Y-DNA refers to the DNA found on one of the sex chromosomes, the Y-chromosome. (The other sex chromosome is the X chromosome.)

Sex chromosomes usually come in pairs and play a role in development, especially of primary and secondary sex characteristics. Having one Y and one X chromosome is most often associated with male, whereas having two X chromosomes is most often associated with female. There are also intersex people who are born with sex chromosome combinations other than XY and XX.

Most everyone gets one X chromosome from their biological mother. Your biological father usually contributes either a Y chromosome or an X chromosome.

What Are Y-DNA Haplogroups?

A haplogroup is really just a stretch of DNA commonly found in certain populations. A Y-DNA haplogroup, then, is a stretch of the Y chromosome that you share with other members of your paternal line who carry a Y chromosome.

It turns out that because the Y chromosome, unlike the other human chromosomes, does not have a nearly identical partner, Y-DNA can be traced far back into the past.

Y-DNA haplogroups are usually determined by looking at single nucleotide polymorphisms (SNPs). A SNP (pronounced “snip”) is a variation of one DNA building block, or nucleotide, at a single position in the DNA sequence. For example, at a single position on the Y chromosome most people have the nucleotide thymine (T) but a few people have an adenine (A) instead.

Haplogroups can also be determined by looking at short tandem repeats (STRs). An STR is a short sequence of DNA that repeats itself, such as GAT repeating (GATGATGAT). Both SNPs and STRs help group together people who have the same differences.

What Is Y-DNA Testing?

Y-DNA testing is a way to trace your ancestry back into the distant past. You can see back thousands and even tens of thousands of years ago. But the trick is that it only traces back the paternal line. This means that you will miss out on any family history discoveries related to your maternal lineage. It is also not possible to take this test yourself if you do not carry a Y chromosome.

What Are the Main Alternatives to Testing Y Chromosome DNA?

The three main types of DNA tests are:

• Y-DNA
• Mitochondrial DNA (mtDNA)
• Autosomal

A Y-DNA test, as mentioned, only looks at the paternal line. A mitochondrial DNA (mtDNA) test only looks at the maternal line of ancestry. It examines mtDNA, which is passed to offspring through the biological mother’s egg.

An autosomal test looks at the DNA of your autosomes. Autosomes are the 22 numbered chromosome pairs in your cells, that together with the pair of sex chromosomes make up the 23 pairs of chromosomes typically found in humans.

You inherit autosomal DNA from both of your biological parents. This type of test is best for helping you find recent relatives on both sides of your family tree.