Genetic genealogy (also known as molecular genealogy) uses genetic testing to enhance traditional genealogical research. It may well be the most exciting development in the field of family history in recent years. This how-to guide will give you a basic introduction to the subject. If you find some of the terms confusing, please see our glossary (terms in the glossary are shown in italics). If you’d like to dig into the subject more deeply, just click on the hyperlinked terms.
Gregor Mendel (1822 – 1884) conducted the first genetic research more than 150 years ago. In the twentieth century, understanding of genetics grew by leaps and bounds. Today, our more detailed knowledge of the subject allows for its use in genealogy.
There are a number of different DNA tests used in genealogy research. These are some of the most common types:
Paternal Lineage (Y-DNA) Testing
Y chromosome DNA testing is only performed on males (since only males carry the Y chromosome) and follows the paternal line of ancestry.
Surname Projects
Although not a type of testing, surname projects are an important resource for people interested in genealogy who have the same, or related, family names. Project members compare test results to increase their usefulness. When combined with more traditional research methods, surname group members improve their chances of discovering common male ancestry.
There are more good reasons why it may be beneficial to form or join a surname project if you are involved in Y-DNA testing:
Maternal Lineage (mtDNA) Testing
Testing of the maternal line involves studying the DNA found within the mitochondria. Children of both sexes inherit their mother’s mitochondrial DNA (mtDNA), and both can be tested, but only daughters are able to pass it along to the next generation.
Autosomal DNA Testing
Testing of autosomes (the 22 non-sex chromosomes) for genealogy is relatively new, and somewhat controversial. Also called admixture testing, autosomal DNA tests report actual percentages of various biological and geographical ancestries found within genetic samples (such as Native American, Sub-Saharan African, European, etc.).
To help search for their customers’ genetic cousins, some DNA testing companies store client test information in databases, along with additional test information from other sources. Tests results from new clients are automatically added to the database and compared with the many other test results already available, greatly increasing the chances of a positive match. Customers are notified when evidence of potential common ancestry is found.
Cyndi’s List - Genetics, DNA & Family Health
Cyndi’s List is one of the largest, most thorough, and popular links pages for genealogists.
Genetealogy.com
The term genetealogy, implying the intersection of genealogy with genetics, was coined by author Megan Smolenyak, an expert in the field.
The Genographic Project
This is a joint project of IBM and the National Geographic which uses large-scale voluntary gene testing to gain a better understanding of human genetic variation in a cultural context.
International Society of Genetic Genealogy
A non-commercial and non-profit international organization whose purpose is to promote and educate for the use of genetics as a tool for genealogists.
An Introduction to Molecular Genealogy
Part of a larger site on genetics from the University of Utah and Sorenson Molecular Genealogy Foundation, this approachable page discusses DNA and haplogroups using short, fascinating videos.
Kerchner's DNA Testing & Genetic Genealogy Info and Resources Page
An extensive links page with genetic genealogy topics ranging from the basic to the advanced.
Gates, Henry Louis. African American Lives [videorecording]. PBS Home Video: 2006.
Hart, Anne. How to Interpret Family History & Ancestry DNA Test Results for Beginners: the Geography and History of your Relatives. New York: ASJA Press, 2004.
Pomery, Chris. Family History in the Genes: Trace your DNA and Grow your Family Tree. Kew, Richmond, Surrey, UK: National Archives, 2007.
Smolenyak, Megan. Trace your Roots with DNA: Using Genetic Tests to Explore your Family Tree. Emmaus, Pa.: New York; Rodale: Distributed to the trade by Holtzbrinck Publishers, 2004.
Sykes, Bryan. The Seven Daughters of Eve. New York: Norton, 2001.
This brief glossary may help to clarify some of the terms you’ll encounter in your study of genetic genealogy. However, the cell biology that underlies genetic genealogy is complicated; if you’d like more complete information about these terms, simply follow the hypertext links.
What is a cell?
Cells are the smallest structural units of life that can themselves be described as living. All organisms of every size, from bacteria to whales, are composed of one or more cells. New cells are always formed from preexisting cells, and each cell contains all the hereditary information necessary to replicate the entire organism, no matter how large or complex.
