Abstract

The understanding of genetic variation is essential to decode traces that evolution has left in our genomes and whole-genome sequence data now allow us to interpret these signals at a resolution never possible before. Genetic variation in humans generally follows clines defined by geographical regions, and there are possibly very few fixed differences between any pair of continents or populations. Nevertheless, genetic differences among populations exist, reflecting mainly past demographic events and in certain cases they can be quite extreme. Elucidating the functional causes of these extreme patterns of population differentiation remains the major challenge. Both patterns of too much or too little differences exists in different regions of the same human genome and I will illustrate those cases. First, I will talk about ultrasensitive and transcribed ultraconserved regions where there is very little genetic differentiation as a consequence of negative selection. Secondly, I will show the case of region that present extreme differences between populations (highly differentiated sites) as adaptation to population-specific environmental pressure, or positive selection. Finally, I will talk about cases of population-specific lack of genetic variability due to consanguinity and isolation.