Y Chromosome

The Y Chromosome

The Y Chromosome is one of two allosomes - sex-defining chromosomes. The two allosomes form one of the twenty-three chromosome pairs in every cell in the human body. Typically, women have two X chromosomes - one from their mother and one from their father. Men, however, have an X chromosome - inherited from their mother - and a Y chromosome - which always comes from their father.

The Y Chromosome spans around fifty-nine million base-pairs and represents almost 2% of the total DNA in a human cell. It is estimated that the Y Chromosome contains around fifty to sixty genes that provide information for making proteins. As only males carry the Y Chromosome, these genes tend to be concerned with male sex determination and development.

People sharing a Y Chromosome subtype share a similar amount of DNA as they would with their third or fourth cousin.

Why the Y?

The Y Chromosome is the single largest piece of DNA inherited as a block, and always coming from the father, it is a very useful tool in uncovering male ancestors. It remains largely unchanged as it passes from father to son, as it does not have a matching chromosome to recombine with.

The Y Chromosome is very interesting, because such a big block is inherited together, there is about one new genetic variant per generation or two. This means that complete Y Chromosome sequences should, in theory, allow us to reconstruct a family tree of all men on earth, accurate to a couple of generations. In reality, it is not simple to read all the letters of the Y chromosome; however a very refined tree can be built. As we improve resolution, the potential for improved interpretation increases too.

Your Y Chromosome

If you are a male, your Y Chromosome came from your father, which in turn came from his father, and so on, and so forth. You will share this Y Chromosome with any paternal blood uncles and will pass it onto your male children.

For a female to trace her fatherline, the best approach is to test a brother - as he shares both the motherline and fatherline. The next best volunteer would be your father himself, or paternal uncle, but this would give their motherline - your paternal grandmother’s mitochondrial DNA.