THE GENETICS OF THE PORTUGUESE PEOPLE I

In the last 20 years genetic tests have become more comprehensive, faster and cheaper. The evolution has been such that, nowadays, it's at the reach of anyone (and of most pockets) to do a genetic test, sequencing a large part of his or her genome. The genetic databases have grown in an astonishing way. This allows that, today, you can make a genetic characterization of many human populations, in particular European ones – that have been under more intense study.

It is now possible to make a generic description of the genetics of the Portuguese people, its origins e how it compares with other populations. It's that description that I will make here. But right from the start I want to make it clear that the notion of Portuguese people that I will use considers only Portuguese persons that are 100% Portuguese in 3 or 4 generations (all grandparents or great-grandparents are Portuguese) and only those that are Caucasoid (white). These criteria may be criticized, but I will use them because they are also used in most scientific studies.

To understand my description of the Portuguese genetics you need to know first some simple notions and their consequences, that I will now explain shortly.

Lets divide a persons DNA in 3 different kinds: autosomal DNA, which is the DNA that determines our biological characteristics (such as our physical traits); the sexual DNA, comprised by the X and Y chromosomes and mitochondrial DNA, which regulates the production of energy inside the cells. I make this sorting because each of these kinds of DNA give us a different type of information about our genetics and its origins. Autosomal DNA is the one that we really want to know, because it's the one that has the information that determine the the way our body works and the way it looks (phenotype). The problem is that it is difficult to extract information from this kind of DNA with the objective to describe a population or to find its origin. This is because, on one side, it goes through recombination – lets say it is shuffled and reorganized when the person is conceived – and, on the other side, if it is easy to find genetics differences between to persons, it is a lot more difficult to identify differences between groups or population. When it comes to mitochondrial DNA and the DNA of the Y chromosome, things are much more simple.

Our mitochondrial DNA is inherited exclusively from the maternal side. It is, except in the case of some mutation, exactly identical to our mother's. This gives us a female line that we can trace back thousands of years.

Chromosome Y's DNA is inherited exclusively from the paternal side, being identical from father to son. Just as with mitochondrial DNA, with YDNA it's possible to trace back a person's paternal line thousands of years.

The mitochondrial and YDNA lineages are divided in Haplogroups (Hg). Each haplogroup is identified by a letter (v.g. R) and when a mutation occurs inside the haplogroup, a number is added to the letter (v.g. R1, R2, and so forth). When another mutation happens inside one of these subgroups, another letter is added (R1a, R1b, etc). Since it's possible to date these mutation, we can know how we stand in each group and subgroup though time.

So, I will start by presenting the male lineages (Hg YDNA) that exist in Portugal. Check the next post. (This blog in portuguese: http://geneticaportuguesa.blogspot.pt).