By Paul Rincon
BBC News science reporter
A team of scientists in Oxford is trying to prove whether families with the rare surname of "Christmas" all descend from a single male ancestor.
Henry Christmas has spent 50 years researching his surname
They want to compare the DNA of men from different Christmas clans to see if they are linked by a common genetic heritage as well as by their surnames.
This will be done by looking at similarities and differences in the male, or Y, chromosomes of volunteers.
The work is part of wider research on the links between surnames and DNA.
DNA analysis company Oxford Ancestors is currently appealing for volunteers to participate in the study and is being assisted in the effort by Henry Christmas, a former telecommunications engineer who has spent 50 years researching the origins and history of his own family name.
Professor Bryan Sykes, who is leading the study at Oxford Ancestors, told the BBC News website: "There are several interesting questions such as was there one original 'father' Christmas or were there several different ones?"
A bit of cheek
His team will be taking cheek swabs from those volunteers selected by Mr Christmas in order to extract their DNA.
Every male possesses a Y chromosome which can be inherited only from his father, so this package of genetic material represents a unique record of paternal inheritance.
"If it's a single family with one original founder, then most of them will have the same Y chromosome fingerprint. If there's more than one, we'll identify that," said Bryan Sykes.
"But generally this is the kind of name that, from experience, has one or very few founders."
The work forms a small part of a wider project being conducted by Professor Sykes on the genetic history of Britain.
Surnames can be remarkably informative in reconstructing the genetic family tree of the British Isles, especially those of moderate frequency that can be tied closely to genealogical records.
"Generally speaking, the rarer the name, the more likely it is to have one founder. Most surnames are moderate frequency," he explained.
"Many, even now, are clustered around the historical origin of the name.
"This gives you a way of measuring how much spreading and mixing and movement there has been over the last 800 years - because many English surnames started then."
Professor Sykes found about 70% of the men he studied with his own surname had near-identical Y chromosomes. The 70% were all descended from one man who lived in Yorkshire in the 13th Century.
The Christmas family name is established widely through the home counties, but there are two significant geographical clusters; one in Essex and one in Sussex.
"We will select volunteers from those two branches," said Professor Sykes.
"If you didn't have that genealogical information, you wouldn't have the first idea about those two branches or where they come from."
Some genealogy books state that the origin of the surname derives from "one born at Christmas". But Henry Christmas believes this is "too easy".
"The original spelling was 'Chrystmasse', which perhaps indicates Norman origin. There were also Huguenots who came over [from France] with that name," he told the BBC News website.
Professor Sykes said the study should also be able to show how people with the Christmas surname were linked by their genes to other lineages.
And it should connect the common male founder - if indeed there was one - with one of the major population groups that have settled in the British Isles over the ages.
But the technique can also reveal signs of female infidelity, turning up errant Y chromosomes that do not fit in the overall genetic tree for a particular lineage.