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DNA Family Trees

Tracing Your Ancestry Through DNA



Woman spitting into DNA collection tube


Popularized in recent years by its use in high-profile criminal investigations and paternity cases, DNA, deoxyribonucleic acid, is most commonly used to prove a relationship to an individual. New tests created in recent years, however, have also turned DNA into a popular tool for determining ancestry. As DNA is passed down from one generation to the next, some parts remain almost unchanged, while other parts change greatly. This creates an unbreakable link between generations and it can be of great help in reconstructing our family histories.

While it can't provide you with your entire family tree or tell you who your ancestors are, DNA testing can:

  • Determine if two people are related
  • Determine if two people descend from the same ancestor
  • Find out if you are related to others with the same surname
  • Prove or disprove your family tree research
  • Provide clues about your ethnic origin

DNA tests have been around for many years, but it is only recently that the cost of genetic testing has finally come down into the realm of possibility for the average individual interested in tracing their roots. Home DNA test kits can be ordered through the mail or over the Internet at a cost averaging $100-$400 per test. They usually consist of a cheek swab or mouthwash to easily collect a sample of cells from the inside of your mouth. You send back the sample through the mail and within a month or two you receive the results - a series of numbers that represent key chemical "markers" within your DNA. These numbers can then be compared to results from other individuals to help you determine your ancestry. [blockquote shade="yes"]Confused with all the talk of markers, mutations and haplotypes? See Genetic Basics: Understanding the Clues Found in Our DNA

There are three basic types of DNA tests available for genealogical testing. The first two test only the direct male line and the direct female line:

mtDNA Tests - Mitochondrial DNA (mtDNA) is contained in the cytoplasm of the cell, rather than the nucleus. This type of DNA is passed by a mother to both male and female offspring without any mixing, so your mtDNA is the same as your mother's mtDNA, which is the same as her mother's mtDNA. mtDNA changes very slowly so it cannot determine close relationships as well as it can determine general relatedness. If two people have an exact match in their mtDNA, then there is a very good chance they share a common maternal ancestor, but it is hard to determine if this is a recent ancestor or one who lived hundreds of years ago. It is important to keep in mind with this test that a male's mtDNA comes only from his mother and is not passed on to his offspring.


Y-DNA Tests - The Y chromosome in the nuclear DNA can also be used to establish family ties. The Y chromosomal DNA test (usually referred to as Y DNA or Y-Line DNA) is only available for males, since the Y chromosome is only passed down the male line from father to son. In other words, women don't have a Y chromosome! Tiny chemical markers on the Y chromosome create a distinctive pattern, known as a haplotype, that distinguishes one male lineage from another. Shared markers can indicate relatedness between two men, though not the exact degree of the relationship. Y chromosome testing is most often used by individuals with the same last name to learn if they share a common ancestor.

Example: The DNA tests supporting the probability that Thomas Jefferson fathered the last child of Sally Hemmings were based on Y-chromosome DNA samples from male descendants of Thomas Jefferson's paternal uncle, since there were no surviving male descendants from Jefferson's marriage.

Markers on both mtDNA and Y chromosome tests can also be used to determine an individual's haplogroup, a grouping of individuals with the same genetic characteristics. This test may provide you with interesting information about the deep ancestral lineage of your paternal and/or maternal lines.

A third type of DNA test that has become popular for genealogy purposes in recent years is the autosomal DNA test:

Autosomal DNA (atDNA) - Available for both men and women, this test surveys 700,000+ markers on all 23 chromosomes to look for connections along all of your family lines (maternal and paternal). The test results provide some information about your ethnic mix (the percentage of your ancestry that comes from Central Europe, Africa, Asia, etc.), as well as as helps to identify cousins (1st, 2nd, 3rd, etc.) on any line.

Next > What Can I Expect to Learn From the Tests?


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