Scientists from The University of California at San Francisco (USA) announced a discovery that could be crucial in explaining the female longevity.
Throughout the world, women live longer than men, a trend that is not unique to humans, as it is also found in most animal species.
Now, researchers say that the cause of this phenomenon could be the important role played by the second X chromosome present in female mammals. This chromosome contains many genes related to the brain and is essential for survival: without at least one X, an animal can not live.
For its part, the Y chromosome, present only in males, is not necessary for survival and contains very few genes apart from those that create secondary sexual characteristics, such as male genitalia and facial hair.
In their experiment, the team modified the chromosomal combinations in mice. Apart from the combinations that are found in nature – women with XX chromosomes with ovaries and males with XY with testicles – created two laboratory combinations: males with XX chromosomes with testicles and females with XY chromosomes with ovaries.
The mice were genetically identical, except for their sex chromosomes, and they grew in the same environment. Likewise, those who had two X chromosomes lived longer than those who had one X chromosome and one Y chromosome.
The mice that had a combination of XX chromosomes and ovaries were the ones that lived the most. On the other hand, the XX combination in the males with testicles protected the animals from premature death, but without prolonging their life beyond the normal expectation.
“Those who had the XX combination escaped premature death”
“For a longer lifespan, the mice needed to have ovaries and XX chromosomes,” said Iryna Lobach, one of the co-authors of the study. “But in terms of living a normal life, it did not matter if they had ovaries or testicles. Those who had the combination XX escaped premature death during aging,” the researcher stressed.
Carrying out the study required several years because the mice were observed for 30 months, during which period they died or survived. The benefits of having two X chromosomes began to be evident when the animals were 23 months or older.
