Forensic Utility, Kinship Inference, and Population Genetic Structure of 57 Autosomal InDels in the Inner Mongolia Han Population

In the quiet work of forensic science, investigators often rely on the unique genetic fingerprints left behind in a crime scene sample. For decades, the standard tool for this has been the analysis of short tandem repeats, or STRs. These are sections of DNA where a specific pattern of letters repeats itself a variable number of times, creating a highly individualized code. While powerful, STRs have a weakness: the repeating patterns can be long, making them difficult to read if the DNA sample is old, damaged, or degraded. To solve this, scientists have turned to a different kind of genetic marker called an insertion or deletion, known as an InDel. These are tiny differences in the DNA sequence where a small piece of genetic code is either present or missing. Because these differences are so small, the DNA fragments needed to detect them are short and sturdy, surviving better in difficult samples than the longer STR markers. They also lack certain technical glitches that can confuse the results, making them a reliable backup tool for identifying people and determining family relationships.

A team of researchers at Southern Medical University recently set out to test how well a specific set of these InDel markers works within a specific community. They focused on the Han Chinese population living in Inner Mongolia, a region in northern China with a long history of movement and interaction between different ethnic groups. While scientists have studied the genetics of this group using other methods, there was a gap in knowledge regarding these specific short DNA markers. To fill this gap, the researchers collected blood samples from 197 healthy, unrelated individuals from the Inner Mongolia Han population. They used a commercial laboratory kit designed to look at 57 different InDel locations across the human genome, a number carefully chosen to provide a strong statistical picture without being overwhelming.

The first step was to ensure the markers were behaving as expected. The researchers checked to see if the genetic variations were distributed randomly within the group, a condition known as Hardy-Weinberg equilibrium, and confirmed that the different markers were not influencing each other. They found that the markers were stable and independent, meaning they could be used together to build a powerful identification profile. When they calculated the ability of these 57 markers to distinguish one person from another, the result was nearly absolute. The chance of two unrelated people having the exact same genetic profile across all these markers was so infinitesimally small that it is effectively zero for any practical purpose. Similarly, the markers proved highly effective at confirming or excluding a parent-child relationship, a critical function in paternity testing.

The team also looked at a more complex family question: how well these markers could identify full siblings. Unlike parent-child pairs, siblings share a more variable amount of DNA, making them harder to distinguish from unrelated people. Using computer simulations based on the genetic data from the Inner Mongolia Han population, the researchers tested how often the markers could correctly identify a pair of siblings. At a standard threshold used to suggest a relationship, the markers successfully identified nearly 98 percent of the simulated sibling pairs. Even at a much stricter threshold used to provide very high certainty, the markers still correctly identified a significant portion of the siblings. This suggests that while these markers are not a standalone solution for sibling testing, they provide valuable supporting evidence that can help solve difficult kinship cases.

Beyond individual identification, the study explored the genetic history of the Inner Mongolia Han people by comparing their DNA to that of 36 other populations from around the world, including groups from Africa, Europe, the Americas, and Asia. The researchers measured the genetic distance between the Inner Mongolia Han and these other groups to see how closely related they were. The results placed the Inner Mongolia Han firmly within the East Asian genetic cluster. When looking for the closest relatives, the data showed a particularly tight genetic bond with the Han Chinese population from Beijing. In fact, at the level of these 57 markers, the genetic difference between the Inner Mongolia Han and the Beijing Han was so small that it was statistically undetectable. This finding aligns with historical records of migration and interaction, suggesting that the Han people in Inner Mongolia share a very recent and close ancestry with the Han people in the capital region.

The study concludes that this set of 57 InDel markers is a robust and reliable tool for forensic work within the Inner Mongolia Han population. It offers a high degree of certainty for identifying individuals and testing parentage, while also providing a useful, though supplementary, method for identifying siblings. Furthermore, the research adds a new layer of detail to our understanding of the genetic landscape of northern China, confirming that the Han population in this region is genetically very similar to other major Han groups. By establishing these baseline numbers, the researchers have provided forensic scientists with the necessary data to use these markers confidently in legal and investigative contexts, ensuring that justice can be served even when DNA samples are challenging to analyze.