Is it possible to calculate my late grandfather’s DNA results?
QHow do ethnicity percentages work on a DNA test? Sadly, my grandfather is no longer with us, but knowing my grandmother, mother and uncle’s test results, is it possible to work out what my grandfather’s would have been had he been alive to get the test done?
For instance, if my grandmother has 45 per cent of DNA from ‘X’ region but my mother has 60 percent of ‘X’, does this therefore mean that my grandfather had at least 15 percent of ‘X’? Jennifer Shelden A DNA companies estimate ‘ethnicity’ by comparing your DNA to reference datasets comprising people who have known ancestry from specific countries or regions.
The populations are collected from publicly available datasets and from the DNA companies’ own customer databases. However, because each company uses different reference populations and they each have their own proprietary algorithms, the results for the same person can vary considerably from one company to the next.
The results are generally accurate at the continental level, but less reliable at the country or regional level. The high percentages are generally more accurate than the small trace percentages, which are often just noise.
Endogamous populations, where people have been marrying within their own community for hundreds of years, tend to stand out as distinct genetic clusters. For this reason Jewish ancestry, and sometimes Finnish ancestry, can be detected with reasonable confidence. If your results indicate that you are 50 per cent Jewish, then you are likely to have a Jewish parent. Otherwise the percentages do not generally correspond to a person’s known family history. There can be wide variations in the results for parents and children, and for siblings. For example, on AncestryDNA ( dna.
ancestry.co.uk) I am 21 per cent British, my dad is 8 per cent British and my mum is 58 per cent British, yet all our known ancestry is from Britain. The discrepancies for grandparents would be even greater. As the companies add more reference populations and improve their methodology, you can expect to see your percentages updated.
Just as I was writing this reply, I got a preview of my updated results at AncestryDNA. The regions and percentages have changed dramatically. I am now 94 per cent England and Wales, my dad is 62 per cent England and Wales, and my mum is 84 per cent England and Wales. Debbie Kennett