The Y chromosome is passed down from father to son in an unbroken line all the way back to our earliest ancestors in Africa. Only genetic males carry the Y chromosome. Sometimes a small change in this genetic code, called a mutation, occurs from one generation to the next. These mutations often do not affect the proper function of the body, but when they occur, they tend to get passed down to the next generation of males.
When two paternal lineages diverge from a common ancestor (e.g., two brothers and their individual descendants), the two lineages will start to accumulate unique mutations over time. For this reason, studying the mutations in different lineages is particularly useful for determining how they differ from one another and when they split apart.
There are two main types of Y-DNA testing for genealogists: Y-SNPs and Y-STRs.
When a mutation occurs in a single location on the chromosome, it is called a Single Nucleotide Polymorphism or a SNP (pronounced snip). SNPs do not happen frequently, and many generations may occur without change. When a SNP occurs, it does not usually mutate back to the ancestral form.
They can occur independently in different lineages over time but are often unique to a single lineage. Studying a large set of SNPs can help identify how each lineage connects to the tree of all humankind from the distant past all the way down to the present day in some cases.
For more information about Y-SNP testing, click here.
There are some areas where a DNA sequence is repeated many times. We call these areas Short Tandem Repeats (STRs). The number of times the sequence repeats in an STR is called the value of the STR, and the number of repeats can change from one generation to the next. While they do not occur every generation, they tend to change more frequently than SNPs because they cover a larger region of the chromosome. STR values can be shared among many lineages, so they are most useful when studied in sets. This helps to see general patterns of change. The larger the set of STRs that are compared, the more accurately we can predict how close in time their common ancestor lived.
For more information about Y-STR testing, click here.
How SNPs and STRs are Useful
Both SNPs and STRs can be useful for tracing paternal lineages to a common male ancestor. This is done primarily through making connections to living male relatives who share similar mutations passed down from that ancestor. Studying the degree of change between test takers and comparing their family histories can help pinpoint that ancestor. Their geographic dispersal can help shed light on ancient migration patterns as well.
The two types of mutations (STRs and SNPs) provide information about your paternal heritage, but they do so in slightly different ways. For this reason, FamilyTreeDNA offers different levels of Y-DNA testing.
FamilyTreeDNA Y-DNA Tests
The Y-37 test analyzes a set of 37 STR markers and compares it to other sets in the database. Generally speaking, the more STRs two people share in common, the closer in time they share a common paternal ancestor. This allows people to collaborate on their genealogy to find this shared ancestry. The Y-37 test is a good introduction test to find matches, though some of these matches might be quite distantly related to you.
There are many more than 37 STR markers that can be compared between two individuals. The more STR markers you compare, the more accurately you can determine the closeness of relationships. The Y-111 test is the highest level test to compare Y-STR markers and significantly refines your matches to determine the closest matches to you.
The Big Y-700 test includes both STR and SNP results and provides matches for both. In addition to the STR markers included in the Y-111, it provides a minimum of 589 additional markers, giving you a total of 700 STRs, though only the first 111 are used for matching. These additional markers can be useful for determining mutations unique to a lineage, clan, or patriarch.
In addition to STRs, this test provides hundreds or even thousands of SNP results. This helps pinpoint you in the ever-growing tree encompassing all of humanity. Some SNPs occurred thousands of years ago and are shared by almost all of humankind, while some SNPs are very recent, arising even within a living person. For this reason, SNPs provide both deep ancestry and modern connections. They trace the migration journey your ancient paternal ancestors took out of Africa all the way to the modern day.
SNP Packs test a preset number of SNPs tailored to your specific haplogroup and are designed to help refine the haplogroup prediction you receive with a Y-STR test such as the Y-37. Unlike the Big Y-700, it is not exploratory and is not updated over time. However, SNP Pack tests do guarantee results for all SNPs included in the pack.