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The Isaac Question and DNA Analysis
by John Plummer
Perhaps it is best to start by reviewing the fundamentals of genetics. We inherit discrete hereditary units from our parents, who in turn inherited discrete hereditary units from their parents, and so on ad infinitum. These units are called genes. Genes are made up of a molecule named Deoxyribonucleic Acid, or DNA for short. There are four varieties of DNA depending on which of four bases, Adenine, Thymine, Cytosine, or Guanine, A,T,C, or G for short, are incorporated. The arrangement of these four produces the genetic "code." The Genes in turn are part of a larger entity called a chromosome. The cell nucleus contains paired chromosomes; while the mitochondria in the cell outside the nucleus contain single chromosomes. The mitochondrial chromosomes, Genes, and DNA are passed on in an unbroken package, but only from one's mother; only in the female or matrilineal line. It is otherwise with the genetic material in the nucleus. Humans have 23 pairs of chromosomes in the nucleus. One of each pair is from the father; one from the mother. Initially it would seem that no matter how far we go back, there would be no more than 47 individual ancestors from whom we inherit genetic material: 23 on our father's side from whom we get a nuclear chromosome; 23 on our mother's side from whom we get a nuclear chromosome; and one additional ancestor on our mother's side (in the direct female line) from whom we get our mitochondrial chromosome. This would be true except for the phenomenon known as crossing-over. Crossing over doesn't occur with the mitochondrial chromosomes; but when the pairs of nuclear chromosomes are splitting up they often don't follow the proper dividing line - instead part of one chromosome will be exchanged with the corresponding part of the other in the pair. Thus we might inherit a gene or genes from each of our thousands of ancestors in Isaac Sheldon's generation. This would also mean there would be almost no chance of two descendants of Isaac Sheldon sharing any common genetic inheritance from him - except for one last factor. One of the 23 pairs of nuclear chromosomes is composed of unequal parts - one long, roughly "X" shaped chromosome; and one short, often "Y"shaped chromosome. These two are known as the "sex chromosomes." The female has 2 Xes; the male one X and one Y. A male receives his one Y only from his father, and so the Y chromosome is carried down in the male line. Crossing-over takes place for part of the Y chromosome; but part of the Y chromosome is carried down intact in the male line. It is this fact that made it possible for the Jefferson researchers to obtain meaningful results from DNA analysis. And it is this fact which promises fruitful results for Sheldon researchers. The Jefferson results were revealed in the journal Nature of 5 November 1998. Briefly, descendants of Thomas Jefferson's paternal uncle, Field Jefferson, were located; and the part of their Y chromosome which is passed down intact was examined. There were 19 places on this part of the Y chromosome that are found to vary among individuals. The Jefferson version of these 19 variables was very rare - not found in a sample of 670 Europeans, or of 1,200 people around the world. A descendant of the youngest son of Jefferson's reputed black mistress, Sally Hemings, had exactly the same combination of variables as Jefferson's uncle. Thus this descendant was not of African origin in the male line, but almost certainly a Jefferson descendant in the male line. Members of the Sheldon Family Association descend from several Sheldon immigrants. The three main branches come from Isaac Sheldon of Windsor, Connecticut 1652; Godfrey Sheldon of Scarborough, Maine by 1660; and John Sheldon of Newport, Rhode Island 1652. Godfrey Sheldon definitely came from Bakewell, Derbyshire, England. The other two have been thought to have come from Bakewell as well, but proof is lacking. If male line descendants of Godfrey Sheldon have the relevant part of their Y chromosome tested; if it is a relatively rare type; and if the male line descendants of Isaac and John have the same type; then it may be presumed that all three came from the same Bakewell family. Otherwise, they would not be from the same family, and it would be very likely that they came from another part of England. Theoretically two or more Sheldon families with different paternal ancestries could have originated from the small hamlet of Sheldon in the parish of Bakewell; practically, however, the author doubts that this is a common occurrence. The location and testing of English Sheldons, including ones from other parts of England than Bakewell, would be desirable, but not immediately necessary. The final solution of the Isaac question may be broken down into four steps. One - locating male line descendants of the different Sheldon immigrants. Two - obtaining DNA samples from as many of the above as possible. Three - analyzing the DNA from the above, preferably for all 19 variables. Four - interpreting the results of the analysis. The Sheldon Family Association has already done the first. The last is no problem whatsoever to carry out. A new facility now makes step two readily doable. Only step three would be at all difficult to have done right now; but it may soon be easily carried out as well. In 1996 Edwin M. Knights, M.D. and George A. Fischer, Ph.D. of Life Science, Inc. established that organization's GeneSaver Division, which has been featured in a number of reputable genealogical periodicals. Kits to take a drop of one's own fingertip blood are available by mail from GeneSaver (Box 1303, Grantham, NH 03753) for $5 for one to three samples, going down to $1 per sample for nine or more. The samples then should be returned to GeneSaver to be processed by lyophilization and preserved in specially sealed and marked containers. This step costs $57.50 per sample for the processing, $20 to $35 for a custom engraved preservation container, and $9.95 for postage for any number of containers. The samples are returned to the individual or organization. They are then ready for DNA analysis when that becomes available. Dr. Knights writes that he expects "a more competitive analytical climate in the near future" resulting in "a laboratory...that is both inexpensive and reliable." It would be advantageous for the Sheldon Family Association to obtain as many samples from male line Sheldons as possible. Multiple samples for each immigrant are desirable to guard against possibilities of illegitimacy and sample contamination, deteriorization, or mixup. Also, further useful information might be available because of possible small mutations in the last three and a half centuries. Once the first samples are obtained it might then be decided to seek immediate analysis, though that would be expensive and hard to secure. Or we might patiently wait until a laboratory tailored to our needs develops, probably in the near future. About the Author: John Plummer has a B.A. from New England College majoring in History and specializing in English History of the Tudor and Elizabethan periods. He is working on his M.A. in Early Modern European History at Columbia University specializing in the history of the English Puritans. He started genealogy research when he was 10 years old. He has worked as a free lance genealogist since graduating college in 1973. He belongs to so many historic and genealogical societies that he has lost count. He has published works on history and genealogy in The Connecticut Nutmegger, National Genealogical Society Quarterly, The American Genealogist, The New England Historical and Genealogical Register, Descendants of the Founders of Ancient Windsor Newsletter, and numerous family association newsletters.
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