We inherit DNA from our parents and their ancestors in large sections. Within these large sections, there are groups of genes along each chromosome that have a tendency to stay together. These groups are part of gene linkage. These linked genes only allow the chromosome to split (for recombination) at either end of their linked section. The minimum size for one of these gene-linked sections is about 2.5 cM. These small segments then travel in larger groups.
Why are these minimum segments important? Research shows that these segments stay in the gene pool for dozens of generations. Over time, naturally occurring SNP mutations take place. These minimum inherited segments (MIS) can then be sorted into family groups.
For each Ancestor in our catalogue, triangulated ancestral autosomal segments have been identified. Taken together, these triangulated segments represent an autosomal haplotype (a genetic signature) that can be used to identify a descendant's genetic connection to an ancestor.
Not all ancestral segments are the same type. The segments can be categorized into three groups. The first category is Common to All. The Ancestors in the catalogue are predominantly European. One segment has been identified on chromosome 2 that triangulates across all surnames. This segment correlates to a Western Atlantic ethnicity and it is called the Western Atlantic Autosomal Haplotype (WAAH).
The next category is Shared. Some segments can be attributed to two or more surnames. There was considerable intermarriage between US families as the colonial period was a bottleneck genealogically and genetically. As two major families married, their combined DNA segments entered the gene pool and were reinforced as their descendants intermarried.
The third category is Unique. These shared segments cannot be attributed to intermarriage of families. Yet the resulting familial autosomal haplotypes are not composed of a single surname. In the case of Benjamin Franklin, the genetic proximity to his wife, Deborah Read and his mother, Abiah Folger, may make it impossible to distinguish between Folger, Franklin and Read DNA. Therefore, the haplotype represents the combined inheritance.
Example case study: Augustine Bearse was born in England in 1618 and died in Barnstable, MA before 1697. The Bearse family was chosen due to my familiarity with the genealogy and the debate surrounding Augustine's wife. His wife Mary was supposedly the granddaughter of the Chief of the Cape Cod Native American tribes. The goal is twofold. Identify the autosomal haplotype for the Bearse family and determine whether any of the ancestral segments have Native American ethnicity.
The Bearse haplotype contains 13 ancestral segments including the Western Atlantic Autosomal Haplotype (chromosome 2) which is common to all haplotypes in the catalogue. The 12 other ancestral segments are valuable for genealogical validation. It is highly unlikely that a descendant will match on all of the segments. Although ancestral segments survive over the generations, the randomness of their distribution makes it difficult for any one person to have received them all. Matching on just one segment unique to Bearse is enough to indicate and validate a relationship. Lack of a match could mean that an ancestral segment was not inherited or that a non-familial event (adoption, infidelity, etc.) has occurred and the individual's family tree is incorrect.
In order to investigate the origins of Augustine's wife Mary, each ancestry segment from the haplotype was evaluated for ethnicity. Only one segment had any Native American ethnicity. This ancestral segment is not yet available for a full match. With additional research, the segment could become available for matching. Once validated, it may help confirm Native American genes in the Bearse descendants.
While the amount of autosomal DNA received by each successive generation is only half from each parent, that does not mean that given enough generations a distant ancestor's genetic contribution will become negligible. Through genetic linkage, portions of DNA are inherited intact. Ancestral segments averaging 2.5 cM are passed from generation to generation as a minimum inherited segment (MIS).
OriginsConnector matching analysis is invaluable for the identification of distant ancestors.