Although genetically identical, for example, monozygotic twins may have different characteristics, as some genes can only express a copy that comes from their father or mother. Researchers Andrew Chess and Alexander Gimelbrant from Harvard University have reached this conclusion.
Previously they knew some of these cases. An example of this is the female X chromosome. Unlike men, women have two X chromosomes, which is a double information of this chromosome. However, to prevent the products that are generated in the expression of these genes from being also duplicated (due to the problems of proportional imbalance of the products of the genes), one of the chromosomes of women is inactive.
However, these cases were considered exceptional. Chess and Gimelbrante wanted to know if something similar happens in other genes. They took human cells individually and cultivated them in cultures. Millions of copies of cells were analyzed by a chip capable of differentiating the products produced by genes (messenger RNA) from those from mother and father. And they found that 9% of the genes studied expressed one of the copies, sometimes the other, and sometimes both. It seems to be somewhat random.