GENETIC GENEALOGY
The Y-Chromosome and Genealogy.
The y-chromosome is inherited more or less unchanged from father to son to grandson, indefinitely. Thus it lends itself well to determining if two males are likely to share a common ancestor through male links.
Chromosomes contain the DNA that determines our inherited characteristics, and the y-chromosome is one of 46-chromosomes in the nucleus of each of the cells of all human males. Most chromosomes, including the two x-chromosomes possessed by females, get recombined or shuffled each generation before being passed down to offspring. But the y-chromosome is unique in remaining more or less unchanged when passed from father to son. Thus while most chromosomes will contain a random mixture of genetic codes from your grandparents and great-grandparents, a male's y-chromosome will be identical or nearly identical to that of his father, grandfather, great-grandfather and beyond for countless generations.
Unchanged must be qualified by "more or less" for two reasons. A small part of the y-chromosome (at the ends) does recombine with the x-chromosome, but for genealogical purposes we can ignore that portion. And, as with all the chromosomes, mutations occasionally occur. Otherwise all males would have identical y-chromosomes, making them useless for genealogical purposes. By looking at markers or specific locations on the y-chromosome, we can compare individuals and support or disprove suspected genealogical relationships. Since surnames tend to be inherited in the same manner as y-chromosomes (from father to son or patrilineally), y-chromosome testing lends itself particularly well to surname studies.
There are several approaches to using the y-chromosome in family studies. Early on, testing companies encouraged people to be tested with expectations of finding matches to previously unknown distant relatives in the databases of people tested. This hope has proved illusory. Testing 10 or 12 markers, those with common sets of markers (haplotypes) may find perfect matches to dozens of individuals in the current databases. But those matching individuals are unlikely to be related within any meaningful genealogical timeframe. For example, members of my great-grandmother's Hamman family have common haplotypes that so far have been matched (12 out of 12 markers) with nearly 90 others in the Family Tree DNA database, but none of those others appear to share a common ancestor within thousands of years. For now, and for many in the indefinite future, those who hope to use y-chromosome testing to expand their family tree by finding random matches are likely to be disappointed.
A different approach is to use y-chromosome testing to focus on certain well-defined puzzles or hypotheses. Our Hamman family study began as we tried to answer two questions. (1) Did the Hammans who settled in southwest Kosciusko County, Indiana (USA) share a common Hamman ancestor with my Hammans who settled in northeast Kosciusko County? And (2) were several Hammans who settled in Stark County, Ohio and De Kalb County, Indiana brothers of my ancestor who settled in northeast Kosciusko County, as suggested by a semi-fictionalized family history written in the 1920s and known as the Hamman fable? Y-chromosome testing answered the first question in the negative and strongly supported an affirmative answer to the second question. Descendants of two Hammans known to be descendants of the David Hamman who settled in southwest Kosciusko County matched each other perfectly but were completely different from three descendants of Jacob Hamman who had settled in northeast Kosciusko County, who in turn matched perfectly among themselves. In addition, descendents of three different Hammans who had lived in Stark and/or De Kalb County were a perfect match for the three descendants of the Kosciusko County Jacob Hamman, thus strongly supporting the Hamman fable.
Another common approach is to establish a surname y-chromosome study and invite any male sharing the same surname (including variant spellings) to participate. Our Hamman study has evolved in this direction. The testing companies encourage this approach by giving discounts to surname groups and publicizing the fact that specific surname groups exist. As of February 2005, we have found seven separate Hamman lines and expect to discover more. Eventually, we hope that some of the shallow Hamman lineages (dating back to only about 1800) will find connections to larger existing Hamman lineages, perhaps thus making connections to immigrant ancestors. In a Bachmann/Baughman study, we have already established that a number of Bachmanns living in Switzerland today share common ancestors with American Baughmans whose ancestors immigrated in the early 1700's. Without the paper genealogy, the exact connections may never be established, but at least we have clues as to where we should concentrate our research efforts. And knowing that two branches sharing the same last name do not share a common ancestor may result in less time wasted searching for possible connections that do not exist.
Females cannot participate directly in y-chromosome studies, having no y-chromosomes. However if they wish to compare their father's patrilineage, they can help sponsor their father or a brother or other patrilateral relative of their father.
Last Updated: Feb 2005; Copyright 2004-2005, Philip Ritter