequence of DNA bases). Occasionally, a microsatellite will mutate by the gain or loss of one repeat. So-called "simple" STRs have just one contiguous set of repeats; "complex" STRs may have multiple sets of repeats separated by short patches of non-repeating DNA and may even have repeats of more than one motif.
umbilical
in genealogy, referring to the straight maternal line of ancestry (child to mother to mother's mother to mother's mother's mother and so on)
X
one of the two sex-determining chromosomes, See also Y.
Y
one of the two sex-determining chromosomes. A person with the combination XX is female, while a person with XY is male. Most of the Y chromosome, unlike the others, does not trade DNA with a "partner chromosome," and it therefore passes essentially intact from father to son. This property leads to a minimum of ambiguity in interpreting the results of Y DNA analysis.
 

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