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. 2023 Jan 18;42(8):e112600. doi: 10.15252/embj.2022112600

Figure 2. Ancient paralogous centromere pairs explain aneuploid frequency.

Figure 2

  1. Aneuploid frequency in histone‐humanized yeasts. Chromosomes displayed are divided into two groupings based on paralogs (i.e., Chr I is the paralog of Chr VII). The average frequency of aneuploidy in histone humanized yeast for each chromosome is shown at the bottom of the green‐colored heat map. Each row represents the chromosomal copy number for a single humanized lineage either from this study and Truong and Boeke (2017).
  2. Difference in aneuploid frequency between paralog pairs, colored circles next to chromosomes indicate the average aneuploid frequency in histone humanized yeast as defined in panel (A). Paired t‐test between the mean aneuploid frequency of paralog group A and B P = 0.004. Ancestral CENs and paralog pairs are taken from Gordon et al, 2011.
  3. Number of observed aneuploidies for each chromosome as a function of chromosome size. The Pearson correlation coefficient (R) is shown for the three models (only group A chromosomes, green; only group B chromosomes, beige; all chromosomes, black). The data are best explained by two models that consider chromosomes from group A and B separately, extra sum‐of‐squares F test P = 0.0203.
  4. Model of paralogous chromosome/centromere evolution. An initial speciation event (1) led to the creation of paralogous centromeres. Following speciation, each lineage accumulated specific modifications of its chromosomes and centromeres (indicated by the accumulation of colored bars on the ancestral gray bar). After millions of years of evolution (Marcet‐Houben & Gabaldón, 2015) these two lineages hybridized, producing the ancestor of S. cerevisiae (2). This new species would have 16 centromeres, with 8 arising from each parental lineage, each carrying with them the lineage‐specific modifications. We hypothesize that given the bias in aneuploid frequency between these paralog pairs in modern S. cerevisiae, the ancient origins of centromeres in S. cerevisiae may still retain functional consequences today.