Provided is a method for mapping traits in organisms, in particular in plants. The method comprises a) providing a population of SDR-0 organisms, in particular plants, that each arise from one member of a population of unreduced cells resulting from second division restitution, in particular a population of unreduced spores; b) producing SDR-1 progeny populations of each of these SDR-0 organisms; c) phenotyping the SDR-1 progeny populations to identify segregating traits within each SDR-1 progeny population; d) if segregating progeny are present in a SDR-1 progeny population, genotyping the corresponding SDR-0 organism and comparing the genotype thereof with the genotype of the other SDR-0 organisms to identify heterozygous chromosomal regions associated with the occurrence of the segregating trait identified in the SDR-1 progeny population.