How much of the genome is shared among the family members? Part 1

In this chapter we are going to talk on the genome and the family. So, my genome in relation to the genome of the people surrounding, and we are going to see how much of this genome is shared among the family members, what is the inbreeding and why it has been so interesting in many populations to be really forbidden, and we are going to talk also how this idea of sharing genome, is important for what is called the sociobiology thought. Finally, we are going to have some views on the uniparental genomes, meaning the mitochondrial DNA and Y chromosome.

We know, very well, that we share our genome with our parents, of course, the mother and the father, they both give us one half of the autosomes. The father may, to the males, give the Y chromosome, and always the mother will give the mitochondrial DNA. But now we are going to concentrate on the autosomes. This means that we share one half with each of them, with our sibs (or siblings), brothers and sisters, we share also one half.

But in this case, it is one half statistically, meaning that is not deterministic as one half of the father one half of the mother, but in this case you can calculate the probabilities of having the same information of your sib, ¼ for the one coming from the mother, ¼ for the one coming from the father, and, at the very end, is ½. In some cases, by random events it’s a little more or is a little less, but in all cases is ½. You can do this calculation of this sharing of 1/2 with your sibs, and going to other family members. So here you have all the amount of sharing of the autosomal genome with all family members.

1/2 with your brothers and sisters, 1/4 with your uncle’s, 1/8 with the first cousin. This is the one we are going to point because this is the most interesting one, because it’s far enough to be allow to marry, but still the amount of sharing is quite high. You can see that, if you go further away, it decreases very, very, very rapidly.

In the 23andme analysis of my genome, these people detected that I had a cousin in the database and they said: “Look at that Jaume, you have a 4th cousin in the database”. In this case, they could do that because they saw that we share fractions of our genome, and we can calculate this amount of sharing, and the amount of sharing is related to the relationship we have between the two people. And in this complex table, you can see how we can go from the amount of sharing of the genome between two individuals and which is the family relationship they have.

So in this case is interesting, because you can recognize even distant relationships among people that didn’t know that this relationship existed. But let’s stick to the first cousin, in which the sharing is 1/8, means around 12,5%. Again, a percent that maybe a little more or a little less, and in some cases people share really a little more of this and some others a little less… meaning that not always is possible to recognize exactly the degree of family relationship among us.