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Presence of MUC7 gene and PTS tandem repeats in mammals.
(a) Heatmap of pairwise nucleotide differences between each repeat sequence within and among primate MUC7 PTS-repeats. Different colors on the right and bottom axes indicate different species. The number shows the position of those repeats in their MUC7 repetitive regions (e.g., Rh_1 indicates the first repeat from the 5′ in the rhesus macaque reference genome). The colors in the heatmap show the nucleotide differences between each pair of repeats, with warmer colors indicating a higher number of nucleotide differences. The groupings (clusters) shown on top and to the left of the heatmap were constructed based on sequence similarity without any a priori hypothesis. Note that, if there is no recurrence and most repeats share a common ancestor, then we expect to see clustering of orthologous repeats. Instead, we observed clustering of repeats within species, indicating species-specific duplication events; (b) Number of total T and S amino acids in each MUC7 protein in relation to the number of TS tandem repeats in primates and other mammals. Relevant species and apparent outliers were indicated by a red circle and their names on the graph. If a species did not show any subexonic repeat content, it is designated by 1 on the x-axis; (c) For each repeat in primate species, the number of pairwise amino acid changes is strongly correlated with pairwise nucleotide changes both across species and within species (R2 = 0.8643), while (d) the number of pairwise TS amino acid changes are not (R2 = 0.03266). The numbers of pairwise TS amino acid remain similar within and among primate species.