(a) Example of a strain with fractional aneuploidy of chromosome XII, likely reflecting clonal heterogeneity. (b) Distribution of fractional and non-fractional aneuploidies per chromosome (n=8843 biologically independent samples). (c) Knockout of genes encoding ribosomal protein subunits frequently leads to gain of the chromosome carrying the paralog gene. (d) Ploidy plots of chromosome II for two different colonies of the hta1Δ, swi4Δ, and spt10Δ KO strains: hta1Δ cells (deleted in one of the two genes encoding histone H2A) accumulate a specific amplification of a genome region containing the paralog HTA2, a centromere, and two origins of replication). This is most likely transmitted as a circular genetic element formed by recombination between two adjacent transposon sequences. Only two other YKOC strains were found to carry the same genetic element and these were spt10Δ and swi4Δ, encoding factors controlling the transcription of cell-cycle regulated genes, including histones.