Universiteit Leiden

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Research project

Evolutionary traps – Balanced lethal systems

How do balanced lethal systems originate and persist in nature?

Ben Wielstra
ERC Starting Grant ERC Starting Grant
NWO promotiebeurs voor leraren NWO promotiebeurs voor leraren
  • Naturalis Biodiversity Center 
  • University of California, Los Angeles, USA 
  • University of Sheffield, UK 
  • University of Belgrade, Serbia
  • Jagiellonian University, Kraków, Poland 
  • University of Kentucky, Lexington, USA

In a research program funded with an ERC Starting Grant and an NWO promotiebeurs voor leraren, Ben Wielstra and his team explore the role of genome rearrangements in the evolution of balanced lethal systems. In a balanced lethal system, two chromosome forms carry distinct lethal alleles that are reciprocally compensated for by functional genes on the alternate form. In effect, both are required for survival. Yet, parents randomly pass these forms on to the next generation. Under Mendelian inheritance, exactly 50% of the offspring receive two copies of the same chromosome form and are therefore not viable. Balanced lethal systems appear to defy evolutionary theory: such incredibly high mortality should quickly be eliminated by natural selection. Wielstra leads a genomic study of the best-known case of a balanced lethal system (chromosome 1 syndrome in Triturus newts), combined with theoretical modelling, to understand balanced lethal system evolution.



  • Wielstra, B. (2020). Balanced lethal systems. Current Biology 30(13): R742-R743.
  • Meilink, W.R.M., France, J., de Visser, M.C., Wielstra, B. (2021). Balanced lethal systems: an evolutionary mystery. Frontiers for Young Minds 9: 632945.
  • Berdan, E.L., Blanckaert, A., Butlin, R.K., Flatt, T., Slotte, T., Wielstra, B. (2022). Mutation accumulation opposes polymorphism: supergenes and the curious case of balanced lethals. Philosophical Transactions of the Royal Society B 377(1856): 20210199.
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