Paleoanthropology, genealogy and the miracle of DNA. Part Four.

Tests purchased from FamilyTreeDNA (Houston)

	Y-chromosome (STR)	Mitochondrial	Autosomal (Family Finder)
What is tested?	Y chromosome DNA mutations (short tandem repeats, STR). See note #3.	Mitochondrial DNA mutations.	Single Nucleotide Polymorphisms (SNPs) from 22 pairs of autosomal chromosomes. See note #7.
DNA inheritance	Passed on by the father to sons only (hence only men can be tested)	Passed on by the mother to all children (& thus both men & women can be tested)	Inherited from both maternal and paternal lines (men & women can be tested)
Level of test	Four marker sequences; 12, 25, 37, 67. Highest level (111) was not included.	Full Mitochondrial Sequence (FMS) test which sequences the HVR1 region, the HVR2 region and the Coding Region. See note #4.	710,000 pairs of locations (SNPs)
Raw data	Number of sequence repeats (allele) at a given marker position (DYS).	Usually reported as differences from the revised Cambridge Reference Sequence (CRS)
Genealogical goals	Identify male relatives with a common paternal ancestor	Identify distant relatives with a common maternal ancestor	Identify relatives with a common ancestor
Genealogical/ historical timeframe	Recent to hundreds of years	Hundreds to thousands of years. See note #5.	Up to five or six generations (circa 100 – 150 years)
Close matches	The genetic “distance” between you and the match are expressed as “Steps”. See note #1.	Matches are likely to be very distant. See note #6.	Predicted relationships defined by autosomal DNA matched (in centiMorgans) & the longest matched segment. See notes #8 & #9.
“Deep ancestral” (archaeological) goals	Determine paternal line ancestral haplogroup (see note #2). Predicted from STR results. See note #3.	Determine maternal line ancestral haplogroup	Determine possible geographic origins by comparing results with world-wide type-populations. See note #10.
“Deep ancestral” (archaeological) timeframe	Usually tens of thousands of years	Tens of thousands of years	Hundreds to 2,000 years (up to about 80 generations).

Notes:

1)  For the various levels of  Y-chromosome STR test, the steps between the subject and a match equate to the number of markers that match as follows:

“Step” level	Number of markers used in the FTDNA tests
	12	25	37	67
0	11/12	25/25	37/37	67/67
1	12/12	24/25	36/37	66/67
2	NA	23/25	35/37	65/67
3	NA	NA	34/37	64/67
4	NA	NA	NA	63/67
5	NA	NA	NA	62/67
6	NA	NA	NA	61/67
7	NA	NA	NA	60/67

2)  Haplotype =  a set of closely-linked genetic markers which tend to be inherited together. Haplogroup = all of the descendants of a single individual who first showed a particular unique genetic characteristic. Haplogroups characterize the early migrations of specific population groups. Individuals with the same genetic mutation or "marker" can thus be linked back to the population where the marker first made an appearance.

3)  A Y-chromosome Single Nucleotide Polymorphism (SNP) test is available if either (a) the error in the haplogroup prediction from the STR test is high or (b) if more detail is required about the exact position within the haplogroup (aka “Deepclade”test).

4)  Mitochondrial DNA (mtDNA) has two major parts, the control region and the coding region. The control region is the hypervariable region (HVR) which is relatively fast changing. It may be further divided into two Hypervariable regions, HVR1 and HVR2. The coding region is the part of the mtDNA genome that contains genes and is believed to be slower mutating than the control region. Often, it is the mutations that are found in the coding region that are used to define the haplogroups

5)  Mitochondrial DNA mutations typically occur only once every 50 generations or about 1000 years.

6)  For an MtDNA match, the time window and confidence level increases with the higher resolution tests.

Matching Level	Maximum # Generations to MRCA	Confidence Interval
HVR1	52 (about 1,300 years)	50%
HVR1 & HVR2	28 (about 700 years)	50%
HVR1, HVR2  & Coding Region	16 (about 400 years)	90%

7)  Autosomal short tandem repeat (STR) tests are available but more often used in paternity testing etc. and are not normally offered to genealogists.

8) Autosomal matches are quantified using two measurements.

(i)  Shared cM - This is the sum of the autosomal DNA, given in centiMorgans (cM), that you and your genetic match share. When you share DNA segments with larger cM values with a match, your common ancestors are likely to come from generations that are more recent.

(ii) Longest Block - This is the largest DNA segment given in centiMorgans you and your genetic match share. A DNA segment (block) that is between 5 and 10 centiMorgans (cM) implies shared ancestry. A block that is 10 centiMorgans or larger indicates conclusive shared ancestry.

9) Matches are then grouped by predicted relationships:

(i) Relationship Range. This represents the upper and lower limits to the predicted relationship. The relationship is predicted with high confidence to fall within these limits.

(ii) Suggested Relationship. This is statistically the most likely relationship based on the amount of sharing between you and each match.

10)  This compares the subject’s autosomal signature to a world DNA population database which reflects the last 100 to 2,000 years (about 4 to 80 generations).  The test can detect small traces of genetic ancestry as low as 3% (about 5 to 6 generations) from a distinct Continental group. The continental groups and subgroups are based on genetic similarities and do not precisely match geographical regions. Similarly, the populations are strictly selected “type groups” designed to collectively represent the human genome. However these representative groups are not yet all-inclusive and more are gradually being added to the global database.