Many brands claim to be able to accurately determine an individual’s ethnic origins. This has led to tens of millions of Americans taking their at-home ancestry tests. However, few of these Americans know exactly how the tests work.
The Sample
Typically, an individual will fill a tube with their saliva and mail it to whichever company they originally purchased the test from. The DNA sample then reaches a laboratory and one test or series of tests may be performed. In all of these tests, what is called a genotyping array (or SNP array) is utilized. This technology allows for the detection of thousands of small variations in an individual’s genome. These variations are compared to those of a reference group whose ancestry is known. The reference group consists of tens of thousands of individuals with a variety of ethnic backgrounds.
The Tests
A company may use a genotyping array for autosomal DNA testing, mitochondrial DNA testing, Y-chromosome DNA testing, or any combination of the three. In autosomal DNA testing, variations in the DNA of every chromosome but the sex chromosomes are analyzed and compared. This allows the consumer to receive information on the ethnic backgrounds of both their paternal and maternal lines. In mitochondrial DNA testing, DNA in the mitochondria (outside of the nucleus) is tested. Mitochondrial DNA is received solely from the mother so this test will only allow for an individual to receive information about their maternal line. In Y-chromosome DNA testing, only DNA from the Y sex chromosome is analyzed and compared. As the Y chromosome is passed down from father to son, this test can only be done on males and will only provide information about the paternal line.
Limitations
Though hundreds of thousands of variations in the genome may be analyzed when an ancestry test is conducted, these tests still have limitations and should not be used as full proof methods to determine ethnicity. Despite the many variations that are compared, these variations make up a relatively small portion of the genome. This means that all of an individual’s ethnic background may not be represented. Ancestry tests inform an individual of the origin of the DNA analyzed, not the origin of the entire genome. Further, some of these variations may not have been passed down by an ancestor and could be random mutations that occurred in the individual. This could lead to a consumer being incorrectly informed that they are of a particular ethnic origin. A much more common concern is that the reference group used by a company may not use many individuals of a particular ethnic background, possibly leading to unspecific or inaccurate results for minorities.
