DNA Detail for the Bird DNA Study

Date: [unknown]

This is the detail page for the Bird DNA Study. Genealogists may contact the project managers for specific research information.

Contents 1 Definitions 2 Methodology 3 DNA 3.1 Related 3.2 Unrelated 3.3 Undetermined 4 Results 4.1 △Triangulated matches 4.2 Statistically significant matches 4.3 Other matches of interest 5 Sources

Definitions

• MRCA = most recent common ancestor(s).
• cohort = a group of DNA samples organized around a shared characteristic.
• cohort-pair = two DNA samples from different cohorts that are tested against each other
• triangulated match = three sets of matches between three DNA samples in which the DNA segment of a particular chromosome is common to all three samples and the relationship between all samples is third cousin or greater.^[1]
• IBD match = a match between two DNA samples in which the minimum segment is at least 10 cMs, indicating a match that is "identical by descent" with a common ancestor within the last 500 years.^[2]
• sub-threshold match = a match between two DNA samples in which the minimum segment is 5 cMs, the minimum segment size for negligible false-positives.^[3]
• threshold match = a match between two DNA samples in which the minimum segment is 7 cMs, the historically accepted minimum segment size for a moderately confident likelihood of a single MRCA.^[4] For purposes of this study a threshold match which exceeds 9.99 cMs is an IBD match, though it is also included as a threshold match when calculating totals for threshold matches.
• multi-chromosomal match (MC) = matches between cohort-pair that occur on more than one chromosome.
• stippling = small matches on the same or opposite chromosome between two cohort-pairs as distinguished from another cohort-pair (which may or may not include one of the same samples from the first cohort-pair) with a match on the same or opposite chromosome upon a different segment.

Methodology

DNA matching was undertaken at GEDmatch using the default measures for One-to-One Autosomal Comparison except for the minimum segment cM size which was set to a numerical value of 5. Documented false positives were likewise eliminated.^[5]

When dealing with large data sets, telltale traces of ancient, degraded DNA commonality seem to be:

• statistically significant,^[6] valid matches^[3] between samples from different cohorts; and
• matches between different cohort-pairs along the opposite autosome; and
• stippling, a repetition of matches between different cohort-pairs on different segments of the same chromosome, particularly where those segments adjoin or are nearly- adjoined; and
• a pattern of sub-threshold matches among different cohort-pairs accompanied by one or more residual threshold matches.

As a rule of thumb, blocks longer than 4 cMs date from 500-1,500 years, while blocks longer than 10 cM date from within the last 500 years.^[2] Triangulated matches confirm existence of and/or identity of MRCA. Statistically significant IBD match rate strongly implies existence of MRCA within 500 years. Statistically significant threshold match rates below 10 cMs and/or valid match rates strongly imply existence of MRCA within last 1,500 years. Statistically significant multi-chromosomal rates are supporting evidence of an MRCA within last 500 years.

DNA

Related

Currently there are two cohorts of DNA descendants of Francis Bird and Jane Littleton of Rock Creek parish (1725) in modern Washington D.C. and historical Prince George's/Frederick/Montgomery Cos. in Maryland:

• Cohort 1 contains 15 samples from descendants of their their son John Bird, via their great grandson Francis Bird and his first wife Rhoda Schermerhorn, referred to as "Bird-#" when referenced individually; and
• Cohort 2 contains 8 samples from descendants of their daughter Mary Bird and her husband Benjamin Allison, referred to as "Allison-#" when referenced individually.

Numerous other familial samples were grouped into cohorts for purposes of testing. They are:

• Cohort 3 contains 3 samples from other descendants of Tabitha Littleton, referred to as "Tabitha-#" when referenced individually;
• Cohort 4 contains 6 samples from descendants of John Littleton Sr. and Margaret Riley, referred to as "Littleton-#" when referenced individually; and
• Cohort 5 contains 12 samples from descendants of Thomas Riley and Sarah Webb, referred to as "Riley-#" when referenced individually.

Unrelated

• Cohort B1 contains X samples from descendants of Thomas Bird and Sarah Empson of New Castle, Delaware, referred to as "NDB-#" when referenced individually.
• Cohort B2 contains 3 samples from descendants of Thomas Bird of Cecil Co., Maryland, referred to as "CMB-#" when referenced individually.

