Wageningen University & Research: New division in genetic load helps species conservation

A novel division in genetic load can take research in avoiding harmful mutations in the genomes of endangered species to the next level. This genetic load should be split into the masked- and the realized load. Thus write researchers from, among others, Wageningen University & Research in an article published Nature Reviews Genetics.

Suppose you want to protect a small, endangered population that is threatened by inbreeding. ‘The approach to date has been to introduce fresh blood into the population’, says Mirte Bosse, a researcher involved in endeavours such as protecting the Asian elephant. ‘This is generally successful in the very next generation because these offspring have genes from both the old and new gene pool. However, after two or three generations, you see an increased number of hidden issues because the combination of genes in that generation may be an unfortunate one.’ These problems could be prevented through better insight into the genetic load.

Lower fitness
Evolution causes a considerable genetic variation, part of which may ultimately cause a drop in a population’s fitness level. A less fit population of red pandas for example is more prone to disease, weaker and less fertile.

This reduced level of fitness is caused by mutations that have an adverse effect on, for example, how a gene functions. These adverse effects often only become visible if the mutation is passed on to the offspring by one of the parents. If only one defective gene is present, but there is also a still functioning gene, the adverse effects are masked.

Future populations
Modern research methods such as genome sequencing and other computer-driven methods have increased our knowledge of genetic load. Scientists are increasingly adept at measuring mutations that may cause genetic load and are increasingly able to predict what mutations may cause issues in existing or future populations. For example, mutations seen in parts of the dna sequence that is highly conserved across the tree of life, are more likely to have a damaging effect because this sequence has proven its value over millions of years of evolution. These techniques have been developed for the genetic analysis of humans and model species, but now also used in threatened species by building on this knowledge.

By combining modern methods with existing research, a group of scientists has succeeded in predicting what the genetic load means for the potential fitness of future populations. The scientists aim to split the genetic load into two distinct types: The realised load, which lowers the existing population’s fitness, and the masked load, which reduces the fitness of future populations through adverse genetic mutations.

This loss of fitness can become a problem when the population shrinks over time, resulting in increased inbreeding. Thus, the realised load accumulates.

Modern genetic research methods and this new division could provide a useful supplement to current research on protecting and conserving endangered species. ‘To see how much genetic variation is still present within a species’, Bosse explains. ‘The current focus in biodiversity is primarily on speciesabundance and richness, but genetic diversity and quality within a species is also important.’

In this type of research, having a uniform measuring standard to determine the genetic load from genome sequences is very important. The international collaboration between researchers from the Netherlands, England, Italy and Denmark is an excellent step towards this goal.

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