What are the differences between SNPs and STRs?
An STR is a short tandem repeat. This is a place in your DNA code where a letter sequence is repeated. For example, AGTAAGTAAGTA is three repeats of the sequence AGTA. STRs have a fast mutation rate. When they change, it is an increase or decrease in the number of repeats. STR values changing back (back mutate) are more common.
A SNP (pronounced snip) is a single nucleotide polymorphism. That means that it is a single small change in your DNA code. These changes are rare. Once they happen, they seldom change back (back mutate). A back mutation is when a marker value changes back to its original value.
What do the numbers on the Y-DNA - Standard Y-STR Values page mean?
The number below each STR marker indicates the number of times a particular sequence of alleles repeats itself in a specific location on the Y chromosome. The value of testing Y-DNA STR markers comes from creating a Y-DNA signature (haplotype) with them and comparing that Y-DNA signature to others in a database. They are useful for genetic genealogy because your Y-DNA signature distinguishes your paternal lineage from others. They can then be used with FamilyTreeDNA’s comparative database to discover genealogical connections or historic ancestry.
What do the DYS, DYZ, DYF, and FTY prefixes on Y-DNA STR names mean?
The DYS, DYZ, and DYF prefixes are part of the scientific name for a short tandem repeat (STR) found on the Y chromosome. STR markers are named according to guidelines published by the HUGO Gene nomenclature committee (HUGO). For Y-DNA STR tests:
- D stands for DNA.
- Y stands for Y chromosome.
- S, Z, and F stand for the complexity of the repeat segment as follows:
- S is a unique segment.
- Z is a number of repetitive segments at one site.
- F is a segment that has multiple copies on the Y chromosome.
The FTY prefix stands for Family Tree Y. For now, this prefix acts as a placeholder until HUGO assigns an official prefix to these STRs.
All STRs are given a unique identification number.
For example, DYS393: the D indicates that the segment is a DNA segment, the Y indicates that the segment is on the Y chromosome, the S indicates that it is a unique segment, and the number 393 is the identifier.
Why do I have more than one result for an STR value?
Some STRs are considered multi-copy markers because there are copies of the STR in multiple locations on the Y chromosome. Each location of the marker changes independent of the others, so it is common to have different values for each copy.
For example, DYS385 usually has two copies.
Why do some of my Big Y-700 Panel 6 and 7 allele values differ from results I've received from other companies?
At FamilyTreeDNA, we typically count only perfect repeats; therefore, some of the Big Y (Panels 6 and 7) Y-STR allele values will consistently differ from that of other companies. The difference will be offset by only a few values above or below the results you’ve received elsewhere.
I transferred my Y-STRs to FamilyTreeDNA, why did some of my marker values change?
FamilyTreeDNA and Sorenson Labs use different standards to report four STR (short tandem repeat) marker values. After you transfer your results, we convert them to FamilyTreeDNA’s standard. The four markers that will change are DYS441, DYS442, Y-GATA-A10, and Y-GATA-H4. Some of the Big Y-700 (Panels 6 and 7) Y-STR allele values will consistently differ from that of other companies
Should I upgrade to additional Y-DNA STR markers?
You should test more Y-DNA STR markers when you want to compare additional markers against others with similar results.
Additional STR markers will refine your matches. If you currently have many Y-12, Y-25, Y-37, or Y-67 matches, you should certainly consider upgrading your Y-DNA profile to a higher level.
The level that you choose and the need to upgrade depends on:
- Your goals,
- The amount of testing already completed by others in a Group Project that you are joining,
- The degree of certainty for a relationship (match) that you desire.
For genealogical matching, the most important factor is the degree of certainty that your near or exact matches are indeed related to you in recent generations. FamilyTreeDNA offers several levels of testing for our Y-DNA tests.
Generally, testing additional STR markers will:
- Narrow the expected time to a common ancestor with an exact match,
- Increase the degree of certainty for a near or exact match,
- Reduce the number of irrelevant matches.
You may always upgrade to a higher level of testing as your number of matches and needs change.
Please note that only panels 1 through 5 are used for matching purposes in our database.
Do more Y-DNA STR markers improve the quality of matches’ information?
You should test more Y-chromosome DNA short tandem repeat (STR) markers when you wish to compare additional markers against others with similar results. They will refine your matches for genealogical purposes. It does not increase the number of generations traced by a Y-DNA STR test but rather reduces the range of generations in the time to a common ancestor with your match.
Testing additional STR markers can also help refine the matches on the Y-DNA Ancestral Origins page. Testing more markers means that the information is more relevant to your personal ancestry. However, information on deeper origins (historical and anthropological) may be better answered with an extended Y-DNA SNP test such as the Big Y-700.
If you do not have many matches or do not have many matches that have tested more markers, you may still choose to upgrade. That way as the database grows and you gain additional matches, you will be prepared to make comparisons that are more refined. Note that our Y-111 is new enough that matching and information from matching may be limited by our current database size. This test is becoming more popular and the database is growing rapidly, so this should change over time.
Why do some of my Big Y allele values differ from results I've received from other companies?
At FamilyTreeDNA, we typically count only perfect repeats; therefore, some of the Big Y-700 Y-STR allele values will consistently differ from that of other companies. The difference will be offset by only a few values above or below the results you’ve received elsewhere.