22 July 2016

Why do women live longer than men

The hypothesis of a protected X chromosome has been confirmed

Sergey Syrov, XXII CENTURY, based on the materials of R&I World: XX protection against age-related mutations

Women in developed countries live on average 3-8 years longer than men, even after adjusting for higher mortality in infant boys. The same difference in life expectancy is characteristic of other mammals and some insects. There are several hypotheses explaining this phenomenon, and one of them is the "protected X-chromosome hypothesis".

Specialists of the Institute of Biodiversity and Evolutionary Biology named after Antonio Cavanilles at the University of Valencia (Spanish L'instituto Cavanilles de Biodiversidad y Biología Evolutiva per la Universitat de València) and the University of Oxford tested the "hypothesis of the protected X chromosome" in a study on fruit flies and confirmed that the cause of the difference in life expectancy of males and females may indeed be a protective effect the second X chromosome.

The researchers analyzed the life expectancy of male and female fruit flies – fruit flies in lines with different levels of inbreeding. The work, published in the journal Biology Letters, adds empirical evidence to the "protected X chromosome hypothesis" proposed 30 years ago to explain why males carrying XY sex chromosomes age faster than females with XX chromosomes. In particular, the study confirms one of the main predictions of the hypothesis: inbreeding shortens the lifespan of females more than males.

Pau Carazo, head of the research group at the University of Valencia, explains:

"The difference in life expectancy between males and females can be explained in part by the fact that the accumulation of mutations during life, or their transmission from generation to generation, has a greater impact on the sex, which has only one, "unprotected" copy of the X chromosome; as a rule, these are males.

If the protection effect exists, we can assume that inbreeding affects the lifespan of a homogamous sex (the one whose sex is determined by two identical sex chromosomes) to a greater extent than a heterogamous sex (with two different sex chromosomes). This is because the last group of the X chromosome is always "unattended", with or without inbreeding, while the first group of the X chromosome is "protected" only if two X chromosomes are different, which does not happen after multiple inbreeding."

The experimental results are consistent with this prediction.

The explanation for the protective effect is that most genetic mutations are recessive in nature. For those with two X chromosomes, this means that they experience a negative mutation effect only when the same mutation occurs in both copies of the X chromosome, otherwise they simply do not manifest. In the case of XY, any mutation present in the X- or Y-chromosome can manifest itself in full. So, having obtained two identical X chromosomes in female fruit flies by inbreeding, the researchers essentially nullified the protective effect of the second X chromosome, Recessive mutations manifested equally among males and females.

The difference in the life expectancy of males and females is explained by other hypotheses.

The dependence of life expectancy on sex may reflect differences that have appeared during natural selection. The increased risk of death from external causes may be explained by behavioral features that are associated with sexual selection.

The cause may also be the asymmetric inheritance of cytoplasmic genomes (the hypothesis of the "maternal curse").

Portal "Eternal youth" http://vechnayamolodost.ru  22.07.2016

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