In an effort to better explain the complex dynamics of DNA, SMGF created the following animations as an introduction to the field of molecular genealogy. Whether you are interested in learning for yourself, a friend, or a student, we hope these animations will introduce a new foundation of the growing field of molecular genealogy.
Introduction to Molecular Genealogy
Four Types of DNA
Y Chromosome DNA
Mutation and Haplotype
These are common terms that are used in molecular genealogy.
One of the possible values for a marker or a gene. For instance, with Y chromosome DNA, the values of “13” or “14” would be different alleles for DYS393.
The type of DNA that is inherited from both parents. Autosomal DNA controls physical characteristics, such as eye color or facial traits.
A change in a descendant marker value back to its ancestral value.
One of four basic components of DNA: A is for Adenine, G is for Guanine , C is for Cytosine, and T is for Thymine.
A point in the development of a population when the numbers of individuals were greatly reduced. For instance, a family might be reduced to only a few members at one point in time.
A physical structure consisting of DNA and supporting proteins. Human cells normally contain 23 pairs of chromosomes (or 46 total). 22 pairs are called the autosomal chromosomes, and the 23rd pair includes the sex chromosomes (an X chromosome and a Y chromosome).
An evolutionary family tree that shows relationships over time between individuals.
With Y chromosome DNA, this is the time back to a common ancestor for two or more lineages.
The region of the DNA molecule that contains specific instructions for creating proteins.
A set of markers used to uniquely identify an individual, often for legal purposes. These are different markers than the ones used in Y chromosome or mtDNA testing.
An ancestor that two people have in common. For instance, first cousins all share a common grandfather, who would be a common ancestor. For Y-DNA comparisons, a common ancestor refers to a common paternal-line ancestor.
Similarity in DNA marker values when there is no actual genetic connection.
Loss of a segment of DNA, which may be as small as a single base, or large enough to encompass one or more genes.
DeoxyriboNucleic Acid. A complex molecule found in cells that contains the genetic instructions necessary for life.
The laboratory process of separating DNA out from a sample (as contained in a mouth wash, cheek swab, blood, or other body fluids).
The analysis of DNA for purposes of identification.
The basic shape of the DNA molecule, with two strands that twist around each other in a helical fashion. Think of a strand of DNA as like a ladder, with the rungs of the ladder represented by base pairs.
DNA markers (such as DYS385, DYS459, and YCAII) where duplicated genetic material results in two values from different locations on the Y chromosome. For duplicate markers, it is possible to determine the two values, but not the physical location of each value. Results are given in ascending order. For example, marker DYS385 may have a value of 11 and 14, but it is not possible to know if the order is 11-14 or 14-11. This prevents an accurate direct comparison of duplicated marker values between two individuals and complicates the determination of Time to Most Recent Common Ancestor.
A designator for Y-chromosome markers. DYS stands for ‘DNA Y-Chromosome Segment’.
A graphical display of the raw DNA marker data produced by automated DNA analyzers.
The practice of marrying within a social group. Endogamous societies have a high number of first and second cousin marriages.
forensic DNA testing
DNA testing that is used as legal evidence. Forensic DNA testing typically uses CODIS markers that are not used for Y-DNA or mtDNA testing.
The effect on a specific population due to the genes or marker values of a single individual (founder).
Pronounced “jed-com”. An abbreviation for “Genealogical Data Communications”. A standard file format for genealogy records.
The basic unit of heredity, consisting of a segment of DNA that produces a specific characteristic or function. Genes contain the instructions for the production of proteins, which make up the structure of cells and direct their activities.
A measure of the spread in values for a genetic marker. Greater gene diversity correlates with marker mutation rate, but is also affected by underlying structure within a population (caused by founder effect, etc).
The total difference in genetic marker values between two individuals. In general, the greater the genetic distance, the earlier two individuals shared a common ancestor.
A collection of information about a person’s genes or marker values.
The complete package of genetic material for a living organism, organized in chromosomes. A copy of the genome is found in most cells.
The study of the genome.
All the allele values for a specified set of DNA markers. Note that mtDNA and Y-DNA genotypes are generally called haplotypes.
The process of determining and confirming genetic marker values.
The cells of the body involved in reproduction. Sperm of the male and eggs of the female are formed from germ cells.
Population groups that share common Single Nucleotide Polymorphisms (SNPs). Haplogroups are useful for defining populations, but have limited application in genealogy research. Since SMGF is mainly concerned with the application of DNA testing in genealogy, we do not display haplogroups along with haplotypes.
A set of Y chromosome DNA results or mitochondrial DNA results.
The passing down of traits from parents to their children. The process of heredity occurs through the genes.
An individual who has inherited two different alleles at a particular location.
An individual who has inherited identical alleles at a particular location.
infinite alleles mutation model
This model assumes that mutations can occur in any number of steps. For instance, if two cousins differ by DYS390=12 and DYS390=14, then we assume a single mutation of two allele values has occured.
Agreement to take part in a study that is given voluntarily and based on an understanding of the risks and benefits of the work.
A mutation in which a segment of DNA is inserted into another segment of DNA.
DNA that does not have any apparent biological trait or function. It is possible that so-called “junk” DNA may have purposes that have not been determined.
A specific location on a DNA molecule. Also called a genetic marker. The plural is “loci”.
A reference to a specific location on a DNA molecule. Also called a locus
The number of marker values in common E.g. a match of 35/36 means two individuals have 35 out of 36 marker values in common. In general, the closer the match, the closer two individuals will be related.
Another term for “STR” – A repeat of genetic material at a specific location.
An STR value that contains a partial repeat, e.g. 17.2 for DYS458.
Movement of a population from one area to another.
Abbreviated mtDNA (pronounced em-tee-D-N-A). A type of DNA that is found in small bodies within cells called mitochondria. Both women and men have mtDNA, but only mothers pass on their mtDNA to the next generation.
A group of atoms that forms the smallest particle of any substance.
The most recent ancestor that two individuals have in common. For example, first cousins share a grandfather, and second cousins share a great-grandfather. When comparing Y chromosome DNA results, the Most Recent Common Ancestor (MCRA) refers to the direct paternal ancestor for each person. When comparing mitochondrial DNA results, the Most Recent Common Ancestor (MCRA) refers to the direct maternal ancestor for each person.
A change or variation in a gene or a genetic marker.
DNA that does not appear to be tied to any biological trait or function.
A primary component of DNA comprising a base (A, G, C, T) and supporting phosphate and sugar molecules.
The absence of a gene or marker value at a specific location. A null allele may be caused by a deletion of genetic material or the inability to detect a true marker value due to the testing process.
paternity DNA testing
DNA testing that is used to establish the identity of a father. Paternity testing uses different markers than are used for Y-DNA or mt-DNA testing.
A family name derived from name of the father or a paternal ancestor. Examples include Johnson (John’s son), MacDonald, O’Leary, and Ivanovich.
(Polymerase Chain Reaction): The amplification of DNA segments. An important step in the process of determining DNA marker values.
A standard form for entering genealogical information, including the names, dates of birth, dates of marriage, and dates of death of ancestors.
The visible characteristics of an individual that are attributed to genes or combinations of genes. For example, eye color and hair texture are phenotypes.
The evolutionary history of a species.
A variation or mutation at a genetic location.
A group of individuals that share a common social or physical characteristic.
A short molecular sequence added to a DNA sample under test. The primer separates out genetic material at specific marker locations.
The process of determining the order of the individual bases in a segment of DNA.
Human beings have 23 pairs of chromosomes. The two chromosomes in the 23rd pair are called the “sex chromosomes” (because they determine gender). A child inherits one sex chromosome from the mother (always an X chromosome) and one sex chromosome from the father (either and “X” or a “Y”). If the sex chromosome from the father is an “X”, the child becomes a girl. If the sex chromosome from the father is an “Y”, the child becomes a boy.
(Single Nucleotide Polymorphism): A change or mutation in a single base pair in a DNA sequence. SNPs are relatively rare, and are unrelated to the short tandem repeat (STR) mutations found on the Y chromosome. SNPs are used to define haplogroups.
A phonetic system of surname spelling used in genealogy.
stepwise mutation model
This model assumes that mutations always occur in single steps. For instance, if two cousins differ by DYS390=12 and DYS390=14, then we assume that two discrete mutations of one allele value have occured.
(Short Tandem Repeat): Repeats of short segments of DNA that appear sequentially at specific marker locations on different chromosomes. The number of Short Tandem Repeats at specific marker locations on the Y chromosome is the marker “value” that is reported in Y-DNA test results. For instance, 12 repeats of the sequence TCTA at marker DYS391 is commonly reported as DYS391=12.
A population sub-group.
The last name or “family name” in western European countries. Surnames were not used in most European countries until about 1200.
(Time to Most Recent Common Ancestor): The time, usually given in years or generations, back to a common ancestor shared by two or more individuals.
One of the two “sex chromosomes” carried by human beings. Women typically have two X chromosomes for the 23rd pair, whereas men typically have one X chromosome and one Y chromosome. Note that X chromosome DNA is not the same as mitochondrial DNA (mtDNA).
One of the two “sex chromosomes” carried by human beings. Only men commonly have Y chromosomes, which are inherited only from their fathers. Women do not have Y chromosomes, nor do they pass their father’s Y chromosomes down to their sons.