According to the Department of Homeland Security, around 12,000 children who crossed the southern border of the United States are in the custody of their department. Attorney General Jeff Sessions stated on June 19 via the Washington Watch radio show that he is exploring the possibility of using DNA tests to verify the parentage of adults who accompanied these kids. The reason for identifying family relationships among these groups is to ensure the adults are truly the children’s parents and not traffickers. So how would it work?

Identifying Close Family Relationships Using DNA

In most of these cases, a paternity DNA test or maternity DNA test would be ordered to confirm or disprove the biological relationship. Results from this type of testing are used by courts every day to settle relationship questions and make decisions about child-support, custody, inheritance rights, adoption, and more.  It is also used as proof of relationship for immigration purposes by people applying for legal citizenship.

The Science of DNA Relationship Testing

Polymerase Chain Reaction (PCR) DNA testing is the type used in relationship cases. PCR targets regions in the DNA known as STRs (Short Tandem Repeats) that are highly variable. In a paternity test where the mother, child, and alleged father are tested, the child’s DNA should match both biological parents unless there is a mutation. Statistical calculations can be performed to help determine whether a genetic inconsistency at a single location (locus) is consistent with a mutation or an exclusion. Occasionally more than two genetic inconsistencies are observed and in those cases additional testing is performed. Most accredited labs examine a standard battery of STR loci, but can test additional STR loci when needed to resolve a case.

The power of the PCR DNA test is greater than 99.99%. Because results are obtained using statistical probabilities, the results can never show 100%.

SEE A BRIEF HISTORY OF RELATIONSHIP TESTING >

How Is This Different From Other Types of DNA Tests?

Most Americans are familiar with ancestry testing, but don’t know as much about relationship testing. A different type of DNA testing is used for ancestry and genetic-disease screening that uses SNP (Single Nucleotide Polymorphism) arrays. These tests use thousands of genetic markers, and the array usually includes AIMS (Ancestry Informative Markers), Y-chromosome markers, mitochondrial markers, ancient DNA markers, and more, depending on the type of test.

In contrast, non-coding “junk” DNA is used in relationship testing specifically to determine a biological bond between two people. This DNA does not provide information about traits like hair color or provide any health-related information. What analysts look for in a maternity or paternity test is whether or not the child inherited 50% of their DNA from the adult claiming to be their biological parent.

The Bottom Line

When performed by an accredited lab, DNA relationship testing is a scientifically- and legally-accepted method to establish a biological relationship between individuals. If it’s decided that testing would be useful to help resolve identification problems at the border, then it’s essential to know the science is sound.

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