The Sturdy Tree » Intro to DNA

Intro to DNA

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A General Introduction to DNA
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For genealogical purposes, DNA comes in four varieties: Y-DNA, X-DNA, mtDNA and atDNA. Y-DNA is the primary tool for tracing male ancestry but we will also look at mtDNA for our wives and daughters. And, yes, DNA does look a lot like the above image. DNA is used to trace the ancestry of family members because there is very little if any change (mutation) in the DNA over many generations. But mutations occur naturally and they are necessary for our genealogical purposes because they allow us to more accurately estimate and identify specific families and time periods.

  • Y-DNA (think Y-chromosome) is passed from father to son; daughters do not get a copy and cannot be tested (sorry, ladies). In genealogical times, Y-DNA is the simplest DNA to trace because it follows the same male path, father to son, as the family surname. Y-DNA identifies the direct paternal line of a male STURDEVANT. Y-DNA mutates at a relatively fast rate so it is also useful to estimate recent time periods.
  • X-DNA (think X-chromosome) is passed from mother to daughter and son. Yes, males get a copy, too. Remember, women have two X-chromosomes and men have one. Daughters get an X-DNA copy from both mother and father (1+1=2). However, sons get an X-DNA copy only from the mother because the father, instead, passes a copy of his Y-chromosome. X-DNA can be tracked like Y-DNA but with much more difficulty because a mother’s surname traditionally changes at marriage. The STURDEVANT DNA Project does not track X-DNA.
  • mtDNA (mitochondrial DNA) is present in all cells of both men and women. mtDNA is used in the surname project to help identify the direct maternal line of STURDEVANT children. Through a complex process, an mtDNA copy is passed by the mother to both sons and daughters. mtDNA is a good tool to trace ancestry from daughter or son to the mother, and the mother’s mother, etc. mtDNA is not passed from the father to children so cannot be used to track male lineage.
  • atDNA (autosomal DNA) is present in both males and females. atDNA (sometimes called auDNA) comes from the other 22 chromosomes. A portion of the father’s atDNA and a portion of the mother’s atDNA is passed to each child. Statistically, we say 50% of the atDNA is provided by each parent but that is only an average. Children may receive more or less from each parent. Usually the range varies from 40% to 60%. Because an individual’s atDNA is a combination of the atDNA of both parents, it can track both male and female close relations. Because of the random recombining, atDNA has little use in genetic genealogy beyond five or six generations. The STURDEVANT DNA Project does not track atDNA. Interesting aside: The proportion (percent) of atDNA received from each parent is easily calculated (cM/7440).

Y-DNA Details

Look, again, at the above DNA image. It is similar to a twisted ladder (called a double-helix). Y-DNA tests analyse and measure (or sequence) the rungs on the DNA ladder. The colored spheres represent molecules. Each rung may be different and is made of a specific number of the same three specific molecules (represented by the repeating green, blue and white spheres). There are a lot of these rungs (millions) and they occur in a specific, identifiable pattern. A rung is called a Short-Tandem Repeat (STR or “marker” for short). If there were no mutations, markers at specific locations always have the same number of the same repeating molecules. A mutation, generally, causes one more or less repeat at that location.

Standard Y-DNA tests measure 12, 25, 37, 67 or 111 specific markers. The more markers tested, the more accurately we can differentiate between family members which means we can more accurately predict and identify family members. The STURDEVANT DNA Project needs at least 37 markers but 67 or 111 is even better to differentiate between haplotypes.

The Y-DNA test results for our project can be found on the Y-DNA Classic Results page.  The table will open in a new tab so you can refer to it during the following discussion.

Haplotypes

A haplotype is the combination of the values for all of the markers for an individual. Each row of the Classic Results table is the haplotype of a tested project member who is identified by a Kit number. My haplotype is identified by Kit H1011 and consists of the test value at each of the markers (STR). For example, the first marker measured in Y-DNA testing is DYS393. If a Y-DNA test reports DYS393=13, it means marker DYS393 has a pattern of 13 repeating sets of the same molecules (nucleotides). As many as 110 additional markers may follow DYS393. Each marker has a value that represents the number of repeating nucleotides.

I am a descendant of William of Norwalk, Connecticut Colony. Since he shared copies of his Y-DNA with his son(s), all male descendants of William of Norwalk will have a similar haplotype. That means, with certainty, when your haplotype matches my haplotype, you are my father, grandfather, brother, or male cousin. We share a common paternal patriarch and we share copies of the same Y-DNA haplotype and haplogroup.

Haplogroup

A haplogroup identifies a major branch that grew from the trunk of the human genetic tree (called a “phylogenetic tree” or “haplotree”). Ancient humans originated in Africa and migrated to other parts of the globe over a period of many thousands of years. Geneticists track migrations by haplogroup to determine the migration paths of major populations. They study migration patterns by analysis of haplogroup distributions and movements over time.

Just as STR markers identify a haplotype, a haplogroup is identified by a SNP (pronounced “snip”). A SNP is a marker that very rarely mutates and, therefore, can be considered genealogically unique. Because of their stability, SNPs exactly locate our place on the human family tree.

Just as a branch sprouts into limbs, a haplogroup is further divided into groups called “clades.” If the limb has a smaller branching limb, the latter is called a “subclade” of the larger clade. Clades are like limbs sprouting from a branch, ultimately dividing into twigs and leaves (your individual haplotype).

