DNA and the Landry Lines in North America

                                                         By Ben R. Londeree


The Landry Surname yDNA Project1 has identified three independent lines of Landrys living in North America.  Two lines migrated from France in the 1600s: 1: Guilluame Landry and 2: cousins Rene l’aine (The Elder) and Rene le jeune (The Younger) Landry.  These lines account for most of the Landrys in North America.  The third line came from Switzerland in the 1830s: two sons of Jean Jacques Landry.

First I want to set the stage for what follows.  Each person has 23 pairs of chromosomes.  Each person receives 23 from the father and 23 from the mother.  One pair of chromosomes is called the sex chromosomes because they determine the gender of the offspring.  The mother contributes an “x” chromosome and the father contributes either an “x” or “y” chromosome.  If the combined pair of sex chromosomes is “xx”, the child will be female.  If the combined pair of sex chromosomes is “xy”, the child will be male.  The remaining 22 pairs of chromosomes are called autosomal chromosomes.

There are a number of DNA tests.  The three tests that show the most promise in identifying ancestors are yDNA (from FamilyTreeDNA), mtDNA (from FamilyTreeDNA), and those which identify all of the mutations in a person’s autosomal chromsomes (SNPs) (Ancestry.com, 23andMe.com, and FamilyTreeDNA.com’s Family Finder Test.)  There are tens of millions SNPs.

Let me explain briefly the theory behind the use of the yDNA profiles in genealogy.  During the conception of males, the father’s “y” chromosome is passed on pretty much intact to his sons.  This process is repeated by his sons who pass this same “y” chromosome profile to their sons.  Since only males possess the “y” chromosome, the test only is available to males.  Females can trace their male lineage by having a close male relative provide a sample.  If two individuals have the same yDNA profile, they must have a common male ancestor.  Recall that I stated that the “y” chromosome is passed on pretty much intact.  Fortunately yDNA chromosomes are pretty stable.  Periodically a mutation will occur in one of the markers in the yDNA profile.  A marker is a specific location on the DNA molecule that is used for identification purposes.  The criterion is the number of units in the marker segment.  On average, a mutation will occur on a particular marker about once in every 500 male births.  A common yDNA profile consists of 37 markers so on average there would be a mutation on any of the markers every 13.5 male births (500/37 = 13.5.)  Therefore after several to many generations slight differences tend to show up in yDNA profiles.  The changes are cumulative so that after many generations, the differences between descendants of different lines become greater.  Therefore if two males have exactly the same yDNA profile, they have a common male ancestor within a small number of generations.  A difference on one marker would mean that their common ancestor probably is more removed.  With more differences between them, the common ancestor probably is removed even farther.  The yDNA test is considered to be the gold standard for identifying your earliest known ancestor.  The test only identifies that the participants have a common ancestor.  For the test to be useful in identifying the common ancestor, at least one of the comparison participants must know their lineage.

The mitochondrial DNA test (mtDNA) follows the mother’s female ancestors much like the male lineage for the yDNA test.  Both females and males can use this test.  The mtDNA results are more difficult to analyze because the mother’s surname generally changes with each generation.  In Quebec and France, at least some females retain their birth surname after marriage.  Female lineages are easier to follow in these circumstances.

 The test for SNPs (Single Nucleotide Polymorphisms) looks at your entire autosomal DNA structure.  Normally a nucleotide is paired with another specific nucleotide along a double stranded helix known as the DNA molecule.  The two specific nucleotides form a base pair.  Occasionally one of the nucleotides is replaced by a different nucleotide (a mutation or morphism) and the result is a SNP (pronounced snip).  This SNP will be passed down to descendants.  Unlike yDNA, autosomal DNA is made up of segments from both parents (about 50% from each).  Of course your parents received 50% of their DNA from each of their parents so you have some DNA from each of your grandparents (25%, more or less, from each.)  Similarly, you would receive 12.5%, more or less, from each of your great-grandparents, 6.25%, more or less, from your great-great-grandparents, and 3.125%, more or less, from your great-great-great-grandparents.  The more or less indicates that these are averages and for a particular person the percentage could vary a lot among the increasing number of grandparents.  So for ancestors more generations removed, the chance that you will have a particular SNP from a particular ancestor gets pretty small.  The beauty of these autosomal DNA tests is that you might be able to pinpoint children of a particular marriage where the unique SNPs of both parents are combined.  The success depends upon matching SNPs with somebody who knows their lineage.  As more people have the autosomal DNA test performed and post their known lineage, the potential for matches increases.

In the Landry Surname yDNA Project, individuals with known lineages back to Guillaume Landry, Rene l’aine Landry, and Rene le jeune Landry donated inside the cheek samples to determine their yDNA profiles.  Others who did not know their lineages participated as well.  Some of the individuals with known lineages were recruited but others participated because they were curious.  The samples were analyzed for each individual’s yDNA profile of 37 markers.

The results showed two distinctly different patterns of profiles and one that did not match any of the others.  One cluster of two individuals included a known descendant of Guillaume Landry.  Therefore the other person must have descended from Guillaume Landry as well.

The second cluster of nine individuals included the known descendants of Rene l’aine Landry and Rene le jeune Landry (Acadian Landrys).  This clustering is evidence that these two progenitors were related.  Stephen White used Catholic Church dispensations for the marriage of two descendants of the two Renes to conclude that if there was a common ancestor of the two Renes, he was not a father or grandfather.2

However, there was a common difference on two markers (representing one mutation) between two sub-clusters of the second cluster.  One sub-cluster of two individuals included a known descendant of Rene l’aine Landry.  The lineage for the other member of this sub-cluster was known back to 1730.  The second sub-cluster of seven individuals included two known descendants of Rene le jeune Landry and a third individual whose lineage tentatively is known (out of wedlock conception.)

The one individual with the unique yDNA profile recalls family stories linking him to Switzerland.  These stories would link him to Jean Jacques Landry whose sons emigrated from Switzerland to Louisiana in the 1830s.  A sample from a known descendant of Jean Jacques Landry would enable us to test this hypothesis.

To date, the Landry Surname yDNA Project has identified three unique Landry lines in North America.  Due to the small number of participants in the project, all possible lines may not have been identified.  If there are others, they probably arrived more recently, there are no living male descendants, and/or they haven’t been tested.

If you are interested in learning more about DNA testing and analyses go to: https://sites.google.com/site/wheatonsurname/beginners-guide-to-genetic-genealogy .


1 http://www.familytreedna.com/public/landryydnaproject/

2 White, Stephen A., English Supplement to the Dictionnaire Genealogique des Families Acadienes. Centr d'Etudes Acadienes, Universite de Moncton, Moncton, NB, Canada, pp. 194-5.