A recent study published in the journal Molecular Biology and Evolution has provided strong evidence as to why many organisms reproduce sexually.

There has been long-running debate on the benefits of sexual reproduction compared to asexual reproduction. Some argue that asexual reproduction is advantageous as it does not involve resource-consuming and laborious tasks part of sexual reproduction.

However, the argument that sexual reproduction has benefits from a genetic view still persists.

The authors of the paper include post-doctoral candidate Dr. Jesse Hollister and his advisors, University of Toronto professors Dr. Stephen Wright and Dr. Marc Johnson. The three looked at various species of the evening primrose, known as Oenothera, to study the effects of sexual reproduction.

Johnson studies the evolutionary consequences of the loss of sex in evening primrose and looks at the effects sexual reproduction has on defense genes.

“There is lots of theoretical evidence to suggest that when you lose sex, that your ability to adapt to parasites is hindered,” he told The Varsity in a phone interview.

Despite the many years of studying theoretical evidence about why organisms have sex, Johnson says that virtually no work looking at the molecular evolution has been done.

The team studied 30 pairs of species, with one species in the pair reproducing asexually and the other sexually. They looked at genetic variation in species pairs and the amount of deleterious mutations accumulating in each mating type. This study was done with the assistance of the 1,000-plant transcriptome initiative headed at the University of Alberta and supported by BGI-Shenzhen in China.

“We’ve answered the question with a sledge-hammer,” Johnson says, “This is the first solid molecular evidence that loss of sex is associated with the accumulation of deleterious mutations across the entire genome.”

The study serves as empirical evidence to support the theoretical work done for many years previous.

The team showed that asexual species of Oenothera accumulate more deleterious mutations than sexual species. The paper concluded that sexual reproduction is beneficial from a genetic perspective because species do not accumulate harmful mutations as easily as in asexual reproduction due to the recombination of genes.

During sexual reproduction, the genes are separated and shuffled. These genes have the ability to recombine and prevent deleterious mutations from being inherited in the offspring. Conversely, in asexual reproduction, the species makes copies of its genome, passing on all its mutations to the next generation.

Johnson says that upcoming research will focus on understanding how loss of sex influences co-evolution with parasites, and says that he will continue to use evening primrose for studying the consequences of loss of sex.

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