The problem is that most genes are mixed over very wide areas. List of published research on the consequences https://www.ucl.ac.uk/biosciences/understanding-genetic-ance...

You can see this by looking at genes with observable consequences such as lactose tolerance. While there are multiple genes for this AFAIK, the commonest is spread over a huge area.

Something as specific as "Danish" or "Italian" genes looks illusory.