Evolutionary aging models: reproductive regimes and the Y chromosome degeneration. / Modelos evolucionários de envelhecimento: regimes reprodutivos e a degeneração do cromossomo Y.

AUTOR(ES)

Matheus Pereira Lôbo

DATA DE PUBLICAÇÃO

2003

RESUMO

Aging theories can be classified in two types: biochemical theory and evolutionary theory. The biochemical theories explain ageing due to imperfections on the biochemical process responsible for the maintenance of life. The evolutionary theories explain aging without any biochemical mechanisms. They support only adaptive strategies, such as reproduction, heredity, mutations and natural selection. In this work we studied theoretical aging models in the light of evolutionary theories. A successful ageing model was proposed by Penna in 1995. This model can reproduce a large amount of biological features. We present a review with its most important results, including catastrophic senescence and Gompertz law. We also present the sexual version of Penna model and some consequences of sexual fidelity and sexual selection. An alternative aging model was proposed in 1995, known as Heumann- Hotzel model. At the beginning, this model did not succeed due to some unrealistic features. A few modifications were necessary to give the model interesting properties. We studied, through numerical simulations, alternative forms of reproduction in the modified Heumann-Hotzel model, including sexual reproduction with and without crossing-over, meiotic parthenogenesis, apomictic parthenogenesis, hermaphroditism and parasex. We also investigated and compared what is the best strategy: haploid or diploid populations, asexual or sexual reproduction and, in this case, with or without crossing-over. One version of the sexual reproduction deserved special attention. We propose a sexual version of the modified Heumann-Hotzel model, in which the populations genomes have the same symmetry as the sexual chromosomes. This model was denominated Y Chromosome Model. In comparison to the other chromosomes, the Y is poor in genes and it is often called a genetic junkyard. It has fewer genes than X chromosome and one third of its length. Besides, the Y chromosome has a large amount of repetitive gene sequences and only a small number of them have some sort of function. In men, the X and Y-chromosomes do not recombine with each other, while in women their X chromosomes do recombine with each other. Today we know that the Y chromosome degeneration occurs due to its lack of recombination. In this work we show an alternative explanation for the Y chromosome degeneration. Even in the absence of recombination and when the same number and intensity of mutations are applied on the X and Y-chromosomes, more mutations are accumulated in the Y chromosome. We conclude that natural selection leads to Y chromosome degeneration.

ASSUNTO(S)

natural selection regimes reprodutivos seleção natural aging model modelos de envelhecimento reproductive regimes mutation y chromosome degeneration física biológica mutação biological physics degeneração do cromossomo y

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