produced a boy and a girl; and yes, they would be willing to test. Voila, we had our opportunity to help baby Charlote! Our mission to determine paternity
took a detour. Instead of a traditional paternity test, which is difficult without the alleged father, we looked to siblingship testing to establish paternity. A DNA sibling test is one in which the genetic material (DNA) of one person is compared to that of another person to determine the likelihood that they are related biologically as siblings. Individuals who share only one biological parent in common are called half-siblings. On average, full-siblings share 50 percent of their genes due to common inheritance, whereas half siblings share only 25 percent. A siblingship test requires a strong match in DNA on all or most markers of the two children from the previous marriage—where the father is undisputed—to that of Charlote, to determine if they share the same father. In half versus unrelated siblingship tests, the DNA of individuals with different biological mothers is compared to determine the likelihood that they share the same biological father. For best results, it is best that samples from both biological mothers be tested along with the children from both mothers. Tis enables us to determine exactly which genes the children inherited from their biological mothers, and it makes it easier to determine which genes were inherited from their biological father. Tis greatly increases the conclusiveness of the test. It is important to understand that,
unlike a traditional paternity test in which samples of the alleged father and child are both tested, it is not always possible to obtain a conclusive result in a DNA siblingship test. Tis is, in part, because the patern of inheritance and degree of sharing of genetic markers between siblings are not the same as that between a parent and child. In a siblingship DNA
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test, the degree of certainty that can be achieved depends upon who is available for testing, as well as the specific type of sibling relationship being tested. As a general rule, the more genetic information available, the greater the chance the test will be conclusive. In Charlote’s cases, it was advantageous to include two undisputed siblings from the previous marriage in the test. You see, if the DNA match from the children of the first marriage—where, again, the deceased husband is undisputed as the biological father—compared to Charlote’s DNA is strong enough, the deceased would have had to father Charlote. We decided a half versus unrelated siblingship test was our best chance to determine paternity. In the following table, you can see
where all five individuals were tested: Brandie and her daughter Charlote; in addition to the previous family of Amy, and her children Aidyn and Cydnee. Te results show which alleles the children received from their respective mothers, leaving the remaining alleles inherited from their father. Comparing the remaining alleles of all three children, we find a strong match that indicates a high probability that the established biological father of Aidyn and Cydnee also fathered Charlote. In fact, the probability that Charlote shares the same father as Aidyn and Cydnee is 99.935 percent, and strong enough for legal concerns such as social security benefits. Charlote and her half siblings share a
special relationship. Tey may sense that bond now, but will likely not appreciate it until they grow into toddlers and teenagers. For now, they will share play activities and learn about their dad. Later, they will learn how the DNA they share has brought them closer together for a lifetime. ❚
References: True and Factual Testing Event, ARCpoint Labs of Tempe, 2013
Back to Genetic Testing: How does a paternity test work?, Mei-Hsin Cheng, Stanford University
It is important to understand that, unlike a traditional paternity test in which samples of the alleged father and child are both tested, it is not always possible to obtain a conclusive result in a DNA siblingship test.
Gary F Patrone is CEO of ARCpoint Labs of Tempe, Phoenix and Mesa (Tempe-
AZ.arcpointlabs.com), and serves clients throughout the Phoenix Valley. Gary serves
both corporate and private clients in drug, alcohol, DNA, and on-site testing services; creates workplace policies for both the Department of Transportation and non-man- dated companies; and manages consortiums and random programs for corporate and pri- vate clients. Gary is an active member of the Tempe-South Rotary Club, an Ambassador of the Tempe Chamber of Commerce, mem- ber of the Business Development Committee with the Tempe Chamber of Commerce, and member of the Advisory Council for Brook- line College and PIMA Medical Institute. Gary has authored articles for DATIA, the Arizona Small Business Association, and writes a monthly column for the Arizona Republic.
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