Theories on the genetic advantages of sexual reproduction abound within the biological sciences community, but there has been scant evidence at the molecular level to reinforce such hypotheses. However, researchers at the University of Montreal and the Sainte-Justine University Hospital Research Centre in Montreal, Canada believe they have found genomic evidence that reveals human’s susceptibility to disease gradually decreases as our genetic material continues to blend together.
The production of offspring from one generation to the next pushes human evolution forward ever so slightly through genetic recombination events between parental chromosomes. For many years scientists have been aware that these recombination events do not occur in a uniform fashion. Some areas of the genome have a high-frequency of recombination while others very low or not at all.
Interestingly, the Canadian researchers found that the regions of the human genome with low recombination frequency had a higher proportion of disease-causing mutations. Moreover, the accumulation of mutations within these regions increases until a recombination event occurs. This led the team to the conclusion that our genetic code deteriorates before it begins to improve by shuffling of genes through sexual reproduction.
“Since these mutations rest on less dynamic segments of our genome, the process can potentially take many hundreds of generations,” explains Philip Awadalla, Ph.D., associate professor of population and statistical genomics at the University of Montreal, director of the CARTaGENE project and senior author on the study.
The results from this study were published online recently in Nature Genetics through an article entitled “Recombination affects accumulation of damaging and disease-associated mutations in human populations”.
Dr. Awadalla and his team analyzed the sequences from hundreds of genomes contained in the CARTaGENE genetic data repository, as well as the multinational 1000 Genomes Project database. They observed that the low-frequency recombination regions, known as “coldspots”, accrued a significantly higher proportion of damaging mutations than high-frequency recombination sites.
“This discovery gives us a better understanding of how we, as humans, become more or less at risk of developing or contracting diseases,” says Dr. Awadalla.
Additionally, the investigators were able to compare this phenomenon across population backgrounds from four distinct, present day regions: Africans, Asians, Europeans, and Canadians of French descent. While all the groups exhibited the “coldspot” mutation frequency events, there were varying degrees for the occurrences among the populations. For example, genomes from African individuals were observed to have the smallest relative proportion of disease-associated mutations and Western Europeans the highest.
“The influence of recombination rate on variable mutation accumulation across the genome clearly has an impact on disease mapping strategies. Therefore, a deeper understanding of how the processes of recombination, selection, and mutation work together to shape the landscape of deleterious diversity will improve one's ability to interrogate individual genomes for disease-causing mutations in humans,” concluded the scientists.