Genetic genealogy companies sell DNA tests that can identify unknown relatives and reveal traces of your personal genetic heritage going back tens of thousands of years. But one still needs to think of them as a set of tools, each of which does a specific job. The current generation of DNA tests are rarely a one-stop solution to our key family history questions, though over the past decade the questions that the tests can address have become increasingly complex. On the horizon, though, is a comprehensive universal DNA test that will become the first port of call for any determined genealogist.

The next generation whole genome test has been promised by scientists for some years, but it has yet to arrive. Until it does, we manage with the current set of tests, each of which is fit for a specific purpose.

By far the most popular genealogical DNA test is the Y-chromosome test. Only men have this chromosome, and as it’s handed down from father to son it mimics the transmission of the surname from one generation to the next.

When you compare the Y-chromosome results of a group of men with the same surname they will cluster into different groups each with matching DNA, a sure sign that each group shares a common male ancestor and hence belong in the same family tree. There are more than 6,000 Y-chromosome surname projects underway worldwide today which together include several tens of thousands of different surnames.

While the vast majority of surnames will be revealed as having a single dominant ‘genetic signature’, usually between a quarter and a half of name-bearers – for English surnames – will have acquired a different Y-chromosome heritage at some point since the period more than 600 years ago when they became fixed. This may seem a disadvantage, but in fact it’s not: two men holding the same surname and sharing an unusual DNA result can be sure they do so because they are closely connected within the same branch of the wider family tree of the surname.

There is a female line equivalent to the male-only Y-chromosome test known as the mitochondrial DNA test. This is a mirror image of the Y-chromosome test except that it reveals connections along the direct maternal line rather than the direct paternal line. This test is hard to use simply because of the time one needs to invest to track one’s female line, where the surname changes every generation and where making sure that you are tracking the correct family in each generation can be complex and uncertain. This test can, however, be taken by both men and women.

Increasingly useful is a newer close cousin DNA test, marketed variously as a Family Finder test or a Relative Finder test. This test can look across all lines, scrutinising a sample of DNA in detail and comparing it to every other sample in the test company’s database. While these tests have only been on the market for a couple of years they are growing in popularity. At the moment the results often reveal only distant connections – potential fourth cousins, descendants of one of your 32 pairs of great-great-grandparents – which are difficult to research and document. But the databases of results are growing fast, and as they do so year on year they will become more efficient at generating stronger and closer matches.

All the above tests are useful for advancing your genealogy, for helping you document your ancestors and create family trees. But way beyond that relatively recent timeframe, DNA testing can throw up insights into your ‘deep ancestry’, the story of how the line of your direct maternal ancestor – and if you’re a man, of your direct paternal ancestor as well – spread out of Africa and around the globe.

If you’re of European descent, these results might tell you when those ancestors came into Europe and where they sought refuge during the last Ice Age 12,000 years ago. You can purchase specific tests to look at this aspect, or glean information about it from the standard Y-chromosome and mitochondrial genealogical test results.