Undetermined

Finally, numerous geographical and/or clan-based samples were grouped into cohorts for purposes of further testing. They are:

• Cohort X1 contains 5 samples that extend the triangulated match on chromosome 16 w/ Bird-1/Bird-2/Bird-3/Bird-5/Bird-7 and are believed to originate near the Ulster plantation in the 17th century, referred to as "X1-#" when referenced individually.
• Cohort X2 contains 7 samples from descendants of various "Bell" families believed to have connections to the Ulster plantation, referred to as "Bell-#" when referenced individually.
• Cohort X3 contains 12 samples from descendants of various "Sheridan" families believed to have connections to County Cavan in Eire, referred to as "Sheridan-#" when referenced individually.

Results

△Triangulated matches

Cohorts 1 was tested against against a number of other samples to determine genetic relation:

1. vs. Cohort 2 shows a triangulated match among ▲Bird-1/Bird-2/Bird-5/Bird-7/Bird-9/Allison-5 on Chr. 14 @ 11.2 cMs and proves common descent from Francis Bird and Jane Littleton of Generation 1.
   
   
2. vs. Cohort 1 shows a triangulated match among ▲Bird-1/Bird-2/Bird-3/Bird-5/Bird-7 on Chr. 16 @ 18 cMs proves common descent from Francis Bird and Rhoda Schermerhorn of Generation 4.
   
   
3. vs. Cohort X1 shows a triangulated match among ▲Bird-1/Bird-2/Bird-3/Bird-5/Bird-7/X1-1/X1-2/X1-3/X1-4-4/X1-5/ on Chr. 16 @ 10.3 cMs proves common descent from an unknown Irish couple with a genetic match that is inclusive of the preceding match, appears to have originated near the Ulster plantation and suggests an MRCA sometime between 1606-1700.
   
   
4. vs. Cohort X3 shows a triangulated match among ▲Bird-5/Bird-9/Bird-12/Sheridan-5/Sheridan-6 on Chr. 6 @ 7.6 cMs and proves common descent from an unknown Irish couple. The two Sheridan samples are from Australia and have links to early 19th century County Cavan.

Statistically significant matches

1. The significance level of cohort-pair 1 & 2 is 19% for threshold matches, supporting common descent from Francis Bird and Jane Littleton.
   
   
2. The significance level of cohort-pair 1/2 & 3 is X% for threshold matches, supporting common descent from Tabitha Littleton.
   
   
3. The significance level of cohort-pair 1/2/3 & 4 is X% for threshold matches.

Other matches of interest

1. There is a single sample from a descendant of the Bird family of Somerset Co., Maryland that has a significance level of 13% for threshold matches when tested against Cohorts 1 & 2. This could indicate a pre-immigration MRCA , likely in seventeenth century Eire and presumably surnamed "Bird."
   
   
2. There is an intervening "Bird" surname in the descent of Cohort 2 from an unrelated Bird family. The significance level of cohort-pair 2 & 6 is 6% for threshold matches, suggesting Cassandra Bird's father Benjamin Bird was a grandson of the New Castle family. However, the lack of a statistically significant threshold relationship (<1%) between cohort-pair 1 & 6 proves the New Castle family is not related to the descendants of Francis Bird & Jane Littleton.

Sources

1. ↑ Wayne, Debby (2016). Genetic Genealogy Journey: Triangulating Autosomal DNA. National Genealogical Society Magazine.
2. ↑ ^{2.0 2.1} Coop, Ralph P. (2013). The Geography of Recent Genetic Ancestry across Europe. PLOS Biology 11(5):e1001555.
3. ↑ ^{3.0 3.1} Durand EY, Eriksson N, McLean CY. (2014). Reducing pervasive false positive identical-by-descent segments detected by large-scale pedigree analysis. Molecular Biology and Evolution.
4. ↑ Autosomal DNA match thresholds, International Society of Genetic Genealogy Wiki, edited on 17 August 2020.
5. ↑ Matching segments identified as possible "large-scale population pile-up region(s)“ indicative of identity by chance rather than identify by descent were eliminated." See Li H, Glusman G, Hu H, Shankaracharya, Caballero J, Hubley R, et al. (2014) Relationship Estimation from Whole-Genome Sequence Data. PLoS Genet 10(1): e1004144.
6. ↑ Tenny, S., Abdelgawad, I. Statistical Significance. [Updated 2022 Nov 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan.