Yes, using a special type relationship DNA test referred to as a Genetic Reconstruction Test can help determine whether two people are half-siblings or cousins, but the accuracy depends on the type of test and the number of genetic markers analyzed.
Half-Siblings or Cousins #
- Half-siblings share approximately 25% of their DNA because they have one biological parent in common.
- First cousins share approximately 12.5% of their DNA because they have grandparents in common but not a direct parent.
A Siblingship DNA Test calculates a Half-Sibling Index (HSI) to compare genetic markers and determine the likelihood that two individuals share one parent. If the HSI is much greater than 1, it supports a half-sibling relationship. If it is close to 1, the results are inconclusive.
For cousins, a standard siblingship test will not provide a clear answer because cousins share fewer genetic markers. In these cases, an Genetic Reconstruction DNA Test (which includes additional relatives like a known full sibling or a parent) can provide stronger evidence.
Example: #
- Sarah and Emily suspect they are either half-sisters or cousins. Their HSI is 28.4, meaning they are much more likely to be half-siblings than cousins.
- Jake and Ryan suspect they are half-brothers, but their HSI is 1.2, which is too low to confirm a half-sibling relationship. Since cousins can have a similar score, further testing (such as adding another relative) would be needed.
If you need to differentiate between half-siblings and cousins, it’s best to include a parent’s DNA (if available) for a more accurate comparison.