he Four Horsemen Of Genomicalypse: Fuzzy notions in genomic selection I describe four notions that I found ill-defined in genomic selection. Linkage Disequilibrium plays a vital role in genomic selection, yet we lack of conceptual tools to measure, describe, and predict multilocus linkage equilibrium. There is no consensus on what “relationship” means – we suggest to base it on observed similarity at markers. Effective number of markers should ideally be a populational parameter with a clear estimation method and interpretation. We should not conclude from simulations with oversimplified genetic architecture which assumes additive genetic architecture and point locations of QTL loci