What is DNA?
DNA (an abbreviation for the chemical name deoxyribonucleic acid) is an extremely large and complex molecule appearing as two long strands twisted around each other. They form a ladder-like structure called a double helix. DNA is found within the cell’s nucleus and mitochondria, and is the main component of chromosomes. DNA is present in all life forms. It encodes the genetic characteristics of organisms and transfers them to future generations.
What is a gene?
Heredity’s fundamental building block is the gene, a segment along a molecule of DNA. Genes contain coded instructions for the expression of hereditary characteristics like eye color, and whether hair is curly or straight.
What does genome mean?
The genome is all the genetic information of an organism such as a human being. Humans have two genomes: the chromosomal genome contained within the cell nucleus, and the mitochondrial genome located outside the nucleus in the cell’s internal fluid (cytoplasm).
What is a chromosome?
A chromosome is a thread-like structure, made of a single piece of coiled DNA, with hundreds or thousands of gene segments along its length.
As the illustration shows, chromosomes come in pairs. Humans have 46 chromosomes in 23 pairs.
What about XX and XY?
All humans, both men and women, have 46 chromosomes in 23 pairs. 22 of these pairs consist of very similar partners (called autosomes), one side of the pair from the individual’s father and the other side by the mother. The 23rd pair is different. Often referred to as the sex chromosomes, the 23rd pair determines the sex of the individual. Female humans have a 23rd pair of similar looking X chromosomes, while males have a 23rd pair of dissimilar X and Y chromosomes (as seen in the following image):
Reproduction is accomplished by special cells calledgametes (the eggs and the sperm). Eggs and sperm cells contain only half of each of the 23 pairs of chromosomes; in other words, half of the genetic information needed to make a new individual.
Since females have XX as their 23rd pair of chromosomes, a woman’s egg can only carry an X chromosome. Her egg will combine with a sperm cell that could be carrying either an X or a Y chromosome (since men have XY as their 23rd pair). Thus, the new 23rd chromosome pair of the child could be either XX (a girl) or XY (a boy).
What are Autosomes?
Autosomes are the 22 pairs of human chromosomes that do not determine sex (only the 23rd pair does that). These non-sex chromosome pairs shuffle and recombine their genetic information differently with each conception. In this way, new generations are sure to receive a random assortment of genetic information from each parent. No two individuals in the world have identical autosomal DNA (except in the case of identical twins).
What are Mitochondria?
Mitochondria are distinct organelles, sub-units, of human cells. They are found outside the cell nucleus floating in the cytoplasm, enclosed within their own membranes. Mitochondria function as the cell’s power supply by combining sugar with oxygen to produce the ATP which fuels the cell. While most DNA is contained in the cell nucleus, the mitochondria also have a small amount of their own genetic material called mitochondrial DNA or mtDNA.
What are Genetic Markers?
In genealogy, a genetic marker is any known and recognizable sequence of DNA that is useful in determining kinship. Commercial DNA tests for genealogy start by sampling as few as 10 genetic markers. In order to achieve higher resolution results, up to 67 markers can be checked. Costs of testing increases as the number of genetic markers being examined increases.
What is a Haplogroup?
A haplogroup refers to the many descendants of a single individual, who, far back in time, first showed a tiny and rare genetic mutation called a single nucleotide polymorphism (SNP). With time, these genetic mutations become genetic differences associated with specific isolated populations, allowing them to be differentiated from other groups.
Haplogroups can be thought of as large branches of humanity’s family tree. They are associated with broad geographic areas, like sub-Saharan Africa, or Europe. Every human is a member of a haplogroup. Population researchers use information obtained from many DNA samples to identify haplogroups, which helps them to understand patterns of early human migration. Using this same technology, genetic genealogy tests identify the haplogroup in your DNA, so that you can see area of the earth where your ancestral lines began, many thousands of years ago.
We hope this basic guide to genetic genealogy will pique your interest in this exciting new field. If you would like to know more, you can email us through our Ask-A-Librarian service or contact us at:
Maryland Department
Enoch Pratt Free Library
Central Library, State Library Resource Center
400 Cathedral Street
Baltimore, MD 21201
(410) 396-5468
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