Wednesday, June 9, 2010

Y-DNA Testing

Y-DNA refers to the DNA found on the Y Chromosome. It is contained in the cell nucleus of all males. All healthy humans inherit 23 Chromosome Pairs from their parents. The last two are the sex chromosomes, or the X and Y. Only males inherit the Y chromosome, so it can only be used to trace the direct paternal line. Simply speaking, a man inherits his Y chromosome from his father who inherited it from his father who inherited it from his father and so on. Testing of this Y-DNA can reveal the ancient origins of a person's direct paternal line. It can also be of great genealogical value since the Y-DNA traditionally follows the same inheritance pattern as surnames. As the surname is passed down from male to male, so is the Y-DNA. Used in conjunction, a male can often identify which ancestral line he belongs to by matching with others of the same or similar surnames. Though not guaranteed, an adoptee may even find success in discovering his biological surname by testing his Y-DNA. Some testees have not yet found success with this type of testing due to the lack of matches in the databases. However, time should rectify this problem for most with the growing popularity of DNA testing. For cultures that did not utilize surnames in the traditional way until the 20th Century, such as Scandinavia, the Y-DNA can still be useful in identifying probable origins and migration patterns.
Upon testing your Y-DNA you will receive a list of the short tandem repeats (STRs) contained on your Y chromosome that determines your haplotype. You may also be assigned a haplogroup based on single-nucleotide polymorphisms (SNPs) contained in your Y-DNA. Matches are measured by genetic distance (GD) and can estimate the time to the most recent common ancestor (TMRCA) for two males depending on how closely their individual haplotypes match each other.
Y-DNA testing currently available includes both SNP and STR testing. For STRs, a male may order anywhere from 12 markers to over 100 markers. The industry standard is generally 37 or 67 markers at this time. Individual SNPs or panels of SNPs can be ordered to determine and refine one's haplogroup. Scientists and hobbyists are continually discovering new SNPs, this further refining the Y Haplogroups.
For further clarification on the Y Chromosome (for beginners) go to Sorenson's Animations here.

mtDNA Testing

mtDNA stands for Mitochondrial DNA and is easily remembered as "maternal line DNA." In contrast to autosomal and Y-DNA, Mitochondrial DNA is located outside the cell nucleus. This type of DNA is inherited through the direct maternal line and can be passed down virtually unchanged for thousands of years. Because of this, mtDNA can reveal much about one's maternal line ancient origins. It is passed from mother to daughter, so a woman's mtDNA will be the same as her mother's mother's mother's mother and so on. Males do inherit this DNA from their mothers, but they do not pass it on to their children.

Upon receiving your mtDNA results, you will be assigned a haplogroup based on the mutations that differ from an early sample of European mtDNA known as the Cambridge Reference Sequence (CRS). This assignment groups you with those who share the most similar mtDNA with you, although it may not be exact. For genealogical purposes, an exact match is, by far, the most useful.

There are currently three levels of testing: HRV1, HRV1 & HRV2 and the Full Mitochondrial Sequence (FMS). The FMS is the most comprehensive and highest resolution mtDNA test. It examines all 16,569 locations of the mitochondrial DNA.

For further clarification,  please watch Sorenson's animation on mtDNA.

Further reading: The differences between X Chromosome Testing and mtDNA Testing

Your Genetic Genealogist

I began researching my family's history in earnest in 2002. Since then I have made amazing discoveries about my ancestors and myself. Up until recently, most of my work has been centered around old records and faded photos. In the last couple of years, I have been fascinated by the subject of DNA testing for ancestry purposes. Recently, I was fortunate to have participated as a Beta Tester for both 23andme's Relative Finder and FTDNA's Family Finder- the groundbreaking new autosomal DNA testing products. In this capacity, I have spent countless hours learning all that I could about this amazing new science - both its potential and its limitations. After answering the same questions for my family, friends and other genetic genealogy researchers repeatedly, I have decided to start blogging in order to have a central location for all of the exciting new discoveries that are being made in my family tree and in our genes, as well as to answer all pertinent questions from interested parties. I have convinced upwards of 15 family members to take this new test and will use this site for comparing and contrasting their results as well. Please keep in mind that this is an emerging science and we are all learning it together.
I have chosen the name "Your Genetic Genealogist" because I hope to assist all of you in discovering your genetic roots on this journey to discover mine.