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Untangling the Evolution of a Balanced Lethal System

Ben Wielstra, Marie Skłodowska-Curie Postdoctoral Fellow, will start his own lab at the Institute of Biology Leiden to untangle the evolution of balanced lethal systems. Wielstra is one of five researchers at Leiden University who has been awarded an ERC Starting Grant in the 2018 round by the European Research Council. ERC Starting Grants are awarded to early career scientists showing great promise.

Balanced lethal system

In a balanced lethal system, two forms of a chromosome occur and both are required for survival. Yet, parents randomly pass on one of the two forms to the next generation. Offspring with two copies of the same form of chromosome – 50% according to the rules of Mendelian inheritance – are not viable. This incredibly high mortality rate appears to defy evolutionary theory.

Inheritance table. Each parent has both form A and B of a particular chromosome. Because: both are required to live, because they each compensate a deadly allele (gene variant), shown with a X, on the other form. One of these forms, A or B, is randomly passed on to the offspring, which receives 1 copy of the chromosome from the father and 1 copy from the mother. The offspring can thus get four types of combinations: AA, AB, BA or BB. The chance of each of these combinations is 25%. Of these four options, two (AA and BB) are not viable, because they do not have both chromosome forms. The chance that a descendant is not viable is therefore 25% + 25% = 50%.
 

All we currently know about balanced lethal systems derives from classical studies that did not look deeper than embryos and cells. Theory and technology have considerably advanced since. Ben Wielstra and his research team will combine cutting-edge genetic techniques and evolutionary modeling to investigate how these bizarre balanced lethal systems can evolve.

Ben Wielstra studied Biology at the Institute of Biology Leiden (IBL) with several projects at Naturalis Biodiversity Center. He did his PhD at the University of Twente, with a strong link to Naturalis in Leiden. He continued to be associated with Naturalis, and collaborate with Pim Arntzen, but after a Newton International Fellowship at the University of Sheffield and a Marie Skłodowska-Curie Fellowship at the University of California, Los Angeles, he now returns to Leiden on his ERC-grant at a tenure track position at the IBL. Besides the solid link with Pim Arntzen and many others at Naturalis, Wielstra joins other IBL-staff with an evolutionary expertise and interest such as Klaas Vrieling, Mike Richardson, Maurijn van der Zee and Daniel Rozen.

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