The haplogroup column of the Classic Results table is a combination of the actual haplogroup and a limb called a “clade.” A clade may be identified by the last or most distant unique SNP, called the “terminal snip.” The terminal SNP is that leaf way out there at the end of the limb. We us a shorthand terminology to identify the haplogroup and clade. For example, “I-L22” is an example of the “L22” clade of the “I” haplogroup. If a person test positive for a “downstream” SNP, it can generally be presumed that they will test positive for certain “upstream” SNP without being tested for that SNP. For example, “L22+” infers “M253+”. By this means, given a group of person of the same clade, when one member of the group tests positive for a subclade, then all members of that group may be presumed to test similarly (i.e., the member of the subclade may be a surrogate for the other group members).

Known STURDEVANT families belong to two major haplogroups, haplogroup “I” (most DE spellings) and haplogroup “R” (most TE and DI spellings) but, there are many exceptions (see the Classic Results table. My haplogroup is “I” and my clade is “L22,” a subclade of the larger M253 clade. L22 is a “down stream”  SNP that identifies a subclade of M253. When looking at test results, a + (plus) or – (minus) after the clade means a positive or negative test result, respectively, for that SNP. Persons who genealogically identify their pedigree to the same ancestor, will have the same haplogroup, clade and haplotree. Their haplotypes will match exactly or vary by only a few STR markers. Exceptions may be adoptees, name changes, etc. (often called non-paternal events or NPE).

Okay, look again at the Classic Results table. Here is the rest of the story:

  • Group: A logical collection of all members of the same haplogroup and haplotype within the project. Examples are I-L22 and R-M269. Each kit (member) is placed in a group determined by their haplogroup and haplotype. The purpose is to identify specific family lineage having similar haplotypes. Almost always, each group will have paternal ancestry leading to the same patriarch. Groupings will be different in other projects depending on the study purpose of the project.
  • Min, Max, Mode: In any group, Min (minimum) and Max (maximum) identify the smallest and largest values, respectively, in the group for that marker. Mode identifies the most common value of a specific marker. It is the value that can usually be expected at a specific location in the haplotype. Mode values are important because they infer (or reconstruct) the marker value for the common group ancestor. The aggregate of all modal marker values infers (or reconstructs) the haplotype of the common group ancestor. Colors, peach and plum, identify values, respectively, above and below the modal value. Other individuals (kits) with the same Mode values, and within Min and Max values, are very likely to share a common ancestry with other group members. At least three group members are required to identify Min, Max and Mode values.
  • Ungrouped: The ungrouped kits are those kits that lack sufficient information to identify a specific group.
  • Ungrouped Family Member: These are the welcome family members whose Y-DNA does not match a STURDEVANT patriarch. They are family researchers interested in STURDEVANT genealogy but do not have a STURDEVANT patriarch.
  • Haplogroup: As discussed above. Red identifies inferred values and green identifies tested (proven) values. Inferences are determined by the values of tested STR markers and are almost always correct.
  • Genetic Distance (GD): Not on the results table, GD must be calculated. GD may refer to either a single marker or the entire haplotype. It represents how closely two markers or two haplotypes match. GD is the value of the differences between any two haplotypes at any marker. For example, look at kits H1011 and H1923. The GD at DYS570 is 1 and at DYS712 the GD is also 1. Therefore, the GD between these two haplotypes is GD=1+1=2 (very close at the 111 marker level).

mtDNA Details

Much of the above explanation is also true for mtDNA. The STURDEVANT DNA Project records but does not track mtDNA because it is only indirectly related to the male lineage of the STURDEVANT surname. mtDNA haplogroups are defined similarly but are not the same groups as the Y-DNA haplogroups. mtDNA results may be of interest to family members or other project members who are researching a maternal lineage. Project members who have taken an mtDNA test can find their test results at the mtDNA Results page. Researching mtDNA may help identify a female member or ancestor who is a descendant of a mother of a STURDEVANT.

Take a look at the mtDNA Results page.

  • Haplogroup: mtDNA Tested Values are provided. Although some of the names may be similar, these haplogroups are not the same as the Y-DNA haplogroups.
  • HVR1 Mutations and HVR2 Mutations: These two columns identify how the tested mtDNA differs from a pre-selected, arbitrary standard value. Each value listed identifies a mutation from that standard. Values that match the standard are not listed.
  • Note: the Coding Region column is not displayed because it may contain personal information that should not be made public.

A note about haplogroup terminology

Besides arcane jargon, there is also confusion caused by differing terminology. Genetics and genetic genealogy are new and fast growing fields of study by both professional and hobbyist practitioners. These fields are growing so fast that information is often out of date and the latest information cannot be found. There are several concurrent efforts to develop and update a haplotree. Often researchers use names and terminology developed from their own research. Similarly, SNP locations and subclades may move and new subclades will be found. In this project, we will try to adhere to the terminology used above and by FTDNA.

Conclusion

If you are still reading this, congratulations are in order. Genetics is a complex field and I apologize for any errors or omissions I may have made in the above lengthy explanation. Mistakes are mine alone. My intent is to develop this page as a tutorial for The STURDEVANT DNA Project. I will appreciate any comment or constructive criticism that you would share. Please leave a reply below.

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