Listeners to the More or Less programme on Radio 4 have been challenging me to answer any fiendish question they can throw at me.

A question about Jesus's genealogy was rather interesting and the answer has astounding ramifications.

The Bible says Jesus was a descendant of King David. But with 1,000 years between them, and since King David's son Solomon was said to have had about 1,000 wives and mistresses, couldn't many of Jesus's peers in Holy Land have claimed the same royal ancestor?

Theory tells us that not only would all of Jesus's contemporaries be descended from King David, but that this would probably be the case even if Solomon had been into monogamy.

We can make this sort of prediction because over the past 15 years or so, these ideas have been studied as part of the research into understanding patterns in our own genome.

The most successful approach has been to go backwards in time, taking a sample of people and imagining the patterns of inheritance in their ancestral family tree.

When applied to the question of who is descended from whom, the results can surprise even the professionals.

That's because geneticists normally study biological information - DNA - that people inherit from just one of their parents.

Just like a surname, or the male lines of descent quoted in the Bible, these generate lineages that shrink or expand rather slowly. That's why we expect the proportion of Smiths in the phone-book to fluctuate only a little from decade to decade.

The surprise comes if we look at inheritance from both parents. Here, the numbers change drastically as the generations go by. For instance, we have two parents, four grandparents, eight great-grandparents, and so on.

Each generation back, we multiply the number by two. This leads to what is called an exponential increase: 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024 and so on.

It's not long before we hit huge numbers. Take the specific case of Jesus and King David.