Evolution of Sex and Deterministic Mutation

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In studying evolution, there has been much debate over the origins and evolutionary maintenance of sex. This represents a great challenge in evolution as it appears that the vast majority of animals and plants reproduce sexually. One component compounding the mystery is the two fold cost of sex, that is, there is a cost to producing males. Where an asexual species can double its population each generation, the sexual species will remain at a constant population if both populations produce 2 offspring per generation. An added cost of sexual reproduction can be that there is a time investment in finding mates, as well at the potential for sexual selection which can lead to the selection of unfavorable traits. There have been a number of hypotheses for how sex is maintained. Some of these ideas include speed in creating novel genotypes, the red queen hypothesis and resistance to parasites, and being better at removing deleterious mutations. The answer to the problem of sex may be related to one or all of these hypotheses, and the maintenance of sex in each taxa may be accomplished by different means. One subset of models are those that deal with removal of deleterious genes. The fundamental reasoning in these models is that deleterious mutations can build up in a lineage such that it decreases an organism’s overall fitness. Sex is then thought to be more efficient at removing deleterious mutations from the genome through recombination. An asexual lineage would have to rely on a reversal mutation to remove deleterious alleles. Two models in this subset are Muller’s ratchet hypothesis, and the deterministic mutation model, that I will discuss in more detail. Muller’s ratchet hypothesis considers an asexual population to act as a ratchet. When mutations arise in the least mutated individuals in a population, further generations cannot have fewer mutations in that population, provided that back mutations don’t exist. This hypothesis is built under the assumption that